Authors: Dmitry I. Nazarov | Jorge Labella | Alexey V. Kuźmin | Maxim A. Faraonov | Evgenii N. Ivanov | Salavat S. Khasanov | Tomás Torres⊗ | Mikhail K. Islyaikin | Dmitri V. Konarev
Source: CCS Chemistry (article, 2024-03-05)
Field: Materials Science — Materials Chemistry

Expanded Porphyrin Exhibiting Off-Centered Out-of-Plane Coordination to Dysprosium Open AccessCCS ChemistryRESEARCH ARTICLES28 Mar 2024Expanded Porphyrin Exhibiting Off-Centered Out-of-Plane Coordination to Dysprosium Dmitry I. Nazarov, Jorge Labella, Alexey V. Kuzmin, Maxim A. Faraonov, Evgenii N. Ivanov, Salavat S. Khasanov, Tomas Torres, Mikhail K. Islyaikin and Dmitri V. Konarev Dmitry I. Nazarov Federal Research Center of Problems of Chemical Physics and Medicinal Chemistry RAS, 142432 Chernogolovka , Jorge Labella Department of Organic Chemistry, Universidad Autónoma de Madrid, 28049 Madrid , Alexey V. Kuzmin Institute of Solid-State Physics RAS, 142432 Chernogolovka , Maxim A. Faraonov Federal Research Center of Problems of Chemical Physics and Medicinal Chemistry RAS, 142432 Chernogolovka , Evgenii N. Ivanov Research Institute of Macroheterocycles, Ivanovo State University of Chemistry and Technology, 15300 Ivanovo G. A. Krestov Institute of Solution Chemistry of the Russian Academy of Sciences, 153045 Ivanovo , Salavat S. Khasanov Institute of Solid-State Physics RAS, 142432 Chernogolovka , Tomas Torres *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Department of Organic Chemistry, Universidad Autónoma de Madrid, 28049 Madrid Institute for Advanced Research in Chemical Sciences, Universidad Autónoma de Madrid, 28049 Madrid IMDEA-Nanociencia, 28049 Madrid , Mikhail K. Islyaikin *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Research Institute of Macroheterocycles, Ivanovo State University of Chemistry and Technology, 15300 Ivanovo G. A. Krestov Institute of Solution Chemistry of the Russian Academy of Sciences, 153045 Ivanovo and Dmitri V. Konarev *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Federal Research Center of Problems of Chemical Physics and Medicinal Chemistry RAS, 142432 Chernogolovka https://doi.org/10.31635/ccschem.024.202303824 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail The complexation of high-spin lanthanides to porphyrinoids is a powerful strategy for the development of advanced molecular magnets. In this context, the use of expanded porphyrinoids remains elusive since their coordination chemistry is challenging to control. Herein, taking inspiration from on-surface chemistry, we explored the coordination of Dy3+ to a six-membered porphyrinoid, namely, the hemihexaphyrazine H3Hhp. Remarkably, we observed the selective formation of a mono-nuclear off-centered, out-of-plane H2Hhp-Dy3+ complex when performing the complexation under reductive conditions. During this reaction, the oxidation state of the macrocycle did not change. Employing X-ray diffraction analysis, we found that the coordination number of Dy in this complex was 8. The macrocycle cocrystallized with decamethylcobaltocene (Cp2*Co) molecules, giving rise to a well-ordered solid-state packing, governed by π–π interactions. As a result of this organization, a small magnetic coupling between the neighboring molecules was observed. All in all, this work provides key insights into the coordination of magnetically active metals with expanded porphyrinoids, thus motivating the development of advanced spintronic devices. Download figure Download PowerPoint Introduction Single molecule magnetism offers attractive routes toward engineering advanced spintronic devices.1 High-performing single molecule magnets (SMMs) can be readily obtained by complexing paramagnetic metal centers into π-conjugated macrocycles.2 In this context, lanthanide3+ porphyrinoids have been extensively investigated by virtue of their multiple advantages such as high blocking temperatures and ultrahard magnetic behaviors.3–6 Due to their robust tetradentate character, porphyrins (Ps) and phthalocyanines (Pcs) have dominated this field, leading