# Embedding Mo 2 O 2 S 2 -Bis(thiosemicarbazone) Complexes Into Polyurethane Matrices: Synthesis and Characterization

Diana Cebotari, Roa Alchamandi, Yann Molard, Maria Amela-Cortes, Carine

Livage, Mohamed Haouas, Jérôme Marrot, Aurelian Gulea, Cyril Gorny,

Bruno Fayolle, et al.

► To cite this version:

Diana Cebotari, Roa Alchamandi, Yann Molard, Maria Amela-Cortes, Carine Livage, et al. Embedding Mo 2 O 2 S 2 -Bis(thiosemicarbazone) Complexes Into Polyurethane Matrices: Synthesis and Characterization. Journal of Polymer Science, 2025, 10.1002/pol.20240556. hal-04990328

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Submitted on 13 Mar 2025

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# Embedding Mo₂O₂S₂-bis(thiosemicarbazone) complexes into polyurethanes matrices: synthesis and characterization

Sergiu Calancea<sup>a,*</sup>, Diana Cebotari<sup>a,b</sup>, Roa Al Chamandi<sup>a,c</sup>, Yann Molard<sup>d</sup>, Maria Amela-Cortes<sup>d,∗</sup>, Carine Livage<sup>a</sup>, Mohamed Haouas<sup>a</sup>, Jérôme Marrot<sup>a</sup>, Aurelian Gulea<sup>b</sup>, Cyril Gorny<sup>e</sup>, Bruno Fayolle<sup>e</sup>, Sébastien Floquet<sup>a,∗</sup>

## ARTICLE INFO

### Keywords:

[MoV₂O₂S₂]²⁺
thiosemicarbazone
Polyurethane

## ABSTRACT

The [MoV₂O₂S₂]²⁺-based thiosemicarbazone complexes are an interesting family of molecules, which can display various biological properties. However, in order to develop applications, it is necessary to shape this type of complexes, in polymer matrices for example. In this article, we report the synthesis of a series of 16 composite materials corresponding to the incorporation of [(MoO₂O₂S₂)ₙ(L¹⁻⁶)ₙ] (n = 1, 2) bis-thiosemicarbazones complexes in a polyurethane matrix. These composites are described as [MoV₂O₂S₂]²⁺-based polyurethanes and denoted PU-[(MoO₂O₂S₂)ₙ(L¹⁻⁶)ₙ] (n = 1, 2). Various [(MoO₂O₂S₂)ₙ(L¹⁻⁶)ₙ] bis-thiosemicarbazone complexes were used including di- or tetranuclear structures with different number of uncoordinated amino and hydroxyl groups and alkyl substituents on the ligands L¹ (i = 1 to 6). The composite materials obtained are studied in depth by SEM-EDX, FT-IR, NMR, TGA and DSC to understand the organization of polymer chains and complexes within the materials, and to highlight certain changes in physical properties induced by the nature of the complexes. The complexes are homogeneously distributed within the polymer matrices and the embedding of these complexes seems to be mainly due to hydrogen bonding networks. Nevertheless, these H-bond networks are strong enough to provoke modification of the physical properties of the polymers in terms of thermal stability or flexibility.

## 1. Introduction

The [MoV₂O₂S₂]²⁺ cluster can be easily associated with plethora of inorganic and organic ligands giving rise to a wide panel of compounds with various nuclearities and properties in biology, catalysis or electrocatalysis [1]. When coordinated to polycarboxylates, amino-acids or thiosemicarbazone ligands, this molybdenum cluster exibits interesting medicinal and biological properties. In particular, Suman's group reported [MoV₂O₂S₂]²⁺-based complexes with different aminoacids to be efficient against cyanide poisoning [2] and others based on phosphinoyldithioformate ligands as catalyst in sulfur atom transfer reactions [3]. On our side, we reported complexes with polycarboxylate and thiosemicarbazone ligands and investigated their properties revealing, for some complexes, good or very good antioxidant, antifungal, antibacterial or antitumoral activities [4]. However, the stability of these complexes is not very high, which is a major limitation for applications.

In this context, and with a view to developing practical applications, homogeneous dispersion of [MoV₂O₂S₂]²⁺-thiosemicarbazones complexes in a polymer matrix may be one strategy for stabilizing them. To our knowledge, only a few examples of Mo complexes-based polymers have been reported [5-9]. The Mo-complex composites can be covalently bonded [5,6,8,9] or embedded [7] in a polymer matrix. These polymers show

catalytic [5], gas absorption [7] and optical promising properties [8,9], which prompted us to explore this strategy. For this purpose, a series of [(MoO₂O₂S₂)ₙ(L¹⁻⁶)ₙ] (n = 1 or 2) complexes, resulting from the reaction of [MoV₂O₂S₂]²⁺ cluster with a serie of selected bis-thiosemicarbazone ligands H₂L¹⁻⁶ (see **scheme 1**; the ligands are twice deprotonated upon coordination with [MoV₂O₂S₂]²⁺ cluster).

<figure><img src="image_2.png" /><figcaption>**Scheme 1.** The selected bis-thiosemicarbazone ligands with flexible and rigid spacers used in this study for the synthesis of [(MoO₂O₂S₂)₂(L¹⁻²)] and [Mo₂O₂S₂(L³⁻⁶)₂] complexes respectively.</figcaption></figure>

<footnote><sup>a</sup> Institut Lavoisier de Versailles, CNRS, UVSQ, Université Paris-Saclay, 45 av. des Etats-Unis, 78035 Versailles, France</footnote>

<footnote><sup>b</sup> State University of Moldova, 60 Alexei Mateevici str., MD-2009 Chisinau, Republic of Moldova</footnote>

<footnote><sup>c</sup> EDST, Université Libanaise, Campus Hariri, Hadath, Beyrouth, Lebanon</footnote>

<footnote><sup>d</sup> Université de Rennes, CNRS, ISCR – UMR 6226, Rennes F-35000, France</footnote>

<footnote><sup>e</sup> PIMM, Arts et Metiers Institute of Technology, CNRS, Cnam, HESAM University, 151 Boulevard de l'Hopital 75013 Paris, France</footnote>

<footnote>* Corresponding authors at: Institut Lavoisier de Versailles, CNRS, UVSQ, Université Paris-Saclay, 45 av. des Etats-Unis, 78035 Versailles and Université de Rennes, CNRS, ISCR – UMR 6226, Rennes F-35000, France</footnote>

<footnote>E-mail address: sebastien.floquet@uvsq.fr (S. Floquet), sergiu.calancea@uvsq.fr (S. Calancea), maria.amela-cortes@univ-rennes.fr (Maria Amela-Cortes)</footnote>
The ligands H₂L¹⁻² with flexible spacers lead to dinuclear complexes while the rigid ones H₂L³⁻⁶ lead to tetranuclear compounds as reported in our previous work for [(Mo₂O₂S₂)(L')] and [(Mo₂O₂S₂)₂(L⁴)₂] complexes [10]. The complexes obtained with the other ligands (H₂L²,³,⁵,⁶) are reported herein and characterized for the first time in this study. The objective of this selection is to evaluate the contribution of different functionalities on the ligand as the number of amino and hydroxyl groups and the presence or the lack of alkyl fragments on structural organization of the composite materials we target.

