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# Chalcogen bonding in complexes based on electrophilic tellurium

Andres Padilla Hernandez, Victor Mamane

► To cite this version:

Andres Padilla Hernandez, Victor Mamane. Chalcogen bonding in complexes based on electrophilic tellurium. Coordination Chemistry Reviews, 2026, 551, pp.217416. 10.1016/j.ccr.2025.217416. hal-05404225

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Review

# Chalcogen bonding in complexes based on electrophilic tellurium☆

Andres Padilla Hernandez, Victor Mamane*

Laboratoire de Coordination, Ligands, Interactions et Catalyse (CLIC), UMR 7177 – Institut de Chimie, Université de Strasbourg, 4 rue Blaise Pascal, F-67000 Strasbourg, France

ARTICLE INFO

Dedicated to Professor Giuseppe Resnati, celebrating a career in chemical bonds on the occasion of his 70th birthday.

Keywords:

Chalcogen bonding

Lewis base

Molecular complex

Non-covalent interactions

$\sigma$-Hole

Tellurium

A B S T R A C T

Chalcogen bonding (ChB), defined as the non-covalent interaction between an electrophilic chalcogen atom and a Lewis base, is now recognized as a powerful tool across a wide range of chemical applications. The strength of the ChB depends on the nature of the chalcogen atom; consequently, tellurium species exhibit the strongest ChB, compared to their sulfur and selenium analogues. This review aims at providing the readers with an overview of systems involving electrophilic tellurium atoms engaged in ChBs with Lewis bases, both in the solid state and in solution. In early studies-predating the widespread adoption of the $\sigma$-hole concept-the presence of ChBs was proposed on the basis of the geometrical parameters obtained from the X-ray single crystal structures. Specifically, interatomic distances below the sum of van der Waals radii and the near-linearity of the interactions were considered key indicators of ChB formation. This review is organized in sections highlighting the ability of tellurium to participate in ChBs at different oxidation states (0, +1, +2, +4 and +6). Beyond structural analysis and characterization, the aim of this review is to underscore the different roles of ChB, ranging from the stabilization of reactive or unstable species to their involvement in catalytic processes and crystal engineering.

# 1. Introduction

Often considered as the forgotten element of the chalcogen family [1], tellurium is currently being extensively studied in the field of chalcogen bonding (ChB) with emerging applications in catalysis [2,3], crystal engineering [4,5], supramolecular chemistry [6], anion transport [7] and coordination chemistry [8]. The exceptional ChB ability of tellurium species compared to their sulfur and selenium analogues are due to a combination of several inherent properties of tellurium, which is the largest, least electronegative, and most polarizable and ionizable in the chalcogen series. Tellurium-based compounds are therefore able to non-covalently interact with anionic and neutral Lewis bases to form relatively stable complexes which are at the origin of the above-mentioned applications.

## 1.1. Generality on tellurium

Tellurium is a p-block chemical element with atomic number 52 and with electronic structure [Kr]4d$^{10}5s^{2}5p^{4}$. The tellurium atom exists as 8 known isotopes, out of which only 6 are stable [9], and can display a whole range of oxidation states from -2 to +6. Moreover, the isotope

$^{125}$Te has a relatively high abundance (7.07 %) and a nuclear spin of 1/2, which makes it NMR-compatible, a useful property for the characterization of tellurium-based compounds. This metalloid belongs to group 16 of the periodic table, along with oxygen, sulfur, selenium and polonium, of which it stands out as the heaviest non-radioactive chalcogen atom. Its name, given by the German chemist Martin Heinrich Klaproth, derives from the roman deity *Tellus*, the roman goddess of the Earth. Despite what its name may suggest, tellurium is relatively rare in Earth's crust, with an approximate abundance of only 1 ppb, a value lower than that of precious metals such as gold and platinum [10]. Interestingly, the value of this element alone would not justify the cost of its extraction, if it weren't because this metalloid is often found in compound minerals containing valuable elements like gold, silver and copper, such as in sylvanite ((Ag, Au)Te$_2$), hessite (Ag$_2$Te) and calaverite (AuTe$_2$) [11]. This is why this element was first described by its discoverer Franz Joseph Müller in 1782 as "aurum paradoxum", referring to an unknown substance found in Transylvanian gold ores, initially thought to be antimony [12].

Nowadays, the industrial production of tellurium is achieved by harvesting the anodic residue derived from the electrolytic refinement of copper, whose Te content is of around 2 % by weight [9]. Despite its

<footnote>* This article is part of a Special issue entitled: 'Chemical Bonds' published in Coordination Chemistry Reviews.</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail addresses: andres.padilla-hernandez@etu.unistra.fr (A. Padilla Hernandez), vmamane@unistra.fr (V. Mamane).</footnote>
## Sectorial uses of tellurium (2024)

<figure><img src="image_3.png" /><figcaption>Fig. 1. Uses of refined tellurium by sector of activity in 2024 [21].</figcaption></figure>

rarity, tellurium finds many different industrial applications. It is in fact used as an additive to copper alloys and steel, making them easier to machine. The addition of tellurium to lead metal increases rigidity and resistance to corrosion, and it can also be used to tint glass and ceramics. Furthermore, tellurium finds its use as a catalyst in industrially relevant chemical processes, such as the vulcanization of rubber [13] and the production of acrylonitrile by ammoxidation of propane [14]. However, the most important application of tellurium lies in the fabrication and development of CdTe thin film photovoltaic cells (60 % of the annual supply of Te, Fig. 1) [15]. Despite having lower efficiency than crystalline silicon photovoltaic cells, the CdTe-based counterparts are the lowest-cost producer of solar electricity [16]. This is because the high chemical stability of this alloy makes it easy to deposit over surfaces, thus facilitating large scale production [17]. The second most common use of tellurium (20 % of Te annual production, Fig. 1) is focused on the manufacture of high efficiency thermoelectric components based on alloys of Bi₂Te₃ with Sb₂Te₃ and Bi₂Se₃. Indeed, these composites possess the highest thermoelectric figure of merit of any material at near room temperature [18]. It is important to point out how much the plethora of applications for tellurium are somewhat contrasted with the relatively low supply of this element, turning it into a highly strategic

resource, so much as to be classified as “critical metal” in the US [19] and the EU [20].

All the above-mentioned examples involve inorganic Te derivatives, but the chemistry of organic molecules containing tellurium is just as fascinating as it is diverse [1]. Early studies of the organic chemistry of this element highlighted the high toxicity and foul smell or organotellurium molecules [22]. However, it was later discovered that, although this element is not an essential biological trace element unlike its lighter chalcogen relatives (O, S, Se), some organotellurium compounds are bioactive, displaying interesting properties such as immunomodulatory, antitumoral, antimicrobial or even antioxidant activities [23].

Besides, organotellurium derivatives have found strong interest in radical polymerization [24], oxidation reactions [25] and coordination chemistry [26]. In the latter field, compounds of tellurium in different oxidation states were described to behave as electron donors (Lewis base). Although diorganoditellurides (Te(I)) and tellurolates (Te(0)) were shown to be good ligands of Pt [27], telluroethers ligands (Te(II)) were the most frequently employed in coordination chemistry [28]. In contrast, only very limited examples reported the use of tellurium (IV) ligands in coordination with Ir [29], Pd [30] and Pt [31].

## 1.2. The ChB: Origin and properties

The ability of chalcogen atoms to engage in “secondary interactions” [32] was first demonstrated for divalent sulfur derivatives (R–S–R') in the solid state through a detailed analysis of the geometric parameters associated with sulfur–sulfur contacts [33]. In these systems, interatomic distances shorter than the sum of the van der Waals radii were observed, and the nucleophiles (Lewis bases) were found to approach along the extension of one of the covalent bonds to sulfur, resulting in quasi-linear arrangements. The more specific term “chalcogen–chalcogen interaction” was later introduced [34,35], before the term chalcogen bond (ChB) was adopted [36,37]. This latter term is broader in scope, as it refers to a noncovalent interaction between any Lewis base (LB) and a chalcogen atom (Ch = S, Se, or Te) acting as a Lewis acid.

<figure><img src="image_4.png" /><figcaption>Fig. 2. A) Factors influencing the electrophilic behavior of chalcogen atoms; B) Tunable number of σ-holes and corresponding ChBs.</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>Fig. 3. Te(0)-LB1 network on Au(111) surface.</figcaption></figure>

However, the appropriate nomenclature for this class of noncovalent interactions remains a matter of debate [38,39].

The pronounced linearity of the sulfur-sulfur contacts in divalent sulfur derivatives discussed above was attributed to the participation of the σ* orbitals of the R–S and R'-S bonds [33]. The involvement of the n → σ* orbital interaction in chalcogen bonding (ChB) was later supported by theoretical studies, based on evidence from both solid-state [40] and solution-phase investigations [41]. However, the introduction of the σ-hole concept to describe noncovalent interactions involving halogen atoms [42] and its subsequent extension to the chalcogen elements [43], highlighted that electrostatic attraction can also play a key role in determining the strength of the ChB [44]. Interestingly, the linearity of the ChB can be also rationalized through the σ-hole concept. Highly polarizable and electron-rich atoms bonded to more electronegative substituents exhibit an anisotropic distribution of electron density. This anisotropy gives rise to regions of electron depletion—termed σ-holes—even in otherwise electron-rich species. Situated opposite to the covalent Ch–R σ-bonds, these σ-holes act as electrophilic sites that promote highly directional interactions with electron-density donors.

The spatial coincidence of the σ-hole with the σ* orbital makes it difficult to distinguish the charge-transfer contribution from the electrostatic one. This issue was generally addressed through theoretical energy decomposition analyses [40,45], which also highlighted the importance of dispersion forces in ChB cohesion [46,47]. The relative significance of the individual energetic components is influenced by the nature of both the chalcogen-containing derivative and the interacting LB.

Considering the three attractive energy components of the ChB, its strength can be tuned by various factors, highlighting its remarkable versatility. The electrophilicity of the chalcogen atom can be enhanced either by increasing the positive potential of its σ-holes or by lowering the energy of the corresponding σ* orbitals. These effects are typically achieved through the introduction of electron-withdrawing groups (EWG) on the chalcogen atom or by increasing its oxidation state (Fig. 2A). While divalent chalcogen derivatives can form two ChBs owing to the presence of two σ-hole, tetravalent chalcogen compounds, which possess three σ-holes, are capable of forming up to three ChBs. In contrast, hexavalent chalcogen species exhibit a single σ-hole located

opposite the apical substituent, while all other directions are sterically blocked [48] (Fig. 2B).

In the solid state, ChBs are most commonly identified and characterized by X-ray diffraction (XRD), which provides direct access to the geometric parameters of the interaction—namely, interatomic distances ($d_{Ch-LB}$) shorter than the sum of van der Waals radii and approach angles ($\theta$) typically ranging from 160 to 180° (Fig. 2B). Recent developments, however, have extended ChB characterization beyond the solid state. A range of analytical techniques—including UV-visible spectroscopy, NMR spectroscopy, IR spectroscopy and isothermal titration calorimetry (ITC)—now enable the investigation of ChBs in solution [49]. When combined with theoretical calculations, these methods make it possible to classify ChBs according to their relative strength, from weak to very strong, and help assess whether they can be regarded as coordination bonds.

### 1.3. Scope and aim of the review

Owing to the high polarizability of tellurium, compounds containing this element tend to form stronger ChBs than their selenium- and sulfur-based analogues. These species display pronounced dispersion interactions, deep σ-holes, and low-lying σ* orbitals, which collectively enhance their ability to form strong ChBs. Consequently, the incorporation of tellurium into diverse derivatives has grown significantly over the past decade. In this review, we focus on compounds bearing electrophilic tellurium centers that can form particularly stable complexes with Lewis bases. Our objective is to highlight recent advances in the field and to illustrate the versatility and potential of tellurium derivatives in diverse ChB-related applications. The discussion will encompass both solid-state and solution studies of ChB-based molecular complexes featuring tellurium in different oxidation states.

## 2. ChB-based molecular complexes involving tellurium(0)

Sun and coll. Have recently shown that 2D supramolecular organizations could be obtained by deposition on a gold surface of atomic tellurium and dinitrile LB1 [50]. This organization was proposed to be driven by the so-called "tellurium-based chalcogen organic interaction",
<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /><figcaption>Fig. 4. ChBs with ditellurides Te1 and Te2.</figcaption></figure>

that is ChBs between tellurium and the nitrogen atoms of the nitrile groups (Fig. 3). Theoretical calculations confirmed the role of electrostatic interactions in stabilizing the Te-directed molecular network. Even if the Te(0)-carbonitrile interaction exhibited lower stability than the more frequently studied Cu-carbonitrile metal-organic coordination, this methodology based on ChB represents a new approach for constructing molecular self-assembly on metal surfaces.

### 3. ChB-based molecular complexes involving Te(I) compounds: Ditellurides

Ditellurides exhibit interesting biological properties, mostly peroxidase-like catalytic activity by mimicking the action of the selenium-containing glutathione-peroxidases [51] whose mode of action could rely on ChB [52]. Two recent studies supported this possibility by confirming the ability of ditellurides to act as ChB donors. In 2022, Mamane and *coll.* showed that diarylditelluride Te1 was able to form weak ChBs in non-polar solvents with phosphine oxides [53]. The formation of the molecular complex in solution between Te1 and tributyl phosphine oxide LB2 was demonstrated by ¹⁹F-¹H HOESY (Heteronuclear Overhauser Effect Spectroscopy) experiment (Fig. 4A).