to the development of numerous SMMs with varying sizes, shapes, and supramolecular arrangements in which the magnetic response and spin–orbit coupling can be fine-tuned simply by changing the metallated Ln3+ cation.7–9 Nevertheless, the exploration of SMMs based on porphyrinoids presenting more than four coordination points would open the door to exotic structures, leading to unconventional magnetic responses. Expanded porphyrinoids are analogs of Ps and Pcs featuring larger cores.10–12 These derivatives are known for exhibiting a rich, but at the same time complex, coordination chemistry, whereby multiple metals can be accommodated in their inner cavities, separately or even simultaneously.7,13 By presenting five, six, or more coordinating atoms, expanded porphyrinoids can efficiently satisfy the tendency of earth-rare metals to present high-coordination numbers. Examples include texaphyrins, which have proven to be useful ligands for lanthanides (e.g., Gd, Ce, Pr, Nd, Sm, Eu, and more)14 or dipyriamethyrins, which can stabilize several actinoid metals such as Th, U, and Np.15 However, despite their envisioned potential, the coordination of magnetically active metals with expanded Ps focused on developing SMMs remains elusive. This is primarily ascribed to the fact that very little is still known about the coordination chemistry of these compounds with Ln3+ metals. Thus, establishing fundamental insights in that direction is a crucial step for the development of expanded Ps in molecular magnetism. On a metallic surface, the dimensionality of a given reaction is reduced from three to two.16,17 In principle, this would simplify the outcome of a given reaction, at least from a structural standpoint. Based on this premise, we envisioned that on-surface chemistry could be employed to provide initial insights into reactions with high complexity, which could then be extrapolated to in-solution methodologies. Keeping this idea in mind, in 2017, some of us explored the on-surface coordination of Dy,18 a metal widely used in the preparation of SMMs, with an expanded porphyrin, namely 2,3,5,10,12,13,15,20,22,23,25,30-dodecaazahexaphyrin (H3Hhp) (Figure 1b).19–22 In this work, a H3Hhp monolayer was formed on Au (111), and subsequently exposed to a flux of dysprosium atoms. Remarkably, efficient macrocycle metalation was observed after annealing, leading to an unusual off-centered Dy-H3Hhp coordination complex. Figure 1 | (a) Reported four-membered porphyrinoid-Dy3+ complexes (top) and on-surface synthesized Dy-H3Hhp complex. (b) Off-centered out-of-plane Dy-H3Hhp complex synthesized in solution in this work. Download figure Download PowerPoint Hereby, inspired by the intriguing results observed on metallic surfaces, we explored the formation of Dy-H3Hhp complexes in solution. Remarkably, we observed that the reaction of H3Hhp with Dy3+ precursor led to the formation of 1, a mononuclear Dy-H2Hhp complex wherein the Dy atom exhibited an off-centered out-of-plane coordination to the porphyrinoid, similar to previous on-surface observation. We then evaluated the impact of Dy coordination on the electronic and structural properties of the H3Hhp macrocycle both experimentally and theoretically. Interestingly, binuclear complexes were not found, despite using up to three equivalents of the Dy source. The origin of this finding was unveiled through theoretical calculations. It should be noted that a typical approach involved exploring a reaction in a solution before applying it to the on-surface methods. Therefore, this work serves as a paradigmatic example of how on-surface chemistry can inspire solution chemistry. Experimental Methods Instrumentation and materials UV–visible–near-infrared (NIR) spectra were measured in KBr pellets with a PerkinElmer Lambda 1050 spectrometer (PerkinElmer, USA) in the 250–2500 nm range. Fourier transform infrared (FT-IR) spectra were obtained in KBr pellets with a PerkinElmer Spectrum 400 spectrometer (400–7800 cm−1; PerkinElmer, USA). Electron paramagnetic resonance (EPR) spectra were recorded for a polycrystalline sample of 1 from room temperature (RT) down to liquid helium temperature with a JEOL JES-TE 200 X-band ESR spectrometer (JEOL, Japan) equipped with a JEOL ES-CT470 cryostat. A Quantum Design MPMS-XL SQUID magnetometer (Quantum Design, UK) was used to measure static magnetic susceptibility of 1 at 1 kOe magnetic field in cooling and heating conditions in the 300–1.9 K range. A sample holder contribution was subtracted from the experimental values. Curie constant (C), Weiss temperature (Θ), and temperature-independent contribution (χd) were estimated by the following expression: χM = C/(T − Θ) + χd. Effective magnetic moment (μeff) was calculated using the following formula: μeff = (8·χM·T)1/2. H3Hhp was prepared according to ref 23. Anhydrous Dy3+(TMHD)3 (TMHD: 2,2,6,6-tetramethyl-3,5-heptanedionate) (>98%) was purchased from Strem Chemicals, Inc. (Shanghai, China) and decamethylcobaltocene (Cp*2Co) was purchased from Sigma-Aldrich (USA). o-Dichlorobenzene (C6H4Cl2; Acros Chemicals, Shanghai, China) was distilled over CaH2 under reduced pressure and n-hexane was distilled over Na/benzophenone. Solvents were degassed and stored in an MBraun 150B-G glove box (Germany). Salt 1 was synthesized and stored in the glove box with a controlled atmosphere containing less than 1 ppm of water and oxygen. KBr pellets used for IR and UV–vis–NIR analyses were prepared in the glove box. Magnetic measurements were performed on a polycrystalline sample of 1 sealed in a 2 mm quartz tube under ambient pressure under anaerobic conditions. Synthesis of 1 Crystals of (Cp*2Co){Dy3+(TMHD)2(Cl)(H2Hhp)}·2C6H4Cl2 ( 1) were obtained via the reaction of H3Hhp (14.2 mg, 0.021 mmol) with three equivalents of Dy3+(TMHD)3 (45 mg, 0.063 mmol) in the presence of one equivalent of Cp*2Co (7 mg, 0.021 mmol) in 16 mL of o-Dichlorobenzene (o-DCB) upon stirring at 50 °C for 24 h. The starting H3Hhp material was insoluble in C6H4Cl2; however, after 24 h, H3Hhp completely dissolved to give a red-brown solution. The solution obtained was cooled down to RT and filtered into a 1.8-cm-diameter 50 mL glass tube with a ground glass plug, and then 30 mL of n-hexane was layered over the solution. Slow mixing of the solutions over 1 month resulted in precipitation of the crystals. The solvent was then decanted from the crystals and washed with n-hexane. Black-brown plates of 1 were obtained in 54% yield. The composition of the obtained crystals was determined by X-ray diffraction analysis of a single crystal. Several crystals from one synthesis were found to consist of a single crystalline phase. The composition of the obtained crystals was determined from X-ray diffraction analysis on a single crystal. Several crystals from one synthesis were found to belong to a single crystalline phase. Elemental analysis supported the determined composition. Anal. Calcd. for C84H90Cl5CoDyN15O4S3, Mr = 1868.56: C, 54.00; H, 4.82; N, 11.24, Cl 9.50. Found: C, 53.74; H, 4.56; N, 11.02; Cl 9.92. X-ray crystal structure determination X-ray diffraction data for 1 at 110(2) K were collected on an Oxford diffraction "Gemini-R" CCD diffractometer (Oxford, UK) with graphite monochromated MoKα radiation using an Oxford Instrument Cryojet system. Raw data reduction to F2 was carried out using CrysAlisPro (Oxford Diffraction Ltd., UK).24 The structures were solved by direct method and refined by the full-matrix least-squares method against F2 using SHELX 2018/3.25 Nonhydrogen atoms were refined in the anisotropic approximation. Crystal data for 1 at 150.00(14) K: C84H90Cl5CoDyN15O4S3, F.W. 1868.56, dark black block, 0.565 × 0.132 × 0.068 mm, orthorhombic phase with space group P bcm, a = 10.4531(3), b = 30.2423(8), c = 28.5373(8) Å, α = β = γ = 90°, V = 9021.4(4) Å3, Z = 4, dcalcd = 1.376 M gm−3, μ = 1.279 mm−1, F(000) = 3828, 2θmax = 59.352°; 40331 reflections collected, 8110 independent; R1 = 0.0821 for 6009 observed data [>2σ(F)] with 364 restraints and 642 parameters; wR2 = 0.2212 (all data); final GoF = 1.105. CCDC 