## 2. Experimental section

### 2.1. Materials and methods

All chemicals were analytical grade and used without any further purification. FT-IR spectra were recorded on a 6700 Fourier Transform Nicolet spectrophotometer (ATR Diamond) in the range 400-4000 cm⁻¹. The elemental analyses (C, H, N, S) were performed by BioCIS laboratory, University Paris-Saclay (www.biocis.universite-paris-saclay.fr), Orsay, France.

#### MALDI-TOF MS analyses

The spectrum for [Mo₂O₂S₂(L²)] was performed on powder in linear positive ion mode using UltrafleXTreme mass spectrometer (Bruker Daltonics, Bremen) calibrated with polyethylene glycol (PEG) based polymers, PEG1500 and PEG4500. The spectrum was processed using Bruker Daltonics FlexAnalysis program. The dithranol used as the matrix was purchased from Sigma Aldrich Co. The sample was prepared by adding 60 µM THF-DMSO solution to 6 mM matrix-sodium salt solution, in a volume ratio of 1 : 9. The powder obtained after drying was analyzed using MALDI-TOF technique. The MALDI-TOF spectrum was simulated in IsoPro 3.1. available as freeware on https://sites.google.com/site/isoproms/home.

#### Nuclear magnetic resonance

¹H, ¹³C, ¹⁵N{¹H} and ¹³C{¹H} HMBC, ¹H-¹H COSY, ¹³C{¹H} HSQC, ¹H-¹H NOESY spectra of neat PU (polyurethane polymer) and the [Mo₂O₂S₂(L²)] complex were performed at 296 K on a Bruker Avance 400 MHz spectrometer with a 5 mm BBI probe head at 9.4 T. The ¹H spectra of neat PU, [(Mo₂O₂S₂)n(L¹⁻⁶)n] (n = 1 or 2) complexes and the solutions obtained from solubility test of PU-[(Mo₂O₂S₂)n(L¹⁻⁶)n] polymers in DMSO solvent, were recorded at 298 K on Bruker Avance 300 MHz spectrometer. All samples were solubilized in DMSO-d₆ deuterated solvent, excepting in the case of solubility tests for PU-[(Mo₂O₂S₂)n(L¹⁻⁶)n] polymers: to DMSO solutions obtained after swelling were added few drops of DMSO-d₆ deuterated solvent. Chemical shifts are reported to tetramethylsilane (TMS) as internal standard and neat nitromethane (NM) for ¹⁵N{¹H} HMBC spectra.

#### Single crystal X-ray diffraction

The single-crystal X-ray diffraction data were collected for compounds [(Mo₂O₂S₂)₂(L³)₂], [(Mo₂O₂S₂)₂(L⁵)₂] and [(Mo₂O₂S₂)₂(L⁶)₂] on a Bruker Apex Duo diffractometer with molybdenum radiation (MoKα, λ = 0.71073 Å) by doing φ and ω scans of narrow (0.5°) frames at 200 or 230 K. The empirical absorption correction was applied using the SADABS program [11]. The structures were solved by direct method and refined by full-matrix least-squares treatment against |F|² in anisotropic approximation with SHELX 2014/7 set12 using ShelXle program [13]. Crystallographic data including more details about crystal structure determination have been deposited at the Cambridge Crystallographic Data Center: CCDC-xxx ([(Mo₂O₂S₂)₂(L³)₂]), CCDC-xxx ([(Mo₂O₂S₂)₂(L⁵)₂]) and CCDC-xxx ([(Mo₂O₂S₂)₂(L⁶)₂]).

#### Scanning electron microscope (SEM) and Energy Dispersive X-ray (EDX) Spectroscopy

All PU-[(Mo₂O₂S₂)n(L¹⁻⁶)n] samples were gold-plated and analyzed at JSM 7001F scanning electron microscope.

#### Thermogravimetric analysis (TGA)

The TGA analysis was recorded on a Seiko TG/DTA 320 thermogravimetric balance. The samples were measured under O₂ between room temperature and 700 °C (scan rate: 5 °C.min⁻¹).

#### Differential Scanning Calorimetry (DSC) analyses

The DSC measurements were performed on a DSC25 (Waters, TA Instruments) calorimeter. The weighed samples (5 mg) were twice thermally cycled from in the range -85 to +150 °C under nitrogen flow at a rate of 10 K min⁻¹.

#### Swelling measurements

Swelling measurements were performed in toluene at room temperature according to reported procedure [14]. The weighed round pieces cut from the main samples (m_b) were immersed in toluene at room temperature during 4 days until they reach equilibrium. The swelled-samples were patted with paper and reweighed (m_s) and then, dried in the oven at 80 °C during 72 h until they reached stable mass (m_d). The density values of polymer samples (ρ_b) were determined employing a density balance XS203S Mettler Toledo (+/- 0.005 g) employing the double weighing method: in the air and in the water. The swelling degrees based on the solvent uptake (SDSU) and on the increase in polymer volume (SDIV) were calculated according to Eq. 1 and 2 respectively [15,16].

$$SD_{SU} = \frac{m_s - m_b}{m_b} \times 100 \quad (1)$$

$$SD_{IV} = \frac{\frac{m_b}{\rho_p} + \frac{m_s - m_d}{\rho_s}}{\frac{m_b}{\rho_p}} \quad (2)$$

The soluble fractions (F_s) of polymers in the swollen state were found according to the following equation:

$$F_s(\%) = \frac{m_b - m_d}{m_b} \times 100 \quad (3)$$

### 2.2. Synthesis of the ligands, complexes and composites

The ligands H₂L¹ and H₂L⁴ have been obtained according to published procedures [10]. The ligands H₂L², H₂L³, H₂L⁵ and H₂L⁶ reported in literature [17,18,19,20] have been obtained by modified procedure given in the supporting information (SI).