<figure><img src="image_8.png" /><figcaption>Fig. 5. Ligand stabilization of aryltellurenyl cations leading to ChB or 3c-4e bonding. Distances (in red) are given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>**Fig. 6.** Complexes of Te(II) halides and pseudohalides. Distances (in red) are given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

Shortly afterwards, Singh and coll. characterized tellurocystine hydrochloride Te2 in the solid state, showing strong ChBs between tellurium and chloride ions (Fig. 4B). A combination of surface molecular electrostatic potential (MEP) and Quantum Theory of Atom in Molecules (QTAIM) analysis proved the σ-hole nature of the interaction [54].

# 4. ChB-based molecular complexes involving Te(II) compounds

## 4.1. Tellurium halides and pseudohalides

The aryltellurenyl "ArTe" moiety is isoelectronic to iodine and exhibits similarities in reactivity and structure. Aryltellurenyl salts of general structure ArTeX are however unstable compounds and decompose at room temperature [55]. In a similar way to iodonium which can be stabilized by ligands such as pyridine to give [I(pyr)₂]⁺ [56], tellurenyl salts bearing phenyl (Te3), mesityl (Te4-Te6), 2,6-dimethylphenyl (Te7) and 2,6-dimesitylphenyl (Te8) were successfully stabilized by ligands of different nature, including Ph₃P (LB3) [57,58], Ph₃As (LB6) and Ph₃Sb (LB7) [58], imidazoline-2-selones (LB4 and LB9) [59,60], a bidentate phosphane selenide (LB5) [61], a tellane (LB8) [62] and a N-heterocyclic carbene (NHC) (LB10) [63] (Fig. 5). The coordination of these ligands LB3-LB10 to RTeX leads to Te-X bond elongation. A closer look at the X-ray structures of tellurenyl/LB

complexes showed in most cases the non-covalent nature of the Te-X bond with geometrical parameters corresponding to a ChB. However, in complexes Te3/LB3, Te4/LB4 and Te4/LB5, the iodide is still strongly bound to tellurium, suggesting a 3c-4e three-body system [60]. In contrast, the Te-I distance is longer in complex Te8/LB10, probably because of the steric hindrance imposed by the bulky mesityl groups of LB10. Interestingly, complex Te5/LB7, in which the tellurenyl cation is stabilized by a stibine ligand, exhibits an interaction between the triflate oxygen and both the tellurium atom (through ChB) and the antimony atom (through pnictogen bonding) [64].

The same ligand-based strategy was used for the stabilization of di (pseudo)halo tellurium species. The resulting liganded tellurium species represent useful stable sources of TeX₂ complexes that are otherwise unstable or do not even exist in the solid state. Various sources of Te(II) such as TeCl₂, TeI₂, Te(OTf)₂ and ClTe(OTf) could be stabilized in the presence of 1,3-dimethyl-2(3H)-imidazolethione (LB11) [65], the bidentate phosphane selenide LB5 [61], diimino ligands (LB12 and LB13) [66–68], a NHC ligand (LB14) [67], a diphosphine (LB15) [69] and 2,2'-bipyridine (LB16) [70]. With complexes of Te(II) halides TeCl₂/LB11, TeI₂/LB5 and TeI₂/LB12, much longer distances ($d_{Te-Y}$) than expected for covalent bonds were observed between Te and the interacting atoms (Y) from the ligands. This observation and the linear approach of the ligand toward Te indicated a probable involvement of
<figure><img src="image_10.png" /><figcaption>**Fig. 7.** Triazole- and triazolium-based tellanes for anion recognition. Distances (in red) are given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>**Fig. 8.** Complexes of tellanes bearing polyfluoroaromatic groups. Distances (in red) are given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

ChB. In the triflate-based complexes Te(OTf)₂/LB12, Te(OTf)₂/LB13, Te(OTf)₂/LB14, Te(OTf)₂/LB15 and ClTe(OTf)/LB16, shorter distances ($d_{Te-γ}$) were observed, likely due to a the weaker interaction between Te and the triflate ion compared to chlorine and iodine. In these cases, the triflate ion appears to interact with Te through ChB (Fig. 6).

## 4.2. Tellanes

Several strategies have been employed to enhance the σ-hole intensity of tellurium in tellane derivatives. The most common approach involves introducing one or two electron-withdrawing groups (EWG) on the tellurium atom, thereby activating one or both Te σ-hole(s) of the tellanes.
<figure><img src="image_12.png" /><figcaption>**Fig. 9.** Alkynyl- and icosahedral carborane-based tellanes. Distances (in red) are given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

Triazole-based tellanes constitutes a broad family of ChB donors in which the electrophilicity of tellurium arises mainly from the electron-withdrawing character of the triazole ring. However, the triazole ring itself is not sufficient to promote strong ChB; therefore, different strategies based on cooperativity [71] and on additional activation of Te σ-holes have been used to make the triazole-based tellanes effective in ChB applications. The introduction of other EWGs on the triazole structure and/or the use of crown ethers whose electron-withdrawing ability could be switched on by complexation of cations were shown to be very efficient methods to increase the anion binding of these tellurium motifs [72–75]. The resulting complexes were identified in solution by NMR and Isothermal Titration Calorimetry (ITC), and in the solid state by XRD. ChB involving tellurium atoms of the bidendate tellane **Te9** and different anions as well as coordination of the cation to the crown ether could be clearly observed in different complexes such as **Te9/KBr** [74] and **Te9/NH₄Br** [75] (Fig. 7). N-Alkylation of the triazole ring is another convenient way to increase its electron-withdrawing ability, thus rendering the tellurium much more positive. This strategy was used for the design of efficient bidentate Te-based catalysts [76,77]. By using the photoswitchable azo-based tellane **Te10**, the cooperativity of the two tellurium atoms to bind halides was shown to be the key parameter for their high reactivity. Indeed, the Z isomer has higher association constant for halide anions than the E isomer [78] (Fig. 7).

The introduction of two highly electron-deficient polyfluoroaromatic groups on tellurium could generate tellanes **Te11** and **Te12** with excellent ChB donor properties. The latter were used as electrophilic ligands of platinum complexes **Pt1** and **Pt2** to provide chalcogen-bonded complexes **Te11/Pt1**, **Te12/Pt2** and **Te12/Pt2** [79,80]. Interestingly, with dithiocarbamate complex **Pt2**, an unusual three-center Te··(Pt,S) ChB was observed [80]. Tellanes **Te11** and **Te12** were also described to form multiple ChBs with dichalcogenides **LB17** (Ch = Se) and **LB18** (Ch = Te) leading to supramolecular assemblies in the solid state [81] (Fig. 8).

With the aim of building supramolecular networks with tellane ChB donors, an elegant strategy relying on the selective activation of one σ-hole over the two Te-centered σ-holes was proposed [5]. This strategy enabled control over the directionality of ChB between properly designed tellanes and LBs. In this regard, alkynyltellanes **Te13** and **Te14** whose activation of the σ-hole in the prolongation of the (C≡)C–Te bond formed strong ChBs in the solid state with **LB19** to provide the 1D extended structure **Te13/LB19** [82] or with **LB20** to form the supramolecular rectangle **Te14/LB20** [83]. In a similar way, the icosahedral borane group was also able to activate the σ-hole in the prolongation of the (carborane)C–Te bond. The bis-tellane **Te15** was thus designed and could lead to the 1D supramolecular zig-zag chain **Te15/Cl**- in the presence of chlorides [84] (Fig. 9).
<figure><img src="image_13.png" /></figure>

$$K_a(\text{THF}) = 2290 \text{ M}^{-1}$$

<figure><img src="image_14.png" /></figure>

$$K_a(\text{THF}) = 51 \text{ M}^{-1}$$

$$K_a(\text{THF}) = 78 \text{ M}^{-1}$$

<figure><img src="image_15.png" /><figcaption>Fig. 11. ChB involving the Te₂N₂ system in telluradiazoles **Te18** and **Te19**. Distances (in red) are given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

### 4.3. Tellurophenes

The anion recognition ability of two structurally similar electron-deficient bidendate tellurophenes **Te16** and **Te17** was studied in solution. The association constants ($K_a$) of **Te16** with different anions X⁻ were measured by UV-Vis spectroscopy, revealing the strongest binding with chlorides, consistent with bidentate anion coordination through two Te···Cl- ChBs [85]. A much lower $K_a$ value was obtained by NMR for chlorine binding to **Te17**. As shown through theoretical calculations, tellurophene **Te17** failed to behave as a bidendate ChB donor because of its structural deformation upon anion chelation. Instead, **Te17** was shown to be able to bind the chloride anion through a combination of HB and ChB from the same tellurophene ring. These calculations are thus in agreement with the experimental results showing that the monotellurophene derivative **Te18** binds more strongly to Cl⁻ than **Te17** [86] (Fig. 10).

### 4.4. Tellurium-based azoles

Electron-poor tellurium compounds such as tellurazoles,

telluradiazoles and isotellurazole oxides were described to self-assemble in the solid-state and in solution through Te···N and Te···O ChBs [87–92]. With telluradiazoles **Te18** and **Te19**, even the addition of LBs such as DMSO (**LB21**) and pyridine (**LB16**) did not disrupt the dimeric Te₂N₂ structure. In these cases, dimeric complexes **Te18/LB21** and **Te19/LB22** were isolated, showing respectively Te···O and Te···N ChBs [93,94] (Fig. 11).

In contrast, the Te₂N₂ structure was not observed with telluradiazole **Te20** in association with LBs. A series of chalcogen-bonded complexes **Te20/X⁻** was obtained by crystallization of **Te20** in the presence of different anionic species such as Br⁻ [95], PhS⁻ [96] and NC–O⁻ [97]. Neutral LBs were also found to form stable ChB complexes with **Te20** in the solid state, as confirmed by XRD and solid-state NMR spectroscopy. The ditopic 1,4-diazabicyclo[2.2.2]octane (**LB23**) formed complex **Te20/LB23** with a zig-zag 1D structure [98] whereas the discrete complexes **Te20/LB22** and **Te20/LB24** were isolated by using pyridine (**LB22**) [95] and its corresponding N-oxide (**LB24**) [99]. The use of the pyridine oxide **LB25** delivered the complex **Te20/LB25** showing an uncommon spiral shape [99]. Finally, the cyclic polyether 18-crown-6 (**LB26**) behaved as a ditopic LB since two directional Te···O ChBs
<figure><img src="image_16.png" /><figcaption>**Fig. 12.** ChB involving telluradiazoles **Te20** and **Te21**. Distances (in red) are given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

could be detected in the solid state in the complex **Te20/LB26** [100]. Benzotelluradiazole **Te21** have been designed to track alterations in their UV-vis absorbance or emission spectra upon ChB in solution. Addition of increasing amount of chloride anions to **Te21** in THF solution induced a bathochromic shift allowing to determine a $K_a$ of 970 M⁻¹. This value was shown to vary with the nature of the benzotelluradiazole substituents and the solvent [101] (Fig. 12).

In the case of isotellurazoles N-oxides, the disruption of their self-assembly was induced by the addition of Lewis acids which strongly bind to the oxygen. Thus, the reaction of **Te22** with **BF₃** furnished **Te22-BF₃** adduct which after addition of **LBs** such as DMAP (**LB27**) and NHC **LB28** delivered complexes **Te22-BF₃/LB27** and **Te22BF₃/LB28** [102] (Fig. 13).

The nature of the strong ChB between tellurium-based azoles and **LBs**

was analyzed by SAPT (symmetry adapted intermolecular perturbation theory) calculations showing that these attractive interactions are dominated by the electrostatic and the induction (polarization and charge transfer) term. Importantly, these calculations demonstrated that the assembly of the atoms involved in the ChB is directed by steric interactions, thus explaining the deviation from linearity observed in some cases [103].

### 4.5. Other Te(II) systems

The tellurium analogue of tetrathiafulvalene **Te23** was shown to be engaged in Te···N intermolecular interactions with tetracyanoquinodimethane **LB29**. These interactions, which exhibit the characteristic geometrical parameters of ChBs, were proposed to be at the origin of the
<figure><img src="image_17.png" /><figcaption>**Fig. 13.** Discrete ChB complexes based on $Te_{22-BF_3}$. Distances (in red) are given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

<figure><img src="image_18.png" /><figcaption>**Fig. 14.** ChBs between $Te_{23}$ and $LB_{29}$. Distances (in red) are given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

higher electrical conductivity of $Te_{23}$ compared to its lighter sulfur- and selenium-containing analogues [104] (Fig. 14).

# 5. ChB-based molecular complexes involving Te(IV) compounds

## 5.1. *Tellurium catecholates*

The synthesis of the first bis(catecholato)-tellurium (IV) complex was described by Antikainen and Mälkönen in 1959 [105]. However, it was only in 1967 that Lindqvist solved the first crystallographic structure of a tellurium (IV) catecholate **Te24** [106] (Fig. 15). The geometry of such complex consists of a seesaw-like structure, with the tellurium center coordinated by two oxygens in axial positions and two in the equatorial plane. Therefore, this structure can also be considered as distorted trigonal bipyramidal geometry, with an $O_{ax}$-Te-O$_{ax}$ angle of 154° and where the equatorial plane is occupied by the two remaining

oxygens and tellurium lone electron pair. Interestingly, this crystallographic structure demonstrated the presence of a weak intermolecular interaction between one of the axial oxygens and a neighboring tellurium atom. This noncovalent interaction leads to the formation of polymeric rows of tellurium catecholate molecules in the solid state. However, the $O_{ax}$-Te-O$_{eq}$ angle of 153.7° somewhat diverges from the 180° expected for a ChB. Further crystallographic and theoretical investigations have demonstrated that the Te—O bond possesses a predominantly covalent character, with bond orders slightly below unity and bond lengths of approximately 2 Å [107].