2264332. Crystal structure of 1 contained half of independent Cp*2Co+ cation and the {DyIII(TMHD−)2(Cl−)(H2Hhp−)}− anion. One tert-Bu group of DyIII(TMHD)2 was disordered between two orientations with 0.694(12)/0.306(12) occupancies. One of five CH3 groups of Cp*2Co+ is statistically disordered between two orientations. Also, there were two independent solvent C6H4Cl2 molecules which had only 0.5 occupancies. One molecule was statistically disordered between two orientations, whereas there were two orientations for the second molecule with 0.435(4)/0.065(4) occupancies. To keep the anisotropic thermal parameters of the disordered solvent atoms within reasonable limits, the displacement components were restrained using ISOR, SIMU, and DELU instructions from SHELXL program26 from the X-ray diffraction data. This resulted in the 364 restraints used for the refinement of crystal structures of 1. Computational details All reported structures were optimized at density functional theory (DFT) level using the Becke, 3-parameter, Lee–Yang–Parr (B3LYP)27 functional and the standard 6-31G(d,p) basis set for C, N, S, Cl, O and H. As much as 60-electron Stuttgart-Bonn relativistic pseudopotentials were used for Dy.28 The ultrafine integration grid was employed. No symmetry constraints were imposed. The calculations were performed considering a multiplicity of S = 6. Analytical harmonic frequencies were computed at the same level of theory to confirm the nature of the stationary points. All of the calculations were carried out by the methods implemented in the Gaussian 16 package.29 Time-dependent density functional theory (TD-DFT) calculations were carried out at the CAM-B3LYP30 level of theory using the basis set previously employed for optimization. Results and Discussion The synthetic approach towards the formation of Dy3+-H3Hhp complexes is depicted in Figure 2. As a Dy3+ source, we selected Dy3+(TMHD)3 due to (1) its stability and good solubility in organic solvents; (2) the labile coordination of TMHD to the metal, which facilitated the exchange with the chelate; and (3) the capability of TMHD ligand to deprotonate the macrocycle during the complexation, thereby releasing TMHD. Simultaneously, reducing conditions (i.e., decamethylcobaltocene: Cp2*Co+) were employed to ensure the solubility of the large and planar H3Hhp macrocycle. This strategy has been widely employed for the synthesis of crystalline porphyrinoid-based complexes with intriguing coordination environments.31–33 On this basis, H3Hhp was reacted with three equivalents of Dy3+(TMHD)3 and one equivalent of Cp2*Co+, in C6H4Cl2 at 50 °C. This process led to the complete solubilization of the macrocycle and the formation of a red-brown solution which, after mixing with n-hexane, afforded crystals in a 54% yield. Remarkably, elemental analysis on these crystals revealed a (Cp*2Co){Dy(TMHD)2(Cl)(H2Hhp−)}·3C6H4Cl2 composition, with H2Hhp− being H3Hhp but with one less hydrogen atom. Figure 2 | Synthesis of Dy-H3Hhp complex 1. Download figure Download PowerPoint To unambiguously elucidate the structure of the obtained compound, hereafter referred to as 1, their crystals were then analyzed by single-crystal X-ray diffraction. As shown in Figure 3a,b, 1 consisted of a Dy-H3Hhp complex, presenting off-centered coordination to a Dy atom through one isoindolic nitrogen and two nitrogen atoms of two different thiadiazol rings. Notably, this coordination mode was similar to that of previously observed on-surface. The Dy-H3Hhp complexes were surrounded by Cp*2Co+ molecules, and the nitrogen atoms of isoindole subunits not involved in the coordination remained protonated. Thus, the macrocyclic ligand is formally the deprotonated form of H3Hhp (H2Hhp−). The Dy atom, in turn, coordinated two TMHD ligands and, remarkably, a chlorine atom, which probably abstracted from the C6H4Cl2 used as the solvent. Similar abstraction processes have also been found in the synthesis of {Cryptand(Li+)}2{Li3Cl(Hhp)}2.32 In our case, the driving force seemed to be the