The [(Mo₂O₂S₂)n(L¹⁻⁶)n] (n = 1 or 2) complexes have been obtained by published procedure using corresponding bis(thioemicarbazone) H₂L²-H₂L⁶ ligands and the cyclic compound K₂⁻(NMe₄)₃[1₂Mo₁₀O₁₀S₁₀(OH)₁₀(H₂O)₅]·20H₂O (called hereafter Mo₁₀) used as precursor (see details in the SI) [10]. All complexes described in this work excepting [(Mo₂O₂S₂)₂(L⁴)₂] and [Mo₂O₂S₂(L')₂] [10] compounds are not previously reported. The ligands and complexes have been characterized by ¹H NMR and FT-IR spectroscopy (Figures. S1-S6, SI), and elemental analysis, and all complexes excepting [Mo₂O₂S₂(L²)], were analyzed by single crystal X-ray diffraction (Table S2, SI). The [Mo₂O₂S₂(L²)] complex was analyzed by MALDI-TOF technique. The MALDI-TOF spectrum obtained on powder in the positive mode is reported in Figure S7 (SI). The spectrum is presenting the main isotopic peak centered at 754.69 (m/z) corresponding to the monocationic addendum between the neutral dinuclear species [Mo₂O₂S₂(L²)] and Na⁺.

The syntheses of the PU-[(Mo₂O₂S₂)n(L¹⁻⁶)n] polymer composites have been performed accordingly to the procedure given in SI, using 1,6-hexamethylene diisocyanate (HDI), PEG, 1,4-butandiol (BD) and [(Mo₂O₂S₂)n(L¹⁻⁶)n] complexes. They were characterized by EDX/SEM and FT-IR spectroscopies (Figures. S9-S30, SI), TGA (Figures. S39-S45, SI), DSC (Figures. S46-S51, SI) and Swelling measurements.

## 3. Results and discussion

### 1.1. Synthesis and structures of the [(Mo₂O₂S₂)n(L¹⁻⁶)n] (n = 1 or 2) complexes

The [Mo₂O₂S₂(L¹⁻²)] and [(Mo₂O₂S₂)₂(L³⁻⁶)₂] complexes were
obtained by reaction in DMF of Mo<sub>10</sub> precursor with H<sub>2</sub>L<sup>1-6</sup> ligands and isolated as powder or single crystals. The crystal structures of [Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>1</sup>)] and [(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>3-6</sup>)<sub>2</sub>] are shown in **Figure 1**, while

[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>2</sup>)] could not be obtained as single crystals.

<figure><img src="image_3.png" /><figcaption>**Figure 1.** Molecular structures of [Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>1</sup>)]<sup>10</sup>, [(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>3</sup>)<sub>2</sub>], [(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>4</sup>)<sub>2</sub>]<sup>10</sup>, [(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>5</sup>)<sub>2</sub>], and [(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>6</sup>)<sub>2</sub>]. Colour code: Mo (blue), C (gray), O (red), N (green), and S (yellow).</figcaption></figure>
The [(Mo₂O₂S₂)₂(L³)₂], [(Mo₂O₂S₂)₂(L⁵)₂] and [(Mo₂O₂S₂)₂(L⁶)₂] complexes have been isolated as yellow crystals by slow evaporation of DMF solution after several days. The molecular structures of these complexes are given in **Figure 1** in comparison with those of [Mo₂O₂S₂(L¹)] and [(Mo₂O₂S₂)₂(L⁴)₂], already published [10]. The crystallographic data are given in the supporting information (**Table S2**). The MoV atoms are found in distorted square pyramid geometry linked in the axial positions by oxo ligands and in equatorial positions by two µ-sulfido atoms and N/S atoms of the bis-thiosemicarbazones ligands. The Mo-Mo, Mo-S and Mo=O bond distances are in the ranges 2.83-2.85, 2.31-2.33 and 1.67-1.68 Å, respectively, consistent with the [Mo₂O₂S₂]²⁺ cluster structure [1a,1b]. The asymmetric units of the dinuclear complex [Mo₂O₂S₂(L¹)] consist of one [Mo₂O₂S₂]²⁺ cluster linked to one bis(bidentate)bis-thiosemicarbazone ligand (**Figure 1**). In the rectangular shaped tetranuclear complexes, [(Mo₂O₂S₂)₂(L³)₂], [(Mo₂O₂S₂)₂(L⁴)₂], [(Mo₂O₂S₂)₂(L⁵)₂], and [(Mo₂O₂S₂)₂(L⁶)₂], the two [Mo₂O₂S₂]²⁺ clusters are coordinated to two bis-thiosemicarbazone ligands (**Figure 1**). As usual for this type of molybdenum(V) complexes the bis-thiosemicarbazone ligands are twice deprotonated (L²⁻) being coordinated to metal ions by thiolate and azomethinic nitrogen atoms. The deprotonation of the ligands is confirmed by C-S and C-N bond distances. The average C-S bond distance is higher in the complexes (1.74 Å) than in uncoordinated ligands (1.65-1.70 Å) and thus corresponding to the single bond [21]. In contrast, the C-N bond distance in the complexes is shorter (1.33 Å) than in free thiosemicarbazones (1.35 Å), corresponding to the C=N double bond [22]. The average Mo-S ligand bond distances of 2.46 Å is consistent with Mo(V) oxidation state [23].

As seen in **Figure 1**, the di- and tetra-nuclear complexes contain two or four amino groups, respectively, which could react with HDI to form ureido-linkages. Furthermore, the [Mo₂O₂S₂(L²)], [(Mo₂O₂S₂)₂(L⁵)₂] and [(Mo₂O₂S₂)₂(L⁶)₂] complexes have additional phenolic or hydroxyl groups that can react with urethane to form bonds. On the other hand, the [(Mo₂O₂S₂)₂(L⁴)₂] and [(Mo₂O₂S₂)₂(L⁶)₂] complexes contain tert-butyl and methyl groups, respectively, which can induce hydrophobic interactions in the polymer matrix.