Tuck and *coll*. Explored the direct synthesis of Te (IV) catecholates by the oxidation of elemental tellurium with *ortho*-benzoquinones [108]. Further studies on the resulting bis(catecholato) tellurium derivatives revealed that they were highly resistant to further oxidation from strong oxidizing agents such as bromine or iodine. Notably, these findings shed light upon the coordination chemistry of this family of compounds, as
<figure><img src="image_19.png" /><figcaption>**Fig. 15.** Complexes of Te-catecholate **Te24-Te26**. Distances (in red) are given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

can be seen by the formation of 1:1 adducts between derivatives **Te25-Te26** and a series of Lewis bases. These efforts allowed the crystallographic characterization of two of these adducts, specifically those involving an intermolecular interaction with 2,2'-bipyridine (**LB16**) and the crown ether **LB26** (Fig. 15). **LB16** interacts with the tellurium center of **Te25** in a somewhat distorted manner, with N-Te-Oeq angles closer to 150°, as can be expected given the steric constraints of the bipyridine ligand. The Te···N distances in the case of complex **Te25/LB16** are

relatively short compared to those measured for the complex **Te26/LB26**, where the Te···O distances are strikingly long (ranging from 2.980 to 3.517 Å). The geometric distortion of the cyclic ether is consistent with that observed with other crown ether complexes of Bi(III) and Sb (III) [109], providing further evidence for the existence of a stereochemically active lone pair of electrons. This conclusion is supported by the large and seemingly empty region of space surrounding the tellurium center in complex **Te25/LB16**.

<figure><img src="image_20.png" /><figcaption>**Fig. 16.** Te(IV)-catecholate complexes involving O- and N-based ligands. Distances (in red) are given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>
<figure><img src="image_21.png" /><figcaption>**Fig. 17.** Complexes involving Te(IV) halides. Distances (in red) are given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

With the goal of investigating new recycling and separation methods for tellurium-containing photovoltaic waste materials, Bart and coll. delved into the study of the redox properties of Te24 and Te26 with organic oxidizing agents [107]. For example, the reaction between various Te (IV) catecholates and pyridine-N-oxide (LB24) or N-methyl-morpholine-N-oxide (NMO, LB30) led to the corresponding 1:1 ChB complexes Te24/LB24 and Te26/LB30 (Fig. 15). In contrast to those with bidentate Lewis bases, these N-oxide complexes display a relatively short Te—O distance and an interaction angle closer to 180°. Further evidence of the ChB lies on the lengthening of the N—O bond relative to the free N-oxides. Attempts to study the strength of the N—O bond by FT-IR showed insignificant changes in the vibrational frequency for such bond in the case of NMO complexes such as Te26/LB30. However, pyridine N-oxides manifested an approximate shift of 40 cm⁻¹ of the N—O frequency toward lower energy vibrations, consistent with the lengthening of the N—O bond.

More recently, the study of tellurium catecholates with various ethers was also pursued by Petrov, yielding three new crystallographic structures of tellurium complexes with various ethers [110]. The author demonstrated a high versatility of coordination modes that both cyclic and acyclic ethers can adopt in the vicinity of the electrophilic tellurium center. For instance, the 1:1 adduct of Te27 with glyme (dimethoxy-ethane, LB31) led to the formation of a dimer where the tellurium atom is coordinated by four oxygens (Fig. 16). Surprisingly, the use of crown ether LB26 as a Lewis base gave the 2:1 adduct (Te27)₂/LB26, in which two Te catecholates are coordinated by a single 18C6 molecule (Fig. 16). Although the Te···O distances are far from homogeneous, the four shortest contacts correspond to interactions with geometric parameters closer to those expected for a ChB.

The sterically congested Te27 was subsequently employed for the synthesis of adducts with numerous oxygen and nitrogen-based Lewis bases [111,112]. In the presence of common solvents such as acetone (LB32), DMF and some substituted pyridines, the formation of dimeric solvates is favored, as can be seen with Te27/LB32 (Fig. 16), where each lone pair of acetone oxygen atom interacts via ChB with two tellurium

centers. More importantly, the authors described a unique bipyridine µ-κ²N,N'-κ²N,N' bridging coordination mode, as can be found in the centrosymmetric Te27/LB16. Even though each bipyridine ligand is more tightly bound to one of the two tellurium centers, two additional contacts are also observed between the two nitrogen atoms and the neighboring tellurium atom (not shown). DFT calculations and QTAIM analysis estimate the strength of these weak interactions to be 2.2 and 0.9 kcal/mol. As it had been previously rationalized computationally in a similar Te catecholate complex [107], the Te lone pair is energetically buried below the HOMO of the complex, explaining its apparent neutrality toward direct oxidation. In fact, the use of strong oxidizing agents such as PhI(OAc)₂ led to the oxidation of the ligand to its corresponding free quinone (3,6-di-tert-butyl-1,2-benzoquinone), rather than forming a Te(VI) derivative.

Other N-donor Lewis bases such as diamine, terpyridine and 2,2'-bipyrimide were described to form complexes with Te27 [113]. Quite interestingly, the use of N,N'-dimesitylethanediimine (LB33) yielded an infinite chain organized in a zig-zag manner (Fig. 16) where the ligand adopts a bridging µ-κ¹N:κ¹N' coordination mode. DFT calculations based on the crystallographic structures imply that the Te···N interactions are weak and completely non-covalent. This conclusion is supported by the absence of any new band in the UV–vis-NIR spectra of these complexes, suggesting the lack of ligand-to-ligand charge transfer from the catecholate to the N-based ligand.

## 5.2. Tellurium halides

The Te-X bond in tellurium tetrahalides exhibits a continuum from covalent to ionic character. For instance, tellurium tetrachloride is predominantly covalent in the vapor state [114], yet it can be readily ionized in solution [115].

The coordination behavior of Te(IV) halides is influenced by the presence of Lewis bases, with the resulting adducts typically adopting octahedral geometries [116]. The reaction of TeCl₄ with two equivalents of OPPh₃ (LB34) leads to the formation of complex TeCl₄/LB34 where
<figure><img src="image_22.png" /><figcaption>**Fig. 18.** Te(IV) halide complexes with S- and N-based ligands. Distances (in red) are given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

the two ligands occupy a cis equatorial position. This mode of coordination clearly reveals the presence of ChB interactions, as both Lewis bases interact with the Te(IV) center opposite to two equatorial chlorine atoms with an interaction angle close to 180° (Fig. 17). Further studies explored the use of phosphine chalcogenides as neutral ligands, yielding the brominated complexes which displayed highly similar geometric parameters [117]. The IR analysis of these complexes showed diminished P=O vibration frequencies relative to those in the free ligand. Quite intriguingly, the ¹²⁵Te NMR spectra for this family of complexes displayed no visible splitting resulting from Te-P long distance coupling. The use of bidentate ligands LB35 and LB36 afforded respectively complexes TeCl₄/LB35 and TeCl₄/LB36 where the ligand behaves as a chelate, imposing a distorted octahedral geometry to the tellurium center. In the case of complex TeCl₄/LB35, the Te-chalcogenide distance is significantly shorter than in TeCl₄/LB36, revealing that phosphine oxides are stronger binders relative to phosphine sulfides [117]. In complex TeCl₄/LB36, a slight distortion from linearity compared to TeCl₄/LB35 was noted, probably due to ring strain from the chelate ligand [116]. It is interesting to note that in both cases, the equatorial Te-Cl bonds are shorter than the axial ones (Fig. 17). Furthermore, using the bidentate chalcogenide ligand LB37, which contain one additional methylene group compared to LB36, led to the formation of a complex containing a planar tellurium cation (not shown), together with a [(TeCl₅)₂/LB37] anion. In this anion, the ligand adopts a bridging coordination mode between two Te centers. This mode of coordination from bidentate phosphine sulfides is not unprecedented, as several examples have been reported previously [118,119] (Fig. 17).

Another example of ChB in Te(IV) halides involves the interaction of triphenyltelluronium tellurolate Te28 (Fig. 17) [120]. At the solid state, the tellurolate anion is surrounded by four iodine atoms, as well as the 4-pyridyl moiety in a distorted octahedron. More importantly, this salt forms a supramolecular network, in which the pyridine interacts via ChB in a perfectly linear manner with another tellurium (IV) center opposite to the Te-C bond. Interestingly, each individual tellurolate interacts with two neighboring tellurium cations by ChB via two of its iodine atoms, allowing the formation of a linear row of anionic tellurolate anions along the crystallographic *a* axis.

A rare example of mixed-valence co-crystal was reported, in which the Te(IV) center is involved in a ChB with an adjacent phenyltellurium (II) iodide (Te29), which is itself stabilized through a ChB with a thio-urea molecule (LB38) [121] (Fig. 17). In the solid state, this complex exists in a tetrameric structure, in which the Te(IV) center is bound to a neighboring iodine by a longer, yet highly directional ChB. A more detailed study of this structure was carried out by Tiekink and coll., [122] whose computational calculations gave MEP (Molecular Electrostatic Potential) values for the σ-holes of both the Te(IV) (40.2 kcal/mol

and 26.3 kcal/mol for σ-holes opposite to the Te-I and Te-C bonds, respectively) and Te(II) centers (9.4 kcal/mol at the antipode of the Te-C bond). Moreover, QTAIM analysis gives a negative total density value (H = -0.0028 a.u.), as well as an important charge density (0.0293 a.u.) for the short Te(IV)-I bond, revealing a strongly covalent character. NBO (Natural Bond Orbital) studies confirm such conclusion, by attributing an important Lone-Pair-to-σ*(Te(IV)-I) charge transfer, corresponding to a stabilization energy of 77.5 kcal/mol.

Direct coordination of a thiourea ligand to a phenyltellurium(IV) trihalide has also been portrayed in the literature [123,124], but it was only until the full crystallographic studies of Schutz Lang and coll. [125] that it could be ascertained that such complexes share a high similarity to the aforementioned example (see for example Te30/LB39, Fig. 18). Namely, the thiourea ligand adopts the same equatorial coordination mode around the Te(IV) center and the dimeric structure is held together by intermolecular ChBs between a neighboring halide and the σ-hole at the antipode of the Te-C bond. Thioethers are another class of weakly-binding ligands, that are known to react with TeX₄ (X = Cl or Br) to form relatively stable adducts, allowing proper crystallographic characterization [126]. In the presence of bidentate dithioether ligands LB40, Te (IV) halides form cis-octahedral monomers such as complex TeCl₄/LB40, in which each sulfur atom is bonded via ChB to the tellurium center opposite to the equatorial Te-Cl bond. Quite interestingly, the use of the monodentate thioether dimethylsulfide (LB41) leads to the formation of binuclear complex TeCl₄/LB41, featuring two µ-Cl bridging ligands, and where the thioether ligands are located in an apical orientation. Variable-temperature ¹²⁵Te NMR characterization of these complexes shed light upon the highly dynamic nature of the Te-SR₂ interaction in solution, which is consistent with the properties expected for a Te(IV) adduct with a weak σ-donor ligand.

As described with the previous examples, the octahedral structure of these adducts demonstrate the absence of a stereochemically relevant nonbonding electron pair from the Te(IV) atom. Consequently, the geometric distortions from perfect octahedral geometry can better be explained by a 3c-4e bond between the tellurium center and two halide atoms. This approach is consistent with the assumption that the nonbonding electron pairs are mainly located in the s-orbital of tellurium valence shell.

Tellurium (IV) halides are also known to form coordination complexes with various N-donor neutral ligands (see for example TeX₄/LB42 and Te31/LB43, Fig. 18). In fact, several examples of complexes with nitrogen-based ligands have already been reported by Verma and coll. [124,127-130], and Couch and coll. [115] (Fig. 18). The study of molar conductance, along with IR characterization, shed light upon the formation of these 1:1 adducts in solution. However, the absence of further structural information by crystallography precludes us from
<figure><img src="image_23.png" /></figure>

<figure><img src="image_24.png" /></figure>

<figure><img src="image_25.png" /><figcaption>**Fig. 19.** Crystallographic structures depicting telluronium cations interacting with their respective anion (Te31, Te32) and neighboring Lewis basic moieties (Te33). Distances (in red) are given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

<figure><img src="image_26.png" /><figcaption>**Fig. 20.** Selected examples of telluronium solvates. Distances (in red) are given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

verifying if such interactions comply with the geometric parameters of a ChB. However, despite these limitations, one can expect these types of complexes to adopt a pseudo-octahedral geometry, with the bidentate ligand occupying a cis-equatorial configuration as seen in the previous examples. The coordination of Te(IV) halides was briefly discussed by Ragogna and *coll.* who provided the crystallographic structure of the complex of TeBr₄ with the bulky diimine **LB44**. Quite surprisingly, the Se-based analogous complex was not obtained from direct reaction between SeBr₄ with **LB44**, as selenium halides undergo a two-electron reduction, followed by the release of Br₂ forming a rather rare 1,2,5-seleniadiazolium cation [131].

### 5.3. Telluronium cations

Telluronium salts are molecular cations of structure [TeR₁R₂R₃]⁺X⁻, in which the central tellurium atom is bonded to three substituents and possesses three σ-holes. The tellurium center exhibits a hypervalent (tetracoordinate) character, carrying a net positive charge that is neutralized by the corresponding anion (X⁻). These σ-holes readily engage in interactions with electron-density donors, as evidenced by numerous crystallographic data showing close contacts between tellurium cations and their respective anions [132].