strong tendency of the Dy atom to exhibit a coordination number of 8 or even higher, which, without chloride coordination would be 7. Analysis of the local symmetry of Dy3+ in 1 at 150 K using Shape34,35 indicated that the surrounding Dy3+ was rather far from any known polyhedral since all continuous shapes measures (CShM) values obtained by Shape are rather large (see Supporting Information Table S3). Infrared (IR) spectra of complex 1 and the starting components are given in Supporting Information Figure S1. The spectrum showed the presence of all components found in the complex. Bands of H3Hhp were shifted up to 12 cm−1 due to deprotonation and formation of the complex with Dy3+. Figure 3 | (a) X-ray structure and (b) crystal packing of 1. Atom color code of (a): carbon in gray, nitrogen in blue, hydrogen in white, oxygen in red, chlorine in purple, sulfur in pale yellow, and dysprosium in dark yellow. Orange and purple molecules in the packing correspond to Dy-H2Hhp and Cp*2Co fragments, respectively. Download figure Download PowerPoint Collectively, we inferred that 1 is based on a (Cp*2Co+){Dy3+(TMHD)2(Cl)(H2Hhp−)}− ion pair, where the negative charges of the ligands were compensated by Dy3+ and Cp*2Co+. This suggested that neither the macrocycle nor Dy3+ had been reduced. To get further structural insights into this off-centered Dy3+ complex, we went deeper into its structural analysis. Crystal structure of 1 contained half of independent Cp*2Co+ and {Dy3+(TMHD)2(Cl)(H2Hhp−)}− ions and one and a half independent C6H4Cl2 molecules. The geometry of the Dy3+ ions was square antiprismatic, although distorted due to the different lengths of the Dy-O (2.29–2.33 Å), Dy-Cl (2.410(3) Å) and Dy-N bonds with pyrrole and thiadiazole nitrogen atoms (2.489(3) and 2.561(3) Å, respectively). The Dy3+ center was positioned above the plane of three coordinated nitrogen atoms by 1.557 Å. As observed with Dy-Ps and Dy-Pcs complexes, this was ascribed to the large size of the Dy3+ ion, which prevented its insertion into the H2Hhp− cavity. On the other hand, the chloride atom was oriented toward the isoindolic N–H groups, presenting Cl-H distances within the range of H-bonding interactions. Regarding the macrocycle, this coordination mode induced a planarity deviation of the H2Hhp− core, leading to a bowl-like structure. It is important to highlight that the geometry of H2Hhp− anion is still unknown. However, as shown in Supporting Information Table S2, most bond lengths of 1 were similar to that of H3Hhp since the number of π-conjugated electrons does not change. Interestingly, in crystal packing, it is observed that Cp*2Co+ cations and {Dy3+(TMHD)2(Cl)(H2Hhp−)}− anion organize into an alternate fashion. This was governed by π–π between and the of to the Dy3+ As both Cp*2Co+ and H2Hhp− groups were magnetic coupling by Cp*2Co+ is not the properties of 1 were explored by between spectra of 1, and that of H3Hhp are shown in Figure H2Hhp− two at and and a at about complex 1 exhibited two at and and a at about This result was in with the fact that the deprotonation without The of further supported that the macrocycle was not as it would result in the molecular and the of from to The very and at nm was to from the π–π between and Cp*2Co+ As observed by calculations (see Supporting Information for further the observed were from between three and three which were in the macrocycle. Figure | (a) of the starting H3Hhp material and complex 1 in the UV–vis–NIR range in KBr 1 was prepared in anaerobic conditions. (b) calculated molecular of 1 involved in the observed in the and are whereas and are density functional Download figure Download PowerPoint Remarkably, despite using three equivalents of the final only one Dy atom. This was considering that the H2Hhp− still coordination to at least one further Dy atom. To on the origin of this intriguing we performed theoretical calculations (see Supporting Information for further the theoretical structures of complexes coordinating two Dy atoms were and the complexation were