The FT-IR and NMR spectra (**Figures S1-S6**) are given in the SI as well as the elemental analyses. The ¹H NMR spectra of all complexes are in agreement with X-ray structures showing twice deprotonated bis-thiosemicarbazone ligands. The [Mo₂O₂S₂(L²)] complex has been obtained as yellow powder. The [Mo₂O₂S₂(L²)] complex only differs from [Mo₂O₂S₂(L¹)] by the nature of the flexible spacer, which is shorter in [Mo₂O₂S₂(L²)] and contains an additional -OH function. The ¹H-NMR spectrum of the [Mo₂O₂S₂(L²)] is given in **Figure 2** in comparison with the [Mo₂O₂S₂(L¹)] complex for which the crystallographic structure is published [10]. The spectrum agrees with a 80/20 mixture of two isomer complexes of formula [Mo₂O₂S₂(L²)] in which the OH group could occupy two positions, i.e., cis or trans in regards with the orientation of the Mo=O bonds of the [Mo₂O₂S₂]²⁺ cluster. The proton assignments were based on ¹H-¹H COSY (**Figure S5**, SI) and NOESY (**Figure S6**, SI) correlations.

<figure><img src="image_4.png" /><figcaption>A</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>**Fig. 2.** ¹H NMR (DMSO-d₆) spectra of [(Mo₂O₂S₂)₂(L²)] (A) and [(Mo₂O₂S₂)₂(L¹)] (B) [10].</figcaption></figure>

### Synthesis of the PU-[(Mo₂O₂S₂)n(L¹⁻⁶)n] polymers

The PU-[(Mo₂O₂S₂)n(L¹⁻⁶)n] polymers have been obtained by one-step method keeping constant PEG and BD quantities while varying the HDI and [(Mo₂O₂S₂)n(L¹⁻⁶)n] ones as described in SI (**Table S1**). The polyurethane-based composites were obtained with 1, 3 and 5 wt% of [(Mo₂O₂S₂)n(L¹)n] (i = 1, 2, 4, 5, or 6) complexes. The low solubility of [(Mo₂O₂S₂)₂(L³)₂] complex in THF allows the synthesis of polyurethane only at 1% complex content. The chemical reaction is depicted in **Figure 3A**. The end of polymerization was confirmed by FT-IR spectroscopy with the lack of NCO vibration band of HDI at 2270 cm⁻¹ (**Figures S25-S30**, SI). The polymers were obtained as transparent or as translucid homogeneous yellow solids (**Figure 3B**, and **Figure S8**, SI) which suggests that the [(Mo₂O₂S₂)n(L¹⁻⁶)n] complexes are homogeneously integrated into polymer matrix without degradation. The PU-[(Mo₂O₂S₂)n(L¹⁻⁶)n] polymers have been further characterized by FT-IR, and SEM/EDX. The thermal properties have been investigated by TGA and DSC measurements. The swelling analysis was also performed using toluene as solvent.

### SEM/EDX analysis

The SEM and EDX measurements have been performed for all polyurethane samples. **Figure 4** shows SEM images, EDX dot maps for the Mo and S elements, and EDX spectrum for the PU-5%-[(Mo₂O₂S₂)₂(L⁶)₂] polyurethane. The data for other polyurethanes are reported in SI (**Figures S9-S24**, SI). As a general feature for all composite materials in this study, the EDX dot maps and spectra confirm the presence of homogeneously distributed Mo and S elements in the polymer, with a Mo/S atomic ratio around 1/2 as expected from the complexes formulas.

### Infrared spectroscopy analysis

As the concentration of the complexes in the PU-[(Mo₂O₂S₂)n(L¹⁻⁶)n] is very low, the polymers are showing similar FT-IR spectra as neat PU. FT-IR spectra of polyurethanes are reported in SI (**Figures S9-S24**).
S25-S30). In the **neat PU** (Figure 5) a medium absorption peak at 3322 cm⁻¹ with a shoulder at 3524 cm⁻¹ are observed. The first absorption can be assigned to the N-H stretching involved in the hydrogen bonding with i) C=O linkage from urethane groups (N-H...O=C) and ii) with ether groups (N-H...O) of PEG fragments (Table S3, SI) [24,25]. The second band at 3524 cm⁻¹ is related to the free N-H groups [24,25]. Additionally, the N-H bending stretching shows an absorption peak at 1540 cm⁻¹ [24]. Two absorption bands centered at 2873 and 2940 cm⁻¹ are attributable to the symmetric and asymmetric methylene vibrations, respectively [24]. The C=O linkage shows two bands at 1684 and 1716 cm⁻¹. The first band corresponds to C=O...NH(C=O) hydrogen bonding in hard segments (H-bonded C=O band) while the second, to the free C=O group, C=O...NH(C=O) (Table S3, SI) [24,25]. The large band with two maxima at 1136 and 1108 cm⁻¹ can be assigned to C-O-C vibrations of urethane and/or ether groups [25]. Finally, the absorption peak at 1267 cm⁻¹ can be associated to the N-H bending and C-N elongation stretching [25].

The amount of hydrogen-bonding or hydrogen bonding index (HBI) of amino and carbonyl groups was calculated according to the equation (4) [ref], were A<sub>HB</sub> is the area of the absorption band of corresponding hydrogen-bonding group while A<sub>free</sub>, to area of free groups.

$$ \text{HBI (\%)} = \frac{A_{\text{HB}}}{A_{\text{HB}} + A_{\text{free}}} \times 100 \quad (4) $$

All HBI values are given in Table S3, SI. Compared to the **neat PU**, the HBI values for all PU-[(Mo₂O₂S₂)ₙ(L¹⁻⁶)ₙ] polymers are higher for N-H groups and lower for C=O groups. This means that the

complexes are disturbing intermolecular hydrogen bonding of polyurethane chains mostly on hard segments: N-H...O=C. The increase of HBI says that more N-H groups are involved in Mo=O...H-N intermolecular hydrogen bonding with the complexes. Therefore, less C=O groups are bound in hard-segment N-H...O=C and thus lowering HBI values.
A

<figure><img src="image_6.png" /></figure>

B

<figure><img src="image_7.png" /><figcaption>**Fig. 3.** (A) Synthesis scheme of PU-[(Mo₂O₂S₂)ₙ(L)ₙ] polymers and (B) examples of PU-[(Mo₂O₂S₂)₂(L⁴)₂] polymer samples</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>**Fig. 4.** SEM images at (a) 10 µm scale, and zoomed at different levels: (b) × 5.000, (c) × 10.000, and (d) × 25.000. EDX dot maps for (e) Mo et (f) S, and (g) EDX spectrum of the PU-5%-[(Mo₂O₂S₂)₂(L⁶)₂] polymer.</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>**Figure 5.** Infrared spectrum of neat PU. Inset: zoomed-in section of the C=O band region.</figcaption></figure>

By disturbing the hydrogen bonding of the hard-segments and, to some extent, the soft-segments, the complexes lead to higher phase mixing.