This behavior in the solid state is illustrated by the crystallographic structures reported by Collins and *coll.* [133] (see **Te31** with Cl⁻, Fig. 19) and Klapötke and *coll.* (see **Te32** with NC-O-, Fig. 19) [134], in which the telluronium cation interacts through ChB with three neighboring anions via its corresponding σ-holes, leading to an AX₃Y₃E geometry. These interactions can also be intramolecular, as illustrated by the structure recently reported by You and *coll.* (see **Te33**, Fig. 19) [135] where the metalloid interacts with two triflate anions and intramolecularly with a nonbonding electron pair from a neighboring aldehyde moiety.

To elucidate the role of ChB in such cation-anion pairs, a recent theoretical investigation analyzed approximately one thousand crystal structures from the CSD database [132]. The study revealed that these interactions are directional in both the solid state and the gas phase, with heavier ChBs forming bonds of greater covalent content. Energy decomposition analysis further indicated that the orbital component contributes significantly to the attractive nature of ChBs between cations and anions. Consequently, non-coordinating anions are highly desirable

<figure><img src="image_27.png" /><figcaption>**Fig. 21.** A) Lewis-acidic bidentate ligand **Te35** used for selective fluoride binding. B) First example of a telluronium cation **Te36** behaving as a σ-acceptor ligand. Distances (in red) are given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>
<figure><img src="image_28.png" /><figcaption>Fig. 22. Chloride affinity of tellurium cations in solution.</figcaption></figure>

for solution-phase processes, particularly in catalysis [2,3].

The ChB between tellurium and the anion is nearly omnipresent among tellurium salts in the solid state; therefore, in this part, we will not further explore these interactions and focus only on the ChB with external Lewis bases.

Other early evidence of the propensity of tellurium cations to establish ChBs with Lewis bases involves the crystallographic characterization of solvates. This can be illustrated by the crystallographic structure of the solvate between tris(trifluoromethyl)tellurium fluoride Te34 and DMF (LB45) (see Te34/LB45, Fig. 20) [136]. As for the previous examples, the tellurium center adopts a pseudo-octahedral geometry, where two fluorides and one molecule of DMF interact with the metalloid center by ChB. The oxygen atoms of both ethers establish noncovalent interactions, as can be deduced from Te···O bond lengths situated below the sum of the van der Waals radii of both atoms. The crystal structure of triphenyltellurium chloride Te31 described by Zhang and coll. displays yet another interesting example, where a molecule of acetic acid (LB46) acts as a bridging ligand to two tellurium cations via ChB, allowing the formation of a dimeric structure (Te31/LB46) further reinforced by two μ-bridging chlorides engaged in ChBs with the two Te centers (Fig. 20) [137].

All the previously mentioned examples constitute mere evidence of the inclination of telluriums to behave as highly electrophilic entities in the solid state. However, as the interest in these chalcogen-based anions grew overtime, new potential applications began to be discovered in the last years. A relatively early example of a potential application of ChB in tellurium salts was described by Zhou and Gabbaï in 2010, with the synthesis of a Lewis-basic bidentate ligand capable of selectively binding fluoride anions (Fig. 21A) [138]. Upon introduction of KF in methanol, compound Te35 establishes a cooperative binding of fluoride between the borane and the tellurium center, as it was confirmed by multinuclear ¹⁹F, ¹¹B and ¹²⁵Te NMR experiments. Namely, the ¹²⁵Te spectra of Te35/F⁻ displays a split signal for the tellurium center, corresponding to a Te—F coupling (¹J<sub>Te-F</sub> = 940 Hz), a phenomenon often observed within fluorine-containing organotellurium derivatives [139]. Furthermore, UV-visible titration of the tellurium borane in methanol suggests the formation of a discrete 1:1 adduct with an associated binding constant of 750 M⁻¹. Additionally, the crystal structures of Te35/F⁻ confirmed the formation of a ChB, as can be deduced from the near-to-linear F-Te-C angle, and a close contact between Te and F. An NBO analysis on a DFT-optimized structure of Te35/F⁻ revealed the presence of two lp(F) → σ*<sub>Te-C</sub> donor-acceptor interactions.

In a similar approach, Lin and Gabbaï, who had previously studied

the reversible two-electron processes in Te—Pt containing complexes [140], delved into the potential use of tellurium cations as σ-acceptor ligands [141]. Their research led to the synthesis of the Te36/PdCl2 complex (Fig. 21B). This binuclear species displays a tellurium cation engaged in a Te—Pd bond, whose analysis by PML (Pipek-Mezey localization analysis) and NBO revealed a highly polarized bond, resulting from a Pd → Te donor-acceptor interaction between a d orbital from the Pd(II) center and the σ*<sub>Te-O</sub> orbital. This represents the first example of an electrophilic tellurium cation behaving as a Z-type ligand toward a transition metal. More importantly, the crystallographic structure of such complex reveals a tellurium center adopting a seesaw geometry, consistent with the interaction of the palladium atom with the σ-hole of the Te-OH bond, in agreement with the geometric parameters expected for a ChB.

The Lewis acidity of tellurium cations was also exploited by Zhou and Gabbaï for the preparation of transmembrane anion transporters [142]. The oxidative methylation of diaryltellurides bearing electron-withdrawing aryl groups was employed as a way of increasing the ChB donor properties of the tellurium, thus making it more electrophilic by lowering the energy of the σ*<sub>Te-C</sub> orbitals, associated with a deepening of the corresponding σ-holes. These species were used as hosts for chloride anions, whose binding to the tellurium center via ChB was characterized in solution through ¹⁹F NMR titration. This analysis revealed that the most Lewis acidic tellurium salt Te37 could bind up to two chloride anions by ChB. The strong binding affinity of these compounds was further supported by their high performance in promoting chloride efflux from unilamellar vesicles (Fig. 22A).

The idea of halogen sequestration was subsequently pursued by Zhou and Gabbaï for the conception of tellurium-based Lewis acids capable of carrying out halogen abstractions, with potential applications as catalyst activators [143]. Computational studies performed on tellurium salt Te38 (Fig. 22B) revealed the presence of a pocket of positive electrostatic potential situated between the two tellurium cations, as well as LUMOs with important contributions from the σ*<sub>Te-C</sub> orbitals. These characteristics favored the affinity of Te38 for a single chloride anion, as it was demonstrated by the ability of this dication to perform halogen abstraction from trityl chloride. This interesting property was then employed experimentally to perform chloride abstraction from gold and palladium complexes, leading to cationic catalysts with high catalytic activity in cycloisomerization reactions.

Our group also delved into the potential of tellurium cations in catalytic systems, in which their high electrophilicity could be used to catalyze reactions commonly promoted by Lewis acids [144]. As pointed out by Gabbaï, methylation of diaryltellurides proved to be a rapid
<figure><img src="image_29.png" /><figcaption>Fig. 23. Stability of complex Te39/LB34 in solution.</figcaption></figure>

access to methyltellurium salts allowing the synthesis of four structurally different tellurium cations, with varying counter-ions. These species display three distinct σ-holes, a characteristic that was pointed out by DFT calculations (Fig. 2B). A series of NMR experiments in 1:1 mixtures of the BaRf<sub>24</sub> (tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) tellurium Te39 with <sup>17</sup>O-labelled Ph<sub>3</sub>PO (LB34) allowed a multinuclear NMR study of the association of the two species in solution, resulting in notable chemical shift variation in <sup>17</sup>O, <sup>31</sup>P and <sup>125</sup>Te NMR signals. The formation of complex Te39/LB34 in solution was also confirmed by NOESY experiments, that unveil a correlation between the o-protons from Ph<sub>3</sub>PO with both the methyl and o-protons of the tellurium cation (Fig. 23A). The stability and formation of such adduct was also confirmed by the ESI mass spectrum of Te39/LB34, yielding an isotopic distribution coherent with the formation of a 1:1 adduct (Fig. 23B). Notably, tellurium salt Te39 displayed important catalytic activity and was able to promote the catalytic activation of N-bromosuccinimide (NBS) in the bromination of anisole and bromolactonisation reactions. Catalyst Te39 was also able to activate diarylimines in the aza-Diels-Alder reaction with a diene.

More recently, an in-depth study of the chalcogen-bonding capacity of methyldiaryltellurium species such as Te39 was carried out by our group [145]. In an experimental and theoretical joint study, we explored the affinity of various diarylmethyltellurium cations with diverse Lewis bases. The analysis of 21 crystal structures of diarylmethyltellurium salts provided evidence that the σ-holes interact in a highly directional manner with ChB acceptors (usually their corresponding counter-ion) in 88 % of cases. The combined use of DOSY (Diffusion Ordered SpectroscopY) NMR and ITC (Isothermal Titration Calorimetry) experiments allowed the identification and thermodynamic characterization in solution of the 1:1 tellurium-OPPh<sub>3</sub> association (K<sub>a</sub> = 7.10<sup>3</sup> M<sup>-1</sup> in dichloromethane) and the 1:2 association (K<sub>a</sub> = 9.10<sup>2</sup> M<sup>-1</sup> in dichloromethane). The data collected from ITC experiments for different diarylmethyltellurium salts with neutral Lewis bases indicated that the electrophilicity of the tellurium cation is highly dependent on the presence of electron-withdrawing groups in the aryl groups, as well as the coordinating capacity of the counter-ion. This is in fact supported by higher molar heats of interactions recorded upon the interaction of BaRf<sub>24</sub>-containing tellurium salts relative to those displaying highly coordinating counter-ions. The latter statement suggests that the association of tellurium cations with neutral Lewis bases is driven by Coulombic attraction, as it was further confirmed by IGM and IQA analyses, that finally indicated the relatively low contribution of charge transfer involved in this type of interactions.

<figure><img src="image_30.png" /><figcaption>Fig. 24. Complexes of Te40 with acetone (LB21) and imine LB47. BaRf<sub>24</sub> anion was removed for clarity; distance (in red) is given in Å. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

The capacity of telluriums to activate imines was subsequently investigated by our group [146], evidencing that methyl tellurium salt Te39 could catalyze the cyclocondensation of arylimines with alkenes. These findings paved the way for the development of a new class of Lewis acidic triaryltellurium cations, which exhibit greater stability than their methyltellurium analogues, the latter being in some cases susceptible to reductive demethylation. The most active catalyst of this series, triaryl tellurium Te40 was co-crystallized with acetone (LB21) revealing its capacity to act as ChB donor in the presence of a Lewis base (Fig. 24A). The formation of Te···N ChB was subsequently confirmed by NMR experiments revealing a significant shift of <sup>1</sup>H NMR signals of N-phenyl phenylmethanimine (LB47) in the presence of Te40. Building upon this behavior in solution, <sup>125</sup>Te NMR titration of Te40 with LB47 then yielded an association constant value of about 22 M<sup>-1</sup> in dichloromethane for the complex Te40/LB47 (Fig. 24B).

Further studies involving tellurium salt Te40 revealed that this compound could establish ChB interactions with different N-halosuccinimides: N-chlorosuccinimide (NCS, LB48), NBS (LB49) and N-iodosuccinimide (NIS, LB50) [147]. Such interactions were characterized in the solid state by the cocrystallization of each halosuccinimide with Te40 in dichloroethane. These X-ray diffraction structures shed light upon a highly directional ChB between the tellurium center and the carbonyl moiety of the corresponding halosuccinimide, as shown in the different complexes Te40/LB48, Te40/LB49 and Te40/LB50 (Fig. 25A). Moreover, a significant shift of <sup>125</sup>Te signal of Te40 in the presence of NBS was yet another proof of the ChB interaction in solution,
<figure><img src="image_31.png" /><figcaption>Fig. 25. Te40-based Complexes.</figcaption></figure>

allowing NMR titration that gave a 1:1 association constant of 17.3 M⁻¹ in dichloromethane. More interestingly, tellurium salt **Te40** proved to be a good catalyst for reactions involving electrophilic bromination, such as the aromatic halogenation of substituted arenes, as well as the haloesterification and haloalkoxylation of both cyclic and open alkenes.

Very recently, our group carried out an experimental and theoretical study on the selective binding of tellurium cation **Te40** with ChB acceptors [148]. This endeavor surprisingly led to the selective isolation and characterization of mono-, bis- and tris- adducts of **Te40** with Ph₃PO(LB34) (Fig. 25B). Despite what was previously observed with diarylmethyltellurium **Te39**, the thermodynamic parameters for each

association process with **LB34** could be determined by ITC experiments in dichloroethane (Kₐ₁ = 48.10⁴ M⁻¹, Kₐ₂ = 24.10³ M⁻¹ and Kₐ₃ = 5.10² M⁻¹) which ultimately confirmed the superior electrophilicity of **Te40** relative to **Te39**, as well as the fact that each association process with the tellurium sequentially diminishes the electrophilicity of the remaining Te σ-holes. DFT analysis underscored yet again the importance of Coulombic components in the Te-OPR₃ interactions relative to covalent ones, as well as the non-innocent role the BArF₂₄ anion in the thermodynamics of the interaction.

<figure><img src="image_32.png" /><figcaption>Fig. 26. Crystal (A) and chemical (B) structures of telluroxane cluster **Te41**. C) Simplified representation of the telluroxane halide core.</figcaption></figure>
<figure><img src="image_33.png" /><figcaption>**Fig. 27.** Chemical structure of telluroxane/selenonium macrocycles (A) and XRD structure of macrocycle **Te42** (B: top view, C: side view).</figcaption></figure>

## 5.4. Telluroxides

Telluroxides are another type of Te(IV) compounds, of chemical formula (R₁R₂Te=O) that have found potential applications in various fields, such as supramolecular chemistry, ion transport and even catalysis. A compelling example of the capacity of telluroxides to form supramolecular assemblies was described in 2023 by Beer and *coll.* In their studies, they described the preparation of organotelluroxane molecular clusters of formula Ar₁₆Te₈O₆X₄ with X = Cl, Br [149]. These structures could be obtained by the hydrolysis of the corresponding tellurium halide (R₁R₂TeX₂) in the presence of an excess of halide anions as templating agents. The chloride cluster of this family (**Te41**) was characterized by XRD, revealing a discrete supramolecular adduct held together by Te···Cl ChBs (Fig. 26). Interestingly, this structure displays two distinct oligomeric tellurane chains capped at each end by two telluronium moieties. These two oligomeric chains then interact with each other in a seemingly equatorial plane by a series of Cl-Te-Cl ChBs.