this was to have a on the complexation the cation was from the to the of these binuclear complexes, two coordination were wherein both Dy atoms a coordination number of 8 and were through two chloride wherein the Dy atoms are through one chloride thereby one Dy atom a coordination number of the other was 8. The structures and their complexation are in Figure Interestingly, the Dy complexation (i.e., from H3Hhp to 1) was found to be the second one was determined to be of the formed was or As in Figure the macrocyclic in 1, less planar than still for efficient between the different and exhibited a from wherein the structure of Dy a Based on we that the coordination of a second Dy atom did not as it would have the within the macrocycle and of the Dy coordination complex. Figure | calculated the and molecular structures of the complexation of Dy3+ atoms to the H3Hhp macrocycle. Atom color code of (a): carbon in nitrogen in blue, hydrogen in white, oxygen in red, chlorine in purple, sulfur in pale yellow, and dysprosium in dark yellow. density functional Download figure Download PowerPoint the magnetic of 1, its magnetic properties were as a polycrystalline sample sealed under in the In the to Dy3+ were due to the for which is much than the of a at the X-band only a and was observed ( Supporting Information and to the contribution of of S = that it from The had a of and a of at K and into two K. the parameters of the components were = = and = = Based on these it could be that were on the Dy3+ ion has the at = magnetic moment of 1 was found to be at similar to the calculated magnetic moment for Dy3+ ion The magnetic moment of 1 was temperature-independent (Figure of magnetic susceptibility was which for the determination of a Weiss temperature of K ( Supporting Information Figure S3). This indicated only coupling of in 1. As previously the paramagnetic Dy3+ ions were completely by As a the between the paramagnetic centers was Å, which only magnetic coupling of The was even at 1 magnetic field the of (Figure This was up to was not observed in 1 at 2 K under of the magnetic On the other hand, properties at magnetic showed that 1 was not a single ion since were observed in the temperature of and at We ascribed this of magnetic to the distorted geometry of Dy3+. showed that the of Dy3+ was rather far from square ( Supporting Information Table S3). Figure | (a) of the magnetic moment of polycrystalline 1 measured in the K (b) of magnetic field up to 50 kOe is a to the for polycrystalline 1. Download figure Download PowerPoint In this work, we have that H3Hhp is a ligand for magnetically active Dy3+ In this we found that performing complexation under reductive conditions is a powerful strategy to the without the oxidation state of the expanded As observed by X-ray diffraction analysis, the H3Hhp macrocycle was found to one Dy3+ atom, despite using an of the Dy3+ source. calculations suggested that the coordination of an Dy3+ atom would the macrocycle and The mononuclear complex 1, was found to exhibit an off-centered, out-of-plane as as a supramolecular by π–π with Cp*2Co molecules. This the magnetic coupling between the Dy3+ the electronic properties of the H3Hhp macrocycle remained after this work provides key insights into the coordination of magnetically active metals with expanded porphyrinoids, which the development of toward more complex with different and coordination are in our Supporting Information Supporting Information is and IR magnetic X-ray and molecular of is of to from the Russian for the synthesis and of and magnetic properties of 1. The analysis of the IR spectra was supported by the of and of the Russian number and from the of and of the Russian for synthesis of H3Hhp and calculations. from the the de Madrid, and the State through the and and the through the de from the for of in de also the Dysprosium ; Porphyrin ; Crystallography ; Plane (geometry) ; Materials science ; Chemistry ; Photochemistry ; Inorganic chemistry ; Geometry ; Mathematics Porphyrin and Phthalocyanine Chemistry