Although infrared spectra provide information on hydrogen bonding in polymer matrices, they do not reveal whether the complexes are covalently bound to the polymers. In order to get further insight, the solubility of PU-complex polymers was studied.

## Solubility of PU-[(Mo₂O₂S₂)ₙ(L¹⁻⁶)ₙ] polymers in DMSO solvent

As the [(Mo₂O₂S₂)ₙ(L¹⁻⁶)ₙ] complexes are soluble in DMSO, pellets of all PU-[(Mo₂O₂S₂)ₙ(L¹⁻⁶)ₙ] composites have been introduced in this solvent at room temperature to evaluate the removal of complexes from the matrix. The neat PU is soluble in DMSO. After 48 h, the PU-[(Mo₂O₂S₂)(L¹)] and PU-1%-[(Mo₂O₂S₂)₂(L⁵)₂] polymers are completely solubilized with the formation of homogenous yellow solutions. The other polymers are giving also yellow solutions and colourless to pale yellow insoluble polymer solids (Table 1), suggesting total or partial removal of the complexes from the PU matrix and therefore those complexes are mainly not covalently bound in the PU matrices.

The ¹H NMR measurements were carried out only on 5% solutions by adding a few drops of DMSO-d⁶. In order to assign the peaks in obtained solutions, a deep NMR study of neat PU has first been performed. The proton assignments of neat PU (Figures 6 and 7, Figure S31, SI) have been performed based on ¹H-¹H COSY, ¹H-¹³C HSQC, ¹H-¹³C HMBC, and ¹H-¹⁵N HMBC methods (Figures S32-S36, SI). The d, e and f protons of hexyl group appear at 2.90, 1.35 and 1.20 ppm, respectively. The butyl fragment gives two peaks at 3.90 and 1.54 ppm corresponding to a and b protons, respectively. Concerning the PEG fragment, the g" and g' protons of ethylene fragment directly attached to carbamate linkage appear at 4.01 and 3.53 ppm respectively, while g protons from inside of the chain at 3.50 ppm. The polyurethane contains two types of carbamate linkage (i and i') with slightly different ¹H, ¹³C and ¹⁵N chemical shifts: 7.0 and 7.1, 157.5 and 157.4, and -296.6 and -296.3 ppm, respectively. Also, it was possible to establish the end groups of the polymer. Thus, a low intensity peak of carbon atom at 159.4 (i") ppm coupled with c" proton at 5.7 ppm can be assigned to the carbamate end group with slightly higher ¹H-¹⁵N coupling (-298.4 ppm). From ¹H-¹³C HMBC spectrum have been observed that h (4.60 ppm) proton is coupling with g"" (73.5 ppm) and g'" (61.4 ppm) carbons corresponding to the PEG end group.

The ¹H NMR spectra of soluble polymers and those giving colorless or pale-yellow solutions after DMSO treatment (Figure 8 and Figures S37-S40, SI) are displaying all peaks at the same positions as observed for neat PU and for the free coordination complexes including -NH₂ protons. However, one new low intensity multiplet at 8.46 ppm is also observed for PU-5%-[Mo₂O₂S₂(L¹)] (Fig. S8B, SI), which can be assigned to substituted thiourea group (R-NH(C=S)NH-R) and thus leading to the assumption that a small amount of [Mo₂O₂S₂(L¹)] complex is linked to polyurethane chains.

<figure><img src="image_10.png" /><figcaption>**Figure 6.** Schematic structure of polyurethane-PEG polymer and NMR assignments based on ¹H-¹H COSY, ¹H-¹³C HSQC, ¹H-¹³C HMBC, and ¹H-¹⁵N HMBC.</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>**Figure 7.** ¹H NMR spectrum of polyurethane-PEG polymer in DMSO-d₆.</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>**Fig. 8.** ¹H NMR spectra (DMSO-d₆) of polymers (●) neat PU compared to (A) (•) [(Mo₂O₂S₂)₂(L⁵)₂] complex and (•) DMSO-treated PU-5%-[(Mo₂O₂S₂)₂(L⁵)₂] polymer, and to (B) (•) [Mo₂O₂S₂(L¹)] complexe and (•) DMSO-treated PU-5%-[Mo₂O₂S₂(L¹)] polymer.</figcaption></figure>

<caption>**Table 1.** Results of the treatment of PU composites by DMSO at RT</caption>
<table><thead><tr><th>PU</th><th>After DMSO treatment</th></tr></thead><tbody><tr><td>PU</td><td>soluble</td></tr><tr><td>PU-1%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>1</sup>)]</td><td>soluble</td></tr><tr><td>PU-3%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>1</sup>)]</td><td>soluble</td></tr><tr><td>PU-5%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>1</sup>)]</td><td>soluble</td></tr><tr><td>PU-1%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>2</sup>)]</td><td>colourless gelatinous solid</td></tr><tr><td>PU-3%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>2</sup>)]</td><td>pale yellow solid</td></tr><tr><td>PU-5%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>2</sup>)]</td><td>pale yellow solid</td></tr><tr><td>PU-1%-[[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>3</sup>)<sub>2</sub>]</td><td>colourless solid</td></tr><tr><td>PU-1%-[[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>4</sup>)<sub>2</sub>]</td><td>colourless solid</td></tr><tr><td>PU-3%-[[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>4</sup>)<sub>2</sub>]</td><td>pale yellow solid</td></tr><tr><td>PU-5%-[[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>4</sup>)<sub>2</sub>]</td><td>pale yellow solid</td></tr><tr><td>PU-1%-[[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>5</sup>)<sub>2</sub>]</td><td>soluble</td></tr><tr><td>PU-3%-[[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>5</sup>)<sub>2</sub>]</td><td>pale yellow gelatinous solid</td></tr><tr><td>PU-5%-[[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>5</sup>)<sub>2</sub>]</td><td>yellow solid</td></tr><tr><td>PU-1%-[[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>6</sup>)<sub>2</sub>]</td><td>pale yellow solid</td></tr><tr><td>PU-3%-[[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>6</sup>)<sub>2</sub>]</td><td>pale yellow solid-gel</td></tr><tr><td>PU-5%-[[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>6</sup>)<sub>2</sub>]</td><td>pale yellow solid</td></tr></tbody></table>

Those results agree with infrared spectroscopy showing an increase amount of bound N-H groups in all PU-[(Mo₂O₂S₂)ₙ(L¹⁻⁶)ₙ] polymers. The colourless solid is indicative of higher embedding while the pale-yellow color of the DMSO treated polymers is suggesting that at low extent, the complexes can be chemically cross-linked into polymer and/or strongly embedded into polymer matrix. If the reactivity of the complexes is low, the available isocyanate groups can form with urethane linkages *allophanate* groups [ref] leading at some extent to the chemical cross-linking matrix which can also explain insoluble part of PU-[(Mo₂O₂S₂)ₙ(L¹⁻⁶)ₙ] polymers after DMSO treatment. The low reactivity of terminal amino groups of the complexes is due to the n-π conjugation. For [(Mo₂O₂S₂)₂(L⁵)₂] and [(Mo₂O₂S₂)₂(L⁶)₂] complexes, the phenol group might be inaccessible for polymerization reaction due to a steric hindrance.