The crystallographic structure reveals that the hydrophilic interior of the telluroxane core is surrounded by a hydrophobic exterior arising from the aromatic substituents of the tellurium centers, which grants high solubility in apolar organic solvents. More importantly, these organotelluroxane clusters tend to aggregate in organic solvents upon the addition of water, leading to an aggregation induced emission process (AIE).

Very recently, Wang and *coll.* unveiled an impressive example of catalytically active mixed telluroxane/selenonium macrocycles [150]. Among the eight macrocycles synthesized, compound **Te42** could successfully be crystallized and analyzed by XRD (Fig. 27A). This compound bears two endocyclic selenonium cations, with the corresponding

triflate counterions located above and below the plane of the macro-cycle. Each sulfonate interacts tightly with four tellurium centers via two of its oxygen atoms via ChB (Fig. 27B-C). The corresponding Te···O distances range from 3.00 to 3.15 Å, well below the sum of the van der Waals radii, and the C-Te-O angles lie between 155.8° and 164.4°. It is important to point out that despite the presence of electrophilic selenonium cations, triflate anions seem to bind preferentially to the Te(IV) centers, emphasizing the increased chalcogen-binding capacity of tellurium relative to its lighter chalcogen counterparts. The authors demonstrated that macrocycles such as **Te43**, endowed with the non-coordinating BArF₂₄ anion, exhibit catalytic activity resulting from their ability to act as host for molecules bearing Lewis-acidic moieties. This host-guest behavior was evidenced by the binding of methanol within macrocycle **Te43**, as confirmed by ¹³C NMR titration, which revealed a binding constant of 2.66 M⁻¹ with a 1:1 association model. Compound **Te43** and other associated macrocycles could promote glycosylation reactions on *O*-protected, α-trichloroacetimidate-activated glycosyl donors. Reactions yields were variable depending on the macrocycle, but the β/α selectivity could be modulated depending on factors such as the concentration and bulkiness of the glycosyl acceptor. These findings suggest that glycosylation selectivity may result from competing coordination of either the glycosyl donor or acceptor within the macrocycle, thus favoring the formation of one diastereoisomer over the other depending on which reaction partner occupies the interior pocket of the catalyst.

Telluroxides have also been investigated for their potential application as transmembrane ion transporters. Langton and *coll.* explored the coordination chemistry of diaryltelluroxides in the search for multistate redox-switchable anion transporters based on the electrophilic character

<figure><img src="image_34.png" /><figcaption>**Fig. 28.** Redox-active telluroxide-based ion transmembrane transporter.</figcaption></figure>
<figure><img src="image_35.png" /><figcaption>Fig. 29. Coordination behavior of Te(CN)₄ (Te45) with diglyme (LB51).</figcaption></figure>

<figure><img src="image_36.png" /><figcaption>Fig. 30. ChB with hexavalent tellurium cation.</figcaption></figure>

of Te(IV) derivatives [151]. These species can reversibly switch to Te(II) or Te(VI) oxidation states, both of which are less efficient ChB donors, thereby enabling redox-controlled transport (Fig. 28). Telluroxides such as Te44 are able to bind to chloride anions through ChB, as demonstrated by ¹H NMR titration in the presence of TBACl. By this methodology, a binding constant of 935 M⁻¹ could be determined in deuterated acetonitrile with a 1:1 binding model. Anion transport experiments from unilamellar vesicles containing NaCl demonstrated that carrier Te44 successfully promoted anion transport, along with confirmation that both the telluride (Te (II)) and the tellurone (Te (VI)) have mediocre transport capacities. Addition of dithiothreitol (DTT) as a reducing agent was shown to halt the transport process by a reversible ON→OFF switch resulting from Te(IV) → Te(II) reduction. Inversely, the same ON→OFF process could be replicated upon the addition of cumene hydroperoxide, which readily oxidized Te(IV) to the inactive Te(VI) species. Such flexibility allows for more complex and unprecedented OFF→ON→OFF multistate switching upon successive reduction of the tellurium center, in a Te(VI) → Te(IV) → Te(II) sequence.

### 5.5. Other Te(IV) systems

Te(CN)₄ (Te45) was described to form both the mononuclear complex Te45/(LB51)₂ representing a rare case of a double coordination of a tellurium center with two diglyme ligands (LB51), and the coordination polymer Te45/LB51 (Fig. 29) [152]. In Te45/(LB51)₂, the Te(IV) center displays a seesaw-like structure similar to that of Te(IV) catecholates, diverging from the expected trigonal pyramidal structure. Moreover, the O—Te—CN angles deviate from the ideal linearity expected for a ChB, probably due to the steric demands imposed by two relatively bulky triether ligands. In the coordination polymer, the Te45/LB51 units are held together through Te···N interactions with angles slightly deviating from those expected for a ChB. In this case, however, the diglyme ligand seems to interact with Te through ChB as shown by a short distance of 2.621 Å and an angle of 158°.

## 6. ChB-based molecular complexes involving Te(VI) compounds

Hexavalent tellurium salts were found to behave as excellent ChB catalysts in different organic reactions [48]. In the solid state, the tellurium atom interacts through its σ-hole with the anion such as perchlorate ClO₄⁻ in tellurium salt Te46. In the case of the BaF₂₄ tellurium Te47, a molecule of water concomitantly interacts with the tellurium atom through ChB and with THF through hydrogen bonding (HB). This combination of ChB and HB was further proposed as the activation mode in tellurium-catalyzed glycosylation reactions (Fig. 30).

## 7. Conclusion

In this review, the ability of electrophilic tellurium to behave as a “coordination center” was highlighted by collecting examples from early and more recent literature. In most reported cases, the interaction between tellurium and the ligands (Lewis bases) was rationalized on the basis of the σ-hole concept. Indeed, the coordinating atom of the ligand typically approaches the tellurium center in a geometry corresponding to that of a chalcogen bond. Electrophilic species of tellurium at oxidation state 0, +2, +4 and +6 were shown to form ChB complexes with numerous ligands, in a similar way to metallic coordination complexes. This property was mainly demonstrated in the solid-state but recent studies involving highly electrophilic tellurium derivatives highlighted their potential for the formation of stable complexes also in solution. The fact that ChB emerges as a new mode of interaction in the coordination chemistry of electrophilic tellurium open new directions in the design and applications of tellurium complexes.

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Acknowledgement

The authors gratefully thank the University of Strasbourg and the Centre National de la Recherche Scientifique (CNRS) for their financial support. The Agence Nationale de la Recherche (ANR) is acknowledged for funding (ANR-21-07CE-0014). A. P. H. acknowledge the initiative of Excellence IDEX-Unistra (ANR-10-IDEX-0002-02) from the French national program “Investment for the Future” for a post-doctoral grant.

## Data availability

No data was used for the research described in the article.

## References

[1] T. Chivers, R.S. Laitinen, Tellurium: a maverick among the chalcogens, Chem. Soc. Rev. 44 (2015) 1725–1739, https://doi.org/10.1039/C4CS00434E.

[2] P. Pale, V. Mamane, Chalcogen bonding catalysis: tellurium, the last frontier? Chem. A Eur. J. 29 (2023) e202302755 https://doi.org/10.1002/chem.202302755.

[3] D. Jovanovic, M. Poliyodath Mohanan, S.M. Huber, Halogen, chalcogen, pnictogen, and tetrel bonding in non-covalent organocatalysis: an update, Angew. Chem. Int. Ed. 63 (2024) e202404823, https://doi.org/10.1002/anie.202404823.

[4] E.R.T. Tiekink, Te···N secondary-bonding interactions in tellurium crystals: supramolecular aggregation patterns and a comparison with their lighter congeners, Coord. Chem. Rev. 457 (2022) 214397, https://doi.org/10.1016/j.ccr.2021.214397.

[5] A. Dhaka, I.-R. Jeon, M. Fourmigué, Selective activation of chalcogen bonding: an efficient structuring tool toward crystal engineering strategies, Acc. Chem. Res. 57 (2024) 362–374, https://doi.org/10.1021/acs.accounts.3c00674.

[6] M.S. Taylor, Anion recognition based on halogen, chalcogen, pnictogen and tetrel bonding, Coord. Chem. Rev. 413 (2020) 213270, https://doi.org/10.1016/j.ccr.2020.213270.
[7] A. Singh, A. Torres-Huerta, F. Meyer, H. Valkenier, Anion transporters based on halogen, chalcogen, and pnictide bonds: towards biological applications. Chem. Sci. 15 (2024) 15006–15022, https://doi.org/10.1039/D4SC04644G.

[8] K.T. Mahmudov, A.V. Gurbanov, V.A. Aliyeva, M.F.C. Guedes da Silva, G. Resnati, A.J.L. Pombeiro, Chalcogen bonding in coordination chemistry. Coord. Chem. Rev. 464 (2022) 214556, https://doi.org/10.1016/j.ccr.2022.214556.

[9] K.J.R. Rosman, P.D.P. Taylor, Isotopic compositions of the elements 1997 (Technical report), Pure Appl. Chem. 70 (1998) 217–235, https://doi.org/10.1351/pac199870010217.

[10] J. Ibers, Tellurium in a twist. Nat. Chem. 1 (2009) 508, https://doi.org/10.1038/nchem.350.

[11] N. Belzile, Y.-W. Chen, Tellurium in the environment: a critical review focused on natural waters, soils, sediments and airborne particles. J. Appl. Geochem. 63 (2015) 83–92, https://doi.org/10.1016/j.apgeochem.2015.07.002.

[12] D.C. Dittmer, Tellurium, Chem. Eng. News Archive 81 (2003) 128, https://doi.org/10.1021/cen-v081n036.p128.

[13] R.C. Brasted, Tellurium. Encyclopedia Britannica. https://www.britannica.com/science/tellurium. (Accessed 15 September 2025).

[14] J. Zhang, W. Hu, Y. Li, A. Savoy, J. Sun, T.Y. Chi, Y. Wang, Advances in the catalytic production of acrylonitrile, Chem Catalysis 4 (2024) 100825, https://doi.org/10.1016/j.cheat.2023.100825.

[15] H. Chung, S. Friedrich, J. Becker, B. Friedrich, Purification principles and methodologies to produce high-purity tellurium, Can. Metal. Q. 63 (2024) 1626–1642, https://doi.org/10.1080/00084433.2024.2355031.

[16] K. Zweibel, The impact of tellurium supply on cadmium telluride photovoltaics, Science 328 (2010) 699–701, https://doi.org/10.1126/science.1189690.

[17] A. Romeo, E. Artegiani, CdTe-based thin film solar cells: past, present and future, Energies 14 (2021) 1684, https://doi.org/10.1016/j.energ.2021.01.061684.

[18] I.T. Witting, T.C. Chasapis, F. Ricci, M. Peters, N.A. Heinz, G. Hautier, G. J. Snyder, The thermoelectric properties of bismuth telluride, Adv. Elect. Mater. 5 (2019) 1800904, https://doi.org/10.1002/aem.201800904.

[19] U.S. Geological Survey Releases 2022 List of Critical Minerals. https://www.usgs.gov/news/national-news-release/us-geological-survey-releases-2022-list-critical-minerals, 2022 (accessed 18 September 2025).

[20] Solutions for Critical Raw materials-a European Expert Network- Tellurium factsheet 2023. https://screen.eu/crms-2023/, 2023 (accessed 18 September 2025).

[21] U.S. Geological Survey. Mineral commodity summaries 2025. https://pubs.usgs.gov/publication/mcs2025, 2025 (accessed 20 September 2025).

[22] F. Wöhler, Ueber neue Verbindungen des Telluräthyls, Justus Liebigs Ann. Chem. 84 (1852) 69–81, https://doi.org/10.1002/jlac.201804016.

[23] L.A. Ba, M. Döring, V. Jamier, C. Jacob, Tellurium: an element with great biological potency and potential, Org. Biomol. Chem. 8 (2010) 4203, https://doi.org/10.1039/c00b00086h.

[24] S. Yamago, Y. Ukai, A. Matsumoto, Y. Nakamura, Organotellurium-mediated controlled/living radical polymerization initiated by direct C–Te bond photolysis, J. Am. Chem. Soc. 131 (2009) 2100–2101, https://doi.org/10.1021/ja809689.

[25] P.R.O. Campos, G.P.P.P. Silva, Y. Shibuya, S. Koguchi, E.E. Alberto, Oxidation reactions promoted or catalyzed by organotellurium compounds, ACS Omega 10 (2025) 28691–28708, https://doi.org/10.1021/acsomega.5c03157.

[26] S. Singh, N. Yadav, S. Mahala, J. Yadav, K. Behera, G.K. Rao, H. Joshi, K. N. Sharma, Metal complexes featuring organotellurium ligands: synthesis, coordination behavior, and applications, Dalton Trans. 54 (2025) 7970–8014, https://doi.org/10.1039/D4DT05021.

[27] V.K. Jain, R.S. Chauhan, New vistas in the chemistry of platinum group metals with tellurium ligands. Coord. Chem. Rev. 306 (2016) 270–301, https://doi.org/10.1016/j.ccr.2015.07.009.

[28] A. Arora, P. Oswal, A. Datta, A. Kumar, Complexes of metals with organotellurium compounds and nanosized metal tellurides for catalysis, electrocatalysis and photocatalysis, Coord. Chem. Rev. 459 (2022) 214406, https://doi.org/10.1016/j.ccr.2022.214406.

[29] P.J. Dyson, A.F. Hill, A.G. Hulkes, A.J.P. White, D.J. Williams, Tetravalent tellurium ligands, Angew. Chem. Int. Ed. 38 (1999) 512–514, https://doi.org/10.1002/(SICI)1521-3773(19990215)38:4<512>:AID-ANIE512>3.0.CO;2-R.

[30] R.S. Chauhan, G. Kedarnath, A. Wadawale, A.M.Z. Slawin, V.K. Jain, Reactivity of 2-chalcogenopyridines with palladium-phosphine complexes: isolation of different complexes depending on the nature of chalcogen atom and phosphine ligand, Dalton Trans. 42 (2013) 259–269, https://doi.org/10.1039/C2DT30535F.

[31] M.C. Janzen, M.C. Jennings, R.J. Puddephatt, Oxidative addition of $Ph_2TeCl_2$ to a dimethylplatinum(II) complex: effects of secondary bonding in the platinum–tellurium products, Inorg. Chem. 42 (2003) 4553–4558, https://doi.org/10.1021/ic030057x.

[32] N.W. Alcock, Secondary bonding to nonmetallic elements, Adv. Inorg. Chem. Radiochem. 15 (1972) 1–58, https://doi.org/10.1016/S0065-2792(08)60016-3.

[33] R.E. Jr, R. Rosenfield, J.D. Dunitz Parthasarathy, Directional preferences of nonbonded atomic contacts with divalent sulfur. 1. Electrophiles and nucleophiles, J. Am. Chem. Soc. 99 (1977) 4860–4862. https://pubs.acs.org/doi/10.1021/ja00456a072.

[34] D.B. Werz, R. Gleiter, F. Rominger, Nanotube formation favored by chalcogen-chalcogen interactions, J. Am. Chem. Soc. 124 (2002) 10638–10639, https://doi.org/10.1021/ja027146d.

[35] D.B. Werz, T.H. Staeb, C. Benisch, B.J. Rausch, F. Rominger, R. Gleiter, Self-organization of chalcogen-containing cyclic alkynes and alkenes to yield

columnar structures. Org. Lett. 4 (2002) 339–342, https://doi.org/10.1021/ol016953z.

[36] S. Kolb, G.A. Oliver, D.B. Werz, Chemistry evolves, terms evolve, but phenomena do not evolve: from chalcogen–chalcogen interactions to chalcogen bonding, Angew. Chem. Int. Ed. 59 (2020) 22306–22310, https://doi.org/10.1002/anie.202007314.

[37] C.B. Aakeroy, D.L. Bryce, G.R. Desiraju, A. Frontera, A.C. Legon, F. Nicotra, K. Rissanen, S. Scheiner, G. Terraneo, P. Metrangolo, G. Resnati, Definition of the chalcogen bond (IUPAC Recommendations 2019), Pure Appl. Chem. 91 (2019) 1889–1892. doi: https://doi.org/10.1515/pac-2018-0713.

[38] A. Pizzi, G. Terraneo, C. Lo Iacono, R. Beccaria, A. Dhaka, G. Resnati, Taxonomy of chemical bondings: opportunities and challenges, Angew. Chem. Int. Ed. 64 (2025) e202506525, https://doi.org/10.1002/anie.202506525.

[39] R. Taylor, Correspondence on "taxonomy of chemical bondings: opportunities and challenges", Angew. Chem. Int. Ed. 64 (2025) e202517813 https://doi.org/10.1002/anie.202517813.

[40] R. Gleiter, G. Haberhauer, D.B. Werz, F. Rominger, C. Bleiholder, From noncovalent chalcogen–chalcogen interactions to supramolecular aggregates: experiments and calculations, Chem. Rev. 118 (2018) 2010–2041, https://doi.org/10.1021/acs.chemrev.7b00449.

[41] D.J. Pascoe, K.B. Ling, S.L. Cockroft, The origin of chalcogen-bonding interactions, J. Am. Chem. Soc. 139 (2017) 15160–15167, https://doi.org/10.1021/jacs.7b08511.

[42] T. Clark, M. Hennemann, J.S. Murray, P. Politzer, Halogen bonding: the σ-hole, J. Mol. Model. 13 (2007) 291–296, https://doi.org/10.1007/s00894-006-0130-2.

[43] J.S. Murray, P. Lane, T. Clark, P. Politzer, σ-Hole bonding: molecules containing group VI atoms, J. Mol. Model. 13 (2007) 1033–1038, https://doi.org/10.1007/s00894-007-0225-4.

[44] P. Politzer, J.S. Murray, Electrostatics and polarization in σ- and π-hole noncovalent interactions: an overview, ChemPhysChem 21 (2020) 579–588, https://doi.org/10.1002/cphc.201900968.

[45] F. De Vleeschouwer, M. Denayer, B. Pinter, P. Geerlings, F. De Proft, Characterization of chalcogen bonding interactions via an in-depth conceptual quantum chemical analysis, J. Comput. Chem. 39 (2018) 557–572, https://doi.org/10.1002/jcc.25099.

[46] C. Bleiholder, D.B. Werz, H. Köppel, R. Gleiter, Theoretical investigations on chalcogen-chalcogen interactions: what makes these nonbonded interactions bonding? J. Am. Chem. Soc. 128 (2006) 2666–2674, https://doi.org/10.1021/ja056827g.

[47] C. Bleiholder, R. Gleiter, D.B. Werz, H. Köppel, Theoretical investigations on heteronuclear chalcogen–chalcogen interactions: on the nature of weak bonds between chalcogen centers, Inorg. Chem. 46 (2009) 2249–2260, https://doi.org/10.1021/ic062110y.

[48] X. Li, Y. Liu, W. Wang, Y. Wang, A hexavalent tellurium-based chalcogen bonding catalysis platform: high catalytic activity and controlling of selectivity, J. Am. Chem. Soc. 147 (2025) 3233–3242, https://doi.org/10.1021/jacs.4c13004.

[49] P. Pale, V. Mamane, Chalcogen bonds: how to characterize them in solution? ChemPhysChem 24 (2023) e202200481.

[50] F. Zheng, Q. Huang, J. Xiang, Z. Zhu, J. Lu, J. Xu, Z. Liang, L. Xie, F. Song, Q. Sun, Constructing molecular networks on metal surfaces through tellurium-based chalcogen-organic interaction, ACS Nano 18 (2024) 28425–28432. https://pubs.acs.org/doi/10.1021/acsnano.4c11344.

[51] M. Ibrahim, W. Hassan, D.F. Meinerz, M. dos Santos, C.V. Klimaczewski, A. M. Deobald, M.S. Costa, C.W. Nogueira, N.B.V. Barbosa, J.B.T. Rocha, Antioxidant properties of diorganoyl diselenides and ditellurides: modulation by organic aryl or naphthyl moiety, Mol. Cell. Biochem. 371 (2012) 97–104, https://doi.org/10.1007/s11010-012-1426-4.

[52] A. Triphati, A. Daolio, A. Pizzi, Z. Guo, D.R. Turner, A. Baggioli, A. Famulari, G. B. Deacon, G. Resnati, H.B. Singh, Chalcogen bonds in selenocysteine seleninic acid, a functional GPx constituent, and in other seleninic or sulfinic acid derivatives, Chem. Asian J. 16 (2021) 2351–2360, https://doi.org/10.1002/asia.202100545.

[53] R. Weiss, E. Aubert, L. Groslambert, P. Pale, V. Mamane, Chalcogen bonding with diaryl ditellurides: evidence from solid state and solution studies, Chem. A Eur. J. 28 (2022) e202200395, https://doi.org/10.1002/chem.202200395.

[54] A. Tripathi, M. Calabrese, A. Pizzi, A. Dhaka, N. Demitri, D.R. Turner, G. B. Deacon, A. Frontera, G. Resnati, H.B. Singh, The role of chalcogen bonding in organic dichalcogenides of biological interest, Chem. Asian J. 20 (2025) e202401846, https://doi.org/10.1002/asia.202401846.

[55] J. Beckmann, S. Heitz, M. Hesse, Four distinctively different decomposition pathways of metastable supermesityltellurium(IV) trichloride, Inorg. Chem. 46 (2007) 3275–3282. https://doi.org/10.1021/ic062469m.

[56] J. Barluenga, F. Gonzalez-Bobes, M.C. Murguia, S.R. Ananthoju, J.M. Gonzalez, Bis(pyridine)iodonium tetrafluoroborate (IPy2BF4): a versatile oxidizing reagent, Chem. A Eur. J. 10 (2004) 4206–4213, https://doi.org/10.1002/chem.200400136.

[57] P.D. Boyle, W.I. Cross, S.M. Godfrey, C.A. McAuliffe, R.G. Pritchard, S. Sarwar, J. M. Sheffield, Synthesis and characterization of $Ph_4Te_4I$, containing a $Te_4$ square, and $Ph_3PTE(Ph)I$, Angew. Chem. Int. Ed. 39 (2000) 1796–1798, https://doi.org/10.1002/(SICI)1521-3773(20000515)39:10-1796::AID-ANIE1796>3.0.CO;2-G.

[58] J. Beckmann, J. Bolsinger, A. Duthie, P. Finke, E. Lork, C. Lüdtke, O. Mallow, S. Mebs, Mesityltellurenyl cations stabilized by triphenylpictogens [MesTe (EPh3)]⁺ (E = P, as, Sb), Inorg. Chem. 51 (2012) 12395–12406, https://doi.org/10.1021/ic3017722.
[59] S. Yadav, S. Raju, H.B. Singh, R.J. Butcher, Selone-stabilized aryltellurenyl cations, Dalton Trans. 45 (2016) 8458–8467, https://doi.org/10.1039/C6DT01081D.

[60] M.C. Aragoni, M. Arca, A.J. Blake, E. Cadoni, L.O. Copolovici, F. Isaia, V. Lippolis, S. Murgia, A.M. Pop, C. Silvestru, J.P. Tidey, R.A. Varga, Reaction of imidazoline-2-selene derivatives with mesityltellurenyl iodide: a unique example of a 3c-4e Se→Te→Se three-body system embedding a telluride cation, New J. Chem. 43 (2019) 11821–11831, https://doi.org/10.1039/C9NJ01593K.

[61] C.G. Hrib, P.G. Jones, W.-W. du Mont, V. Lippolis, F.A. Devillanova, Complexes of bidentate phosphane selenide ligands with mesityletellurenyl iodide and with tellurium diiodide, Eur. J. Inorg. Chem. 2006 (2006) 1294–1302, https://doi.org/10.1002/ejc.200500843.

[62] J. Jeske, W.-W. du Mont, P.G. Jones, Synthesis of a triiodide-like pentamesityltellurium cation by addition of dimesityltelluride to the remarkably electrophilic trimesitylditelluronium ion, Angew. Chem. Int. Ed. 36 (1997) 2219–2221, https://doi.org/10.1002/anie.19972219.

[63] J. Beckmann, P. Finke, S. Heitz, M. Hesse, Aryltellurenyl cation [RTE( Cr' 2)] + stabilized by an N-heterocyclic carbene, Eur. J. Inorg. Chem. 2008 (2008) 1921–1925, https://doi.org/10.1002/ejc.200800038.

[64] G. Resnati, D.L. Bryce, G.R. Desiraui, A. Frontera, I. Krossing, A.C. Legon, P. Metrangolo, F. Nicotra, K. Rissanen, S. Scheiner, G. Terraneo, Definition of the pnictogen bond (IUPAC Recommendations 2023), Pure Appl. Chem. 96 (2024) 135–145. doi: https://doi.org/10.1515/pac-2020-1002.

[65] D.J. Williams, V.L.H. Bevilacqua, P.A. Morson, W.T. Pennington, G.L. Schimek, N. T. Kawai, Main group metal halide complexes with sterically hindered thioethanes. Part XVII. The crystal and molecular structures of two new tellurium chloride complexes with 1,3-dimethyl-2(3H)-imidazolethione, Inorg. Chim. Acta 308 (2000) 129–134, https://doi.org/10.1016/S0020-1693(00)00234-6.

[66] G. Reeske, A.H. Cowley, Direct reactions of tellurium tetrahalides with chelating nitrogen ligands. Trapping of TeI₂ by a 1,2-bis(arylimino)acenaphthene (arylBIAN) ligand and C–H activation of an α,α'-diiminopyridine (DIMPY) ligand, Chem. Commun. 2006 (2006) 4856–4858, https://doi.org/10.1039/b610491F.

[67] J.L. Dutton, H.M. Tuononen, P.J. Ragogna, Tellurium(II)-centered dications from the pseudohalide "Te(OTf)₂", Angew. Chem. Int. Ed. 48 (2009) 4409–4413, https://doi.org/10.1002/anie.200901495.

[68] J.L. Dutton, P.J. Ragogna, Dicationic tellurium analogues of the classic N-heterocyclic carbene, Chem. A Eur. J. 16 (2010) 12454–12461, https://doi.org/10.1002/chem.201001447.

[69] J.W. Dube, M.M. Hänninen, J.L. Dutton, H.M. Tuononen, P.J. Ragogna, Homoleptic pnictogen–chalcogen coordination complexes, Inorg. Chem. 51 (2012) 8897–8903, https://doi.org/10.1021/ic300892p.