## Swelling measurements

To shed light on the physical cross-linking of PU-[(Mo₂O₂S₂)ₙ(L¹⁻⁶)ₙ] polymers, the swelling measurements in toluene at room temperature were performed. Contrary to lower molecular mass polyurethane chains, the yellow [(Mo₂O₂S₂)ₙ(L¹⁻⁶)ₙ] complexes are not soluble in the toluene and they will not be removed from the polymers matrix. Thus, these measurements give the possibility to appreciate the contribution of the physical cross-linking. After 4 days of immersion in toluene, all polymer samples swelled to varying degrees. Toluene solutions after swelling were colourless, proving the lack of removal of complexes and/or lower polymer chains linked to complexes. The swelling degrees based on solvent uptake (SD<sub>SU</sub>), increase in polymer volume (SD<sub>IV</sub>) and the soluble fractions (F<sub>S</sub>) parameters were calculated using Eqs. (1)-(3) and reported in Table 2. Swelling degrees based on polymer volume (SD<sub>IV</sub>) increase compared with pure PU. The SD<sub>IV</sub> and SD<sub>SU</sub> values of pure PU and PU-[(Mo₂O₂S₂)(L¹)] are lower than for other polymers indicating a higher physical cross-linking. They also have similar DSC profile with high intensity T<sub>m</sub> peak. The SD<sub>IV</sub> and SD<sub>SU</sub> values for PU-[(Mo₂O₂S₂)(L²)] polymers are higher than those of PU-[(Mo₂O₂S₂)(L¹)] ones. This is due to the hydroxyl group in [(Mo₂O₂S₂)(L²)] complex leading to less ordered (1 and 3%) and almost amorphous (5%) PU-[(Mo₂O₂S₂)(L²)] structures. The almost amorphous PU-[(Mo₂O₂S₂)₂(L⁴)₂] polymers with tert-butyl group on phenyl ring show the highest SD<sub>IV</sub> and SD<sub>SU</sub> values which increases with concentration of the complexes (Table 2). This can be explained by the hydrophobic contribution of the tert-butyl group on polymer network swelling.

However, the lack of tert-butyl group in PU-1%-[(Mo₂O₂S₂)₂(L³)₂] polymer has the same SD<sub>IV</sub> and SD<sub>SU</sub> values than PU-1%-[(Mo₂O₂S₂)₂(L⁴)₂]. In contrast, the PU-1%-[(Mo₂O₂S₂)₂(L⁵)₂] polymer obtained from rectangular complex containing two phenol groups show close polymer structure as the parent PU and thus, the same SD<sub>IV</sub>/SD<sub>SU</sub> values and DSC profile. Increasing the concentration of the complex leads to different ordered PU-3%-[(Mo₂O₂S₂)₂(L⁵)₂] and PU-5%-[(Mo₂O₂S₂)₂(L⁵)₂] polymers with higher SD<sub>IV</sub>/SD<sub>SU</sub> values. Compared to PU-[(Mo₂O₂S₂)₂(L⁵)₂] polymers, the PU-[(Mo₂O₂S₂)₂(L⁶)₂] ones have additionally two methyl groups. Increasing the hydrophobic component gives rise to less ordered polymers and to an increase in SD<sub>IV</sub> and SD<sub>SU</sub> values. The values of the soluble fractions (F<sub>S</sub>) (Table 2) correspond to the unbound polymer chains in the polymer network. The lower F<sub>S</sub> values suggest higher extent of polymerization reaction.

At this stage, we can conclude that all PU-[(Mo₂O₂S₂)ₙ(L¹⁻⁶)ₙ] polymers contain to varying degrees [(Mo₂O₂S₂)ₙ(L¹⁻⁶)ₙ] complexes embedded into the polymer matrix through intermolecular hydrogen bond networks (physical cross-linking), as depicted in Fig. 9.

<figure><img src="image_13.png" /><figcaption>**Fig. 9.** Hydrogen bonding between complexes and polyurethane matrix: (A) (NH...O-ether), (B) Mo=O...NH-C=O, and (C) (NH...O=C-NH).</figcaption></figure>

**Table 2.** The increase in polymer volume (SD<sub>IV</sub>), solvent uptake (SD<sub>SU</sub>) and soluble fractions (F<sub>S</sub>) calculated from swelling
<table><caption>**Table 3.** The T<sub>onset</sub> and T<sub>end</sub> temperatures from TGA measurements.</caption><thead><tr><th>PU</th><th>T<sub>onset</sub></th><th>T<sub>end</sub></th></tr></thead><tbody><tr><td>PU</td><td>180</td><td>510</td></tr><tr><td>PU-1%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>1</sup>)]</td><td>210</td><td>533</td></tr><tr><td>PU-3%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>1</sup>)]</td><td>222</td><td>525</td></tr><tr><td>PU-5%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>1</sup>)]</td><td>232</td><td>531</td></tr><tr><td>PU-1%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>2</sup>)]</td><td>231</td><td>537</td></tr><tr><td>PU-3%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>2</sup>)]</td><td>209</td><td>532</td></tr><tr><td>PU-5%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>2</sup>)]</td><td>213</td><td>523</td></tr><tr><td>PU-1%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>3</sup>)<sub>2</sub>]</td><td>226</td><td>547</td></tr><tr><td>PU-1%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>4</sup>)<sub>2</sub>]</td><td>222</td><td>549</td></tr><tr><td>PU-3%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>4</sup>)<sub>2</sub>]</td><td>220</td><td>553</td></tr><tr><td>PU-5%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>4</sup>)<sub>2</sub>]</td><td>222</td><td>556</td></tr><tr><td>PU-1%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>5</sup>)<sub>2</sub>]</td><td>209</td><td>540</td></tr><tr><td>PU-3%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>5</sup>)<sub>2</sub>]</td><td>213</td><td>546</td></tr><tr><td>PU-5%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>5</sup>)<sub>2</sub>]</td><td>214</td><td>533</td></tr><tr><td>PU-1%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>6</sup>)<sub>2</sub>]</td><td>217</td><td>538</td></tr><tr><td>PU-3%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>6</sup>)<sub>2</sub>]</td><td>212</td><td>538</td></tr><tr><td>PU-5%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>6</sup>)<sub>2</sub>]</td><td>219</td><td>554</td></tr></tbody></table>