[70] J.L. Dutton, G.J. Farrar, M.J. Sgro, T.L. Battista, P.J. Ragogna, Lewis base sequestered chalcogen dihalides: synthetic sources of ChX₂ (Ch=Se, Te; X=Cl, Br), Chem. A Eur. J. 15 (2009) 10263–10271, https://doi.org/10.1002/chem.200901000.

[71] Y.C. Tse, A. Docker, I. Marques, V. Félix, P.D. Beer, Amphoteric chalcogen-bonding and halogen-bonding rotaxanes for anion or cation recognition, Nat. Chem. 17 (2025) 373–381, https://doi.org/10.1038/s41557-025-01742-x.

[72] T. Bunchuay, A. Docker, U. Eiamprasert, P. Surawatanawong, A. Brown, P. D. Beer, Chalcogen bond mediated enhancement of cooperative ion-pair recognition, Angew. Chem. Int. Ed. 59 (2020) 12007–12012, https://doi.org/10.1002/anie.202001125.

[73] A. Docker, C.H. Guthrie, H. Kuhn, P.D. Beer, Modulating chalcogen bonding and halogen bonding sigma-hole donor atom potency and selectivity for halide anion recognition, Angew. Chem. Int. Ed. 60 (2021) 21973–21978, https://doi.org/10.1002/anie.202108519.

[74] A. Docker, I. Marques, H. Kuhn, Z. Zhang, V. Félix, P.D. Beer, Selective potassium chloride recognition, sensing, extraction, and transport using a chalcogen-bonding heteroditopic receptor, J. Am. Chem. Soc. 144 (2022) 14778–14789, https://doi.org/10.1021/jacs.2c05333.

[75] A. Docker, Y.C. Tse, H.M. Tay, Z. Zhang, P.D. Beer, Ammonium halide selective ion pair recognition and extraction with a chalcogen bonding heteroditopic receptor, Dalton Trans. 53 (2024) 11141–11146, https://doi.org/10.1039/d4dt01376.

[76] P. Wonner, T. Steinke, L. Vogel, S.M. Huber, Carbonyl activation by selenium- and tellurium-based chalcogen bonding in a Michael addition reaction, Chem. A Eur. J. 26 (2020) 1258, https://doi.org/10.1002/chem.201905057.

[77] T. Steinke, P. Wonner, R.M. Gauld, S. Heinrich, S.M. Huber, Catalytic activation of imines by chalcogen bond donors in a Povarov [4+2] cycloaddition reaction, Chem. A Eur. J. 28 (2022) e20220917, https://doi.org/10.1002/chem.20220917.

[78] H.-Y. Duan, S.-T. Han, T.-G. Zhan, L.-J. Liu, K.-D. Zhang, Visible-light-switchable tellurium-based chalcogen bonding: photocontrolled anion binding and anion abstraction catalysis, Angew. Chem. Int. Ed. 62 (2023) e202212707, https://doi.org/10.1002/anie.202212707.

[79] A.V. Rozhkov, E.A. Katlenok, M.V. Zhmykhova, A.Y. Ivanov, M.L. Kuznetsov, N. A. Bokach, V.Y. Kukushkin, Metal-involving chalcogen bond. The case of platinum(II) interaction with Se/Te-based σ-hole donors, J. Am. Chem. Soc. 143 (2021) 15701–15710, https://doi.org/10.1021/jacs.1n06498.

[80] A.A. Busygina, A.A. Eliseeva, A.V. Rozhkov, D.M. Ivanov, R.M. Gomila, A. Frontera, N.A. Bokach, V.Y. Kukushkin, Synergistic α/π-hole interactions directing supramolecular assembly: tellurium···platinum chalcogen bonding enhanced by π-stacking, Cryst. Growth Des. 24 (2024) 10235–10246, https://doi.org/10.1021/acs.cgi.4c01236.

[81] Y.V. Torubaev, A.V. Rozhkov, I.V. Skabitsky, R.M. Gomila, A. Frontera, V. Y. Kukushkin, Heterovalent chalcogen bonding: supramolecular assembly driven

by the occurrence of a tellurium(II)···Ch(I) (Ch = S, Se, Te) linkage, Inorg. Chem. Front. 9 (2022) 5635–5644, https://doi.org/10.1039/d2qi01420c.

[82] A. Dhaka, O. Jeannin, I.-R. Jeon, E. Aubert, E. Espinosa, M. Fourmigué, Activating chalcogen bonding (ChB) in alkylseleno/alkyltelлуroacetylenes toward chalcogen bonding directionality control, Angew. Chem. Int. Ed. 59 (2020) 23583–23587, https://doi.org/10.1002/anie.202011981.

[83] A. Dhaka, O. Jeannin, E. Aubert, E. Espinosa, M. Fourmigué, Supramolecular rectangles through directional chalcogen bonding, Chem. Commun. 57 (2021) 4560–4563, https://doi.org/10.1039/D1CC00789K.

[84] M. Beau, S. Lee, S. Kim, W.-S. Han, O. Jeannin, M. Fourmigué, E. Aubert, E. Espinosa, I.-R. Jeon, Strong σ-hole activation on icosahedral carbane derivatives for a directional halide recognition, Angew. Chem. Int. Ed. 60 (2021) 366–370, https://doi.org/10.1002/anie.20201462.

[85] G.E. Garrett, E.I. Carrera, D.S. Seferos, M.S. Taylor, Anion recognition by a bidentate chalcogen bond donor, Chem. Commun. 52 (2016) 9881–9884, https://doi.org/10.1039/C6CC04818H.

[86] E. Navarro-García, B. Galmés, M.D. Velasco, A. Frontera, A. Caballero, Anion recognition by neutral chalcogen bonding receptors: experimental and theoretical investigations, Chem. A Eur. J. 26 (2020) 4706–4713, https://doi.org/10.1002/chem.201905786.

[87] T. Chivers, X. Gao, M. Parvez, Preparation, crystal structures, and isomerization of the tellurium diimide dimers RNTE(µ-NR')₂TeNR (R = R' = 'Bu; R = PPh₂NiSiMe₃, R' = 'Bu, ⁴Oct): X-ray structure of the telluradiazole dimer [²[Bu₃C₆H₂N₂Te]₂], Inorg. Chem. 35 (1996) 9–15, https://doi.org/10.1021/ic950154t.

[88] A.F. Cozzolino, I. Vargas-Baca, S. Mansour, A.H. Mahmoudkhani, The nature of the supramolecular association of 1,2,5-chalcogenodiazoles, J. Am. Chem. Soc. 127 (2005) 3184–3190, https://doi.org/10.1021/ja044005y.

[89] P.C. Ho, P. Szydłowski, J. Sinclair, P.J.W. Elder, J. Kübel, C. Gendy, L.M. Lee, H. Jenkins, J.F. Britten, D.R. Morim, I. Vargas-Baca, Supramolecular macrocycles reversibly assembled by Te···O chalcogen bonding, Nat. Commun. 7 (2016) 11299, https://doi.org/10.1038/ncomms11299.

[90] A. Kremer, A. Fermi, N. Biot, J. Wouters, D. Bonifazi, Supramolecular wiring of benzo-1,3-chalcogenozoles through programmed chalcogen bonding interactions, Chem. A Eur. J. 22 (2016) 5665–5675, https://doi.org/10.1002/chem.201504328.

[91] L.-J. Riwar, N. Trapp, K. Root, R. Zenobi, F. Diederich, Supramolecular capsules: strong versus weak chalcogen bonding, Angew. Chem. Int. Ed. 57 (2018) 17259–17264, https://doi.org/10.1002/anie.201812095.

[92] S. Mehrparvar, C. Wölper, R. Gleiter, G. Haberhauer, The carbonyl···telлуrazole chalcogen bond as a molecular recognition unit: from model studies to supramolecular organic frameworks, Angew. Chem. Int. Ed. 59 (2020) 17154–17161, https://doi.org/10.1002/anie.202005374.

[93] A.F. Cozzolino, J.F. Britten, I. Vargas-Baca, The effect of steric hindrance on the association of telluradiazoles through Te-N secondary bonding interactions, Cryst. Growth Des. 6 (2006) 181–186, https://doi.org/10.1021/cg050260y.

[94] A.F. Cozzolino, P.S. Whitfield, I. Vargas-Baca, Supramolecular cycloprotoprotism of the crystalline phases of 4,5,6,7-tetrafluorobenzo-2,1,3-telluradiazole, J. Am. Chem. Soc. 132 (2010) 17265–17270, https://doi.org/10.1021/ja10202376.

[95] N.A. Semenov, N.A. Pushkarevsky, J. Beckmann, P. Finke, E. Lork, R. Mews, I. Y. Bagryanskaya, Y.V. Gatilov, S.N. Konchenko, V.G. Vasiliev, A.V. Zibarev, Tellurium–nitrogen x-heterocyclic chemistry – synthesis, structure, and reactivity toward halides and pyridine of 3,4-dicyano-1,2,5-telluradiazole, Eur. J. Inorg. Chem. 2012 (2012) 3693–3703, https://doi.org/10.1002/ejc.201200376.

[96] N.A. Semenov, A.V. Lonchakov, N.A. Pushkarevsky, E.A. Suturina, V.V. Korolev, E. Lork, V.G. Vasiliev, S.N. Konchenko, J. Beckmann, N.P. Gritsan, A.V. Zibarev, Coordination of halide and chalcogenolate anions to heavier 1,2,5-chalcogenodiazoles: experiment and theory, Organometallics 33 (2014) 4302–4314, https://doi.org/10.1021/om5006403.

[97] N.A. Semenov, D.E. Gorbunov, M.V. Shakhova, G.E. Salnikov, I.Y. Bagryanskaya, V.V. Korolev, J. Beckmann, N.P. Gritsan, A.V. Zibarev, Donor–acceptor complexes between 1,2,5-chalcogenodiazoles (Te, Se, S) and the pseudohalides CN⁻ and XCN⁻ (X=O, S, Se, Te), Chem. A Eur. J. 24 (2018) 12983–12991, https://doi.org/10.1002/chem.201802257.

[98] V. Kumar, Y. Xu, D.L. Bryce, Double chalcogen bonds: crystal engineering stratagems via diffraction and multinuclear solid-state magnetic resonance spectroscopy, Chem. A Eur. J. 26 (2020) 3275–3286, https://doi.org/10.1002/chem.201904795.

[99] Y. Xu, V. Kumar, M.J.Z. Bradshaw, D.L. Bryce, Chalcogen-bonded cocrystals of substituted pyridine N-oxides and chalcogenodiazoles: an X-ray diffraction and solid-state NMR investigation, Cryst. Growth Des. 20 (2020) 7910–7920, https://doi.org/10.1021/acs.cgi.0c01173.

[100] E.A. Chulanova, E.A. Radiush, I.K. Shundrina, I.Y. Bagryanskaya, N.A. Semenov, J. Beckmann, N.P. Gritsan, A.V. Zibarev, Lewis ambiphilicity of 1,2,5-chalcogenodiazoles for crystal engineering: complexes with crown ethers, Cryst. Growth Des. 20 (2020) 5868–5879, https://doi.org/10.1021/acs.cgi.0c00536.

[101] G.E. Garrett, G.L. Gibson, R.N. Straus, D.S. Seferos, M.S. Taylor, Chalcogen bonding in solution: interactions of benzotelluradiazoles with anionic and uncharged Lewis bases, J. Am. Chem. Soc. 137 (2015) 4126–4133, https://doi.org/10.1021/ja512183e.

[102] P.C. Ho, H.A. Jenkins, J.F. Britten, I. Vargas-Baca, Building new discrete supramolecular assemblies through the interaction of iso-tellurazole N-oxides with Lewis acids and bases, Faraday Discuss. 203 (2017) 187–199, https://doi.org/10.1039/C7FD00075H.
[103] G. Haberhauer, R. Gleiter, The nature of strong chalcogen bonds involving chalcogen-containing heterocycles, Angew. Chem. Int. Ed. 59 (2020) 21236-21243, https://doi.org/10.1002/anie.202010309.

[104] D.O. Cowan, M.D. Mays, T.J. Kistenmacher, T.O. Poehler, M.A. Beno, A.M. Kini, J. M. Williams, Y.-K. Kwok, K.D. Carlson, L. Xiao, J.J. Novoa, M.-H. Whangbo, Structural and electronic properties of TXF-TCNQ (X = S, Se, Te), Mol. Cryst. Liq. Cryst. 181 (1990) 43-58, https://doi.org/10.1080/0026894008035991.

[105] P.J. Antikainen, P.J. Mälkönen, Darstellung und thermogravimetrische Untersuchung einer neuen Tellur—Brenzcatechin-Verbindung, Z. Anorg. Allg. Chem. 299 (1959) 292-296, https://doi.org/10.1002/zaac.19592990506.

[106] O. Lindqvist, The crystal structure of tellurium(IV) catecholate, Te(C₆H₄O₂)₂, Acta Chem. Scand. 21 (1967) 1473-1483, https://doi.org/10.3891/acta.chem. scand.21-1473.

[107] J.M. Kieser, L.O. Jones, N.J. Lin, M. Zeller, G.C. Schatz, S.C. Bart, Synthesis and characterization of tellurium catecholates and their N-oxide adducts, Inorg. Chem. 60 (2021) 3460-3470, https://doi.org/10.1021/acs.inorgchem.1c00126.

[108] T.A. Annan, A. Ozarowski, Z. Tian, D.G. Tuck, The reaction of some substituted ortho-benzoquinones with elemental tellurium and with tellurium(II) compounds, J. Chem. Soc. Dalton Trans. 1992 (1992) 2931-2938. doi: https://doi.org/10.1 039/dt9920002931.