<figure><img src="image_14.png" /><figcaption>**Figure 10.** TGA curves of PU, PU-1%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>1</sup>)], PU-3%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>1</sup>)] and PU-5%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>1</sup>)] polymers</figcaption></figure>

## TGA analysis

The TGA analysis has been performed from 25 to 700°C under oxygen flow. The TGA thermograms of PU-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>1</sup>)] polymers are depicted in Figure 10, while for the other polyurethanes they are given in SI (Figures S41-S45). The initial degradation temperature (T<sub>onset</sub>) and the temperature at which maximum weight loss takes place (T<sub>end</sub>) are shown in Table 3. Neat PU show three oxidative thermal degradation steps: 180-316, 316-392 and 392-510°C. The degradation occurring until 392°C corresponds to radical scission of hard segments urethane linkages [25] while further degradation up to 510°C is assessed to the soft segments [25]. As it was observed for similar polyurethanes, the degradation products of hard segments are the hexamethylene diisocyanate and 1,4-butadiol [27]. Further degradation of soft segments implies PEG scission to different lower molecular weight compounds as ethers, ether-alcohols and ether-alkenes [27]. The PU-[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>n</sub>(L<sup>1-6</sup>)<sub>n</sub>] polymers with embedded complexes show mostly two degradation steps shifted to higher temperatures: 209-400 and 400-556 °C. The small residual weight at T<sub>end</sub> corresponds roughly to the molybdenum(VI) oxide MoO<sub>3</sub> obtained by oxidative degradation of Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub><sup>2+</sup> clusters and the removal of sulfur as SO<sub>2</sub>. The PU-[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>n</sub>(L<sup>1-6</sup>)<sub>n</sub>] polymers show relatively enhanced thermal stability, which can be explained by cumulative effect of several factors: i) the metal ions delay the action of heat source on the hard segments, and thus the formation of free radicals resulting from urethane decomposition [28]; ii) the intermolecular hydrogen bonds between [(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>n</sub>(L<sup>1-6</sup>)<sub>n</sub>] complexes and hard/soft segments increase the thermal stability of polymer matrix also retarding the action of free radicals [28]; and iii) the “barrier effect” of [(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>n</sub>(L<sup>1-6</sup>)<sub>n</sub>]-based matrix, which delays the release of volatile degradation products from the polymer and thus overall decomposition [29].

## DSC analysis

DSC measurements for all polyurethanes were performed in the range -85 to +150°C under nitrogen atmosphere giving superimposable thermograms after the first heating. The DSC thermograms for PU-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>1</sup>)], PU-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>2</sup>)], PU-[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>4</sup>)<sub>2</sub>] and PU-[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>5</sup>)<sub>2</sub>] polymers are given in the Figure 11. The embedding of the complexes into polymer matrix through hydrogen bonding leads to different ordered structures and thus different physical states.

The phase transition temperatures are listed in the Table 4. The neat PU (Figure 11) shows a glass transition temperature (T<sub>g</sub>) at -49.9 °C, characteristic for the aliphatic polyurethanes [25]. This temperature corresponds, on the heating mode, to the phase transition from lower to higher polymer chain mobility of soft segment domains. Two endothermic peaks at 16.8 and 91.2 °C are the melting temperatures corresponding to the dissociation of urethane soft segments (T<sub>m SS</sub>) and hard segments (T<sub>m HS</sub>) hydrogen bonding,
respectively [ref]. The higher intensity of the first endothermic peak ($T_m$ SS) is suggesting the high content of urethane soft segments hydrogen bonding established between soft and hard segments, and thus a well phase mixing of soft and hard domains. This homogenous mixing in the polymer matrix is also confirmed by the single $T_g$ transition [30]. Compared to neat PU, PU-[(Mo₂O₂S₂)ₙ(L¹⁻⁶)ₙ] polymers show DSC thermograms with different profiles depending on the type and concentration of [(Mo₂O₂S₂)ₙ(L¹⁻⁶)ₙ] complexes.

The common feature for all samples is the $T_g$ shift to higher temperatures when the concentration of [(Mo₂O₂S₂)ₙ(L¹⁻⁶)ₙ] complexes is increased. This can be explained by the increased hydrogen bonding between the [(Mo₂O₂S₂)ₙ(L¹⁻⁶)ₙ] complexes and the polymer matrix, which restricts chain mobility in the soft segments (Figure 11).

All PU-[Mo₂O₂S₂(L²)] polymers (Figure 11A) show the same features as neat PU. The crystallinity of soft domains slightly decreases (from 16.8 for neat PU to 11.8 for PU-5%) as the amount of complex increases. The same trend is observed for the melting point of hard domains, decreasing from 91 to 84 °C, as the cluster content increases.

For PU-[Mo₂O₂S₂(L²)] polymers show different DSC behaviour than those described above (Figure 11B). The melting temperature of hard domains is only observable for 1% of complex content at 17.1 °C, comparable to neat PU. This polymer also shows a crystallization just before the melting at around -1 °C. In this case the addition of the [Mo₂O₂S₂(L²)] complex gives rise to more amorphous polymers. The hard segments give a sharp endotherm with two peaks at 65.7 and 97.2 °C, corresponding to short- and long-range order, respectively. At 3% complex content, soft segments $T_c$ is shifted to a higher temperature (7.5 °C), while soft segment melting endotherm $T_m$ disappears, corresponding to the formation of a stable, ordered soft segment structure. The melting endotherm temperatures of hard segments are slightly shifted to lower temperatures. Further increase of complex content to 5% leads to almost amorphous polymer with very low intensity of short-range hard segments order (69.8 °C). Compared to [Mo₂O₂S₂(L¹)] complex, the [Mo₂O₂S₂(L²)] one contains additional hydroxyl groups which can act as terminal blocking monomers and/or cross linkers and thus leading to different ordered structure.

tert-butyl groups on aromatic rings give almost amorphous polymers. The 1% polymers show two $T_g$ transitions at -44°C (soft segments) and 40.6 °C (hard segments). For 3 and 5% only one $T_g$ transition is observed at -37.60 and -38.68 °C, respectively.