[109] E. Hough, D.G. Nicholson, A.K. Vasudevan, Stereochemical role of lone pairs in main-group elements. Part 3. Structure and bonding in trichloro(1,4,7,10,13- pentaoxacyclopentadecane)antimony(III) studied by means of X-ray crystallography at 120 K, J. Chem. Soc. Dalton Trans. 1987 (1987) 427-430, https://doi.org/10.1039/dt9870000427.

[110] P.A. Petrov, Adducts of sterically hindered tellurium catecholate with ethers, Russ. Coord. Chem. 49 (2023) 354-359, https://doi.org/10.31857/ s0132344X22600448.

[111] P.A. Petrov, E.A. Filippova, T.S. Sukhikh, A.S. Novikov, M.N. Sokolov, Sterically hindered tellurium(IV) catecholate as a Lewis acid, Inorg. Chem. 61 (2022) 9184-9194, https://doi.org/10.1021/acs.inorgchem.2c00751.

[112] P.A. Petrov, E.A. Filippova, T.S. Sukhikh, Adducts of sterically hindered tellurium catecholate with N-methylpyrrolidone, Russ. Coord. Chem. 50 (2024) 683-688, https://doi.org/10.1134/S1070328424600530.

[113] P.A. Petrov, E.A. Filippova, T.S. Sukhikh, D.G. Sheven, A.S. Novikov, Adducts of a sterically hindered tellurium(IV) catecholate with diimines, New J. Chem. 48 (2024) 15483-15492, https://doi.org/10.1039/D4NJ024692A.

[114] D.P. Stevenson, V. Schomaker, An electron diffraction investigation of the molecular structure of tellurium tetrachloride, J. Amer. Chem. Soc. 62 (1940) 1267-1270, https://doi.org/10.1021/ja01862a080.

[115] D.A. Couch, P.S. Elmes, J.E. Fergusson, M.L. Greenfield, C.J. Wilkins, Chemistry of selenium and tellurium tetrahaldides: ionization of the chlorides and bromides in solution and the constitution of their adducts, J. Chem. Soc. A 1967 (1967) 1813-1817, https://doi.org/10.1039/ji19670001813.

[116] C.J. Carmalt, N.C. Norman, L.J. Farrugia, Octahedral coordination complexes of tellurium tetrachloride, Polyhedron 14 (1995) 1405-1413, https://doi.org/ 10.1016/0277-5387(94)00417-D.

[117] W. Levason, G. Reid, M. Victor, W. Zhang, Tellurium(II) and tellurium(IV) complexes of phosphine chalcogenide ligands, Synthesis and X-ray structures, Polyhedron 28 (2009) 4010-4016, https://doi.org/10.1016/j.poly.2009.08.025.

[118] J. Novosad, K.W. Törnroos, M. Necas, A.M.Z. Slawin, J.D. Woollins, S. Husebye, Reaction of large-bite ligands with various tellurium compounds, Polyhedron 18 (1999) 2861-2867, https://doi.org/10.1016/S0277-5387(99)00195-3.

[119] M. Necas, J. Novosad, S. Husebye, Tellurium complexes with new, large-bite dithio ligands. The crystal structures of cis- and trans-[Te{Ph₂P(S)-N-P(S) (OPh₂)₂}] and [(4-MeOC₆H₄TeCl₃)₂(µ-Pr₂P(S)-F-Pc(S)IPr₂)], J. Organomet. Chem. 623 (2001) 124-130, https://doi.org/10.1016/j.organchem.2012.09.007.

[120] S.S. Dos Santos, B.N. Cabral, U. Abram, E.S. Lang, Bis(4-pyridyl)ditelluride as starting material for the synthesis of zwitterionic compounds and metal complexes, J. Organomet. Chem. 723 (2013) 115-121, https://doi.org/10.1016/ j.jorganchem.2012.09.007.

[121] E. Schulz Lang, G.A. Casagrande, G. Manzoni De Oliveira, G.N. Ledesma, S. S. Lemos, E.E. Castellano, U. Abram, One-pot synthesis and structure of organochalcogen halides with mixed valence states, Eur. J. Inorg. Chem. 2006 (2006) 958-964, https://doi.org/10.1002/ejic.200500803.

[122] R.M. Gomila, A. Frontera, E.R.T. Tiekink, Te···I secondary-bonding interactions in crystals containing tellurium(II), tellurium(IV) and iodide atoms: supramolecular aggregation patterns, nature of the non-covalent interactions and energy considerations, CrystEngComm 26 (2024) 2784-2795, https://doi.org/10.1039/ D4CE00305E.

[123] K.J. Wynne, P.S. Pearson, Chalcogen chemistry. V., Complexes of organochalcogen trihalides with tetramethylthiourie, Inorg. Chem. 10 (1971) 2735-2739, https:// doi.org/10.1021/ic50106a022.

[124] K.K. Verma, S. Chhabra, Studies on 1,10-phenanthroline complexes of some hydroxyaryltellurium trihalides, Phosphorus Sulfur Silicon Relat. Elem. 183 (2008) 3037-3045, https://doi.org/10.1080/10426500802059760.

[125] G.A. Casagrande, E. Schulz Lang, B. Tirloni, R.A. Burrow, G. Manzoni De Oliveira, S.S. Lemos, Synthesis and crystal structures of neutral complexes of tellurium(IV) [·[PhTeX₃L](X = Br, I, = ethylenethiourea), Z. Anorg. Allg. Chem. 632 (2006) 893-896, https://doi.org/10.1002/zaac.200600001].

[126] C. Gurnani, M. Jura, W. Levason, R. Ratnani, G. Reid, M. Webster, Preparation and structures of tellurium(IV) halide complexes with thioether coordination, Dalton Trans. 2009 (2009) 4122, https://doi.org/10.1039/b902771h.

[127] K.K. Verma, K.K. Reena, Complexes of 4-hydroxyphenyltellurium trihalides with piperidine, dimethylformamide and thiourea, Synth. React. Inorg. Met. Org. Chem. 29 (1999) 499-512, https://doi.org/10.1080/00945719909349465.

[128] K.K. Verma, Reena, studies on thiourea complexes of some hydroxyaryltellurium trichlorides, Phosphorus Sulfur Silicon Relat. Elem. 148 (1999) 227-234, https:// doi.org/10.1080/104265099080307103.

[129] K.K. Verma, R. Dahiya, Synthesis and characterization of pyridine and bipyridine complexes of 4-hydroxyphenyltellurium trihalides, Synth. React. Inorg. Met. Chem. 29 (1999) 1299-1314, https://doi.org/10.1080/00945719909349529.

[130] K.K. Verma, R. Dahiya, D. Soni, Synthesis and characterization of complexes of some hydroxyaryltellurium trichlorides with N-donor ligands, Synth. React. Inorg. Met. Org. Chem. 29 (1999) 1033-1052, https://doi.org/10.1080/ 00945719909349509.

[131] J.L. Dutton, A. Sutrisno, R.W. Schurko, P.J. Ragoyna, Synthesis and characterization of cationic selenium-nitrogen heterocycles from tert-butyl-DAB (DAB = 1,4-di-tert-butyl-1,3-diazabutadiene) and SeX₄ via the reductive elimination of X₂ (X = Cl, Br): a distinct contrast with tellurium, Dalton Trans. 2008 (2008) 3470-3477, https://doi.org/10.1039/b719779a.

[132] H. Liu, Z. Han, Y. Lu, Z. Xu, W. Zhu, Cation-anion chalcogen bonds in ion pairs: a combined crystallographic survey and computational investigation, Comput. Theor. Chem. 1242 (2024) 114985, https://doi.org/10.1016/j. comptc.2024.114985.

[133] M.J. Collins, J.A. Ripmeester, J.F. Sawyer, Tellurium-125 solid-state NMR spectra and secondary bonding arrangements for some salts of the trimethyltellurium and triphenyltellurium cations, J. Am. Chem. Soc. 110 (1988) 8583-8590, https://doi.org/10.1021/ja00234a002.

[134] T.M. Klapötke, B. Krumm, P. Mayer, H. Piotrowski, I. Schwab, M. Vogt, Synthesis and structures of triorganotellurium pseudohalides, Eur. J. Inorg. Chem. 2002 (2002) 2701-2709, https://doi.org/10.1002/1099-0682(200210)2002:10<2701::AID-EJIC2701>3.0.CO;2-G.

[135] Y. Zhou, Q. Zhang, S. Jia, H. Ye, L. You, Neighboring chalcogen bonding for controlling dynamic imine chemistry in aqueous media, Org. Lett. 27 (2025) 2438-2443, https://doi.org/10.1021/acs.orglett.5c00359.

[136] N.V. Kirij, Y.L. Yagupolskii, W. Tyrra, I. Pantenburg, D. Naumann, The structure of tris(trifluoromethyl)tellurium fluoride dimethylformamide, [Te(CF₃)₃DMF (µ-F)]ₐ, Z. Anorg. Allg. Chem. 633 (2007) 943-945, https://doi.org/10.1002/ zaac.2007000038.

[137] F. Hu, C. Xu, H.-T. Shi, Q. Chen, Q.-F. Zhang, µ-(acetic acid)-di-µ-chlorido-bis [triphenyltellurium(IV)] monohydrate, Acta Crystallogr. Sect. E 69 (2013) o1171, https://doi.org/10.1107/S160053681301739X.

[138] H. Zhao, F.P. Gabbai, A bidentate Lewis acid with a tellurium ion as an anion- binding site, Nat. Chem. 2 (2010) 984-990, https://doi.org/10.1038/nchem.838.

[139] R. Weiss, E. Aubert, L. Groslambert, P. Pale, V. Mamane, Evidence for and evaluation of fluorine-tellurium chalcogen bonding, Chem. Sci. 14 (2023) 7221-7229, https://doi.org/10.1039/D3SC00849E.

[140] T.-P. Lin, F.P. Gabbai, Two-electron redox chemistry at the dinuclear core of a tept platform: chlorine photoreactive elimination and isolation of a TeVtPd complex, J. Am. Chem. Soc. 134 (2012) 12230-12238, https://doi.org/10.1021/ ja3046074.

[141] T. Lin, F.P. Gabbai, Telluronium ions as σ-acceptor ligands, Angew. Chem. Int. Ed. 52 (2013) 3864-3868, https://doi.org/10.1002/anie.201300337.

[142] B. Zhou, F.P. Gabbai, Redox-controlled chalcogen-bonding at tellurium: impact on Lewis acidity and chloride anion transport properties, Chem. Sci. 11 (2020) 7495-7500, https://doi.org/10.1039/D5SC02872J.

[143] B. Zhou, F.P. Gabbai, Anion chelation via double chalcogen bonding: the case of a bis-tellurium dication and its application in electrophilic catalysis via metal-chloride bond activation, J. Am. Chem. Soc. 143 (2021) 8625-8630, https://doi.org/10.1021/jacs.1c04482.

[144] R. Weiss, E. Aubert, P. Pale, V. Mamane, Chalcogen-bonding catalysis with tellurium cations, Angew. Chem. Int. Ed. 60 (2021) 19281-19286, https://doi. org/10.1002/anie.202105482.

[145] L. Groslambert, Y. Cornaton, M. Ditte, E. Aubert, P. Pale, A. Tkatchenko, J. Djkic, V. Mamane, Affinity of tellurium chalcogen bond donors for Lewis bases in solution: a critical experimental-theoretical joint study, Chem. A Eur. J. 30 (2024) e202302933, https://doi.org/10.1002/chem.202302933.

[146] L. Groslambert, A. Padilla-Hernandez, R. Weiss, P. Pale, V. Mamane, Chalcogen- bond catalysis: tellurium-catalyzed [4+2]-cyclocondensation of (in situ generated) aryl imines with alkenes, Chem. A Eur. J. 29 (2023) e202203372, https://doi.org/10.1002/chem.202203372.

[147] L. Groslambert, P. Pale, V. Mamane, Tellurium-catalyzed halogenation reactions: chalcogen-bond activation of N-halosuccinimides and catalysis, Chem. A Eur. J. 30 (2024) e202401650, https://doi.org/10.1002/chem.202401650.

[148] L. Groslambert, Y. Cornaton, P. Pale, M. Ditte, A. Tkatchenko, J.-P. Djkic, V. Mamane, Chalcogen bonding with tellurium cations: toward selective population of tellurium σ-holes by Lewis bases, J. Org. Chem. 90 (2025) 8254-8268, https://doi.org/10.1021/acs.joc.5c00744.

[149] A. Docker, A.J. Martínez Martínez, H. Kuhn, P.D. Beer, Organotelluroxane molecular clusters assembled via Te···X (X = Cl, —, Br) chalcogen bonding anion template interactions, Chem. Commun. 58 (2022) 3318-3321, https://doi. org/10.1039/D2CC00320A.

[150] W. Wang, B. Yu, Y.-C. Gu, Y. Wang, A macrocyclic chalcogen bonding catalysis system, Org. Chem. Front. 12 (2025) 2970-2977, https://doi.org/10.1039/ D5Q000101C.

[151] A. Docker, T.G. Johnson, H. Kuhn, Z. Zhang, M.J. Langton, Multistate redox- switchable ion transport using chalcogen-bonding anionophores, J. Am. Chem. Soc. 145 (2023) 2661-2668, https://doi.org/10.1021/jacs.2c12892.

[152] D. Lentz, M. Szwak, [Te(CN)₄] versus [Te(CN)₃(µ-CN)₃], Dalton Trans. 2008 (2008) 1289-1291, https://doi.org/10.1039/b714869k.