For [(Mo₂O₂S₂)₂(L⁵)₂] polymers, which has two phenol groups and no tert-butyl groups, the DSC behaviour changes (Figure 11D). Thus, at 1% complex content, it exhibits an unstable soft segment crystallization process ($T_c$ soft segments = -16.5 °C) followed by a melting endotherm peak at 13.8 °C. The hard segments melting endotherms are observed at higher temperatures ($T_m$ hard segments = 89.8 and 107.2 °C). At 3% and 5%, the soft segments crystallization process becomes stable and is shifted gradually to higher temperatures, 5.3 and 16.7 °C, respectively. In contrast, the melting hard segments peaks are downward shifted consistent with lower ordered hard segments compared to 1%, but not lower than neat PU. This gradual increase of $T_c$ values is suggesting an increase in freedom of soft segment chains, also confirmed by the lower $T_g$ values than in PU-[(Mo₂O₂S₂)₂(L⁴)₂] polymers. Thus, the lack of tert-butyl groups and the presence of phenol groups lead at some extent to more ordered polymer structure.

The retention of phenolic groups in [(Mo₂O₂S₂)₂(L⁶)₂] complex and the addition of methyl group in p-position lead to the mixed DSC behaviour of the polymer (Figure S47, SI). At 1% complex content, the PU-1%-[(Mo₂O₂S₂)₂(L⁶)₂] polymer shows similar DSC thermogram as PU-3%-[(Mo₂O₂S₂)₂(L⁵)₂] one. At 3%, the polymer is less crystalline. Further increase at 5% is giving amorphous polymer. This result shows that the methyl group, to a lesser extent than the tert-butyl group, reduces soft segment mobility and polymer crystallinity.

The thermogram of PU-1%-[(Mo₂O₂S₂)₂(L³)₂] (Figure S46, SI) obtained from the [(Mo₂O₂S₂)₂(L³)₂] complex with no phenol and alkyl groups, is similar to that of PU-5%-[(Mo₂O₂S₂)₂(L⁵)₂] polymer ($T_g$ soft segments = -40.6 °C; $T_c$ soft segments = 16.7 °C) (Figure 11D), showing transitions at roughly the same temperatures ($T_g$ soft segments = -42.7 °C; $T_c$ soft segments = 20 °C).

<table><caption>**Table 4.** The phase transitions temperatures (°C), heat capacity, Cp (J/g×°C) and change of enthalpy, ΔH (J/g) for Mo-based polyurethanes.</caption><thead><tr><th>PU</th><th>T<sub>g</sub> ss (Cp)</th><th>T<sub>g</sub> HS (Cp)</th><th>T<sub>c</sub>ss (H)</th><th>T<sub>m</sub> ss (H)</th><th>T<sub>m</sub> HS (H)</th></tr></thead><tbody><tr><td>PU</td><td>-49.9 (0.3)</td><td></td><td></td><td>16.8 (16.8)</td><td>91.2 (2.1)</td></tr><tr><td>PU-1%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>1</sup>)]</td><td>-46.2 (0.4)</td><td></td><td></td><td>14.9 (26.3)</td><td>67.9 and 84.8 (10.2)</td></tr><tr><td>PU-3%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>1</sup>)]</td><td>-44.3 (0.4)</td><td></td><td></td><td>15.4 (28.3)</td><td>86.3 and 107.5 (6.7)</td></tr><tr><td>PU-5%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>1</sup>)]</td><td>-45.7 (0.4)</td><td></td><td>-15.8 (4.6)</td><td>11.8 (17.3)</td><td>83.8 and 102.8 (10.8)</td></tr><tr><td>PU-1%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>2</sup>)]</td><td>-45.5 (0.8)</td><td></td><td>-1.0 (6.3)</td><td>17.1 (11.4)</td><td>65.7 and 97.2 (17.7)</td></tr><tr><td>PU-3%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>2</sup>)]</td><td>-43.2 (0.8)</td><td></td><td>7.5 (11.1)</td><td></td><td>64.8 and 94.9 (12.8)</td></tr><tr><td>PU-5%-[Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>2</sup>)]</td><td>-38.9 (0.8)</td><td></td><td></td><td></td><td>69.8 (0.4)</td></tr><tr><td>PU-1%-[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>3</sup>)<sub>2</sub>]</td><td>-42.7 (0.8)</td><td></td><td>19.9 (10.2)</td><td></td><td></td></tr><tr><td>PU-1%-[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>4</sup>)<sub>2</sub>]</td><td>-43.9 (0.8)</td><td>40.6 (0.4)</td><td></td><td></td><td>101.2 (0.4)</td></tr><tr><td>PU-3%-[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>4</sup>)<sub>2</sub>]</td><td>-37.6 (0.7)</td><td></td><td></td><td></td><td>114.4 (2.4)</td></tr><tr><td>PU-5%-[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>4</sup>)<sub>2</sub>]</td><td>-38.6 (0.7)</td><td></td><td></td><td></td><td>107.8 (0.6)</td></tr><tr><td>PU-1%-[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>5</sup>)<sub>2</sub>]</td><td>-47.8 (0.4)</td><td></td><td>-16.5 (3.2)</td><td>13.8 (20.7)</td><td>89.8 and 107.2 (15.2)</td></tr><tr><td>PU-3%-[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>5</sup>)<sub>2</sub>]</td><td>-43.2 (0.8)</td><td></td><td>5.3 (0.xx)</td><td></td><td>68.3 and 97.1 (0.xx)</td></tr><tr><td>PU-5%-[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>5</sup>)<sub>2</sub>]</td><td>-40.6 (0.8)</td><td></td><td>16.7 (11.1)</td><td></td><td>69.7 and 94.1 (8.3)</td></tr><tr><td>PU-1%-[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>6</sup>)<sub>2</sub>]</td><td>-44.5 (0.8)</td><td></td><td>2.5 (5.2)</td><td></td><td>66.3 and 96.5 (18.7)</td></tr><tr><td>PU-3%-[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>6</sup>)<sub>2</sub>]</td><td>-43.9 (0.8)</td><td></td><td></td><td>13.8 (1.9)</td><td>64.3 and 97.6 (10.9)</td></tr><tr><td>PU-5%-[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>6</sup>)<sub>2</sub>]</td><td>-39.1 (0.8)</td><td></td><td></td><td></td><td></td></tr></tbody></table>

The PU-[(Mo₂O₂S₂)₂(L⁴)₂] polymers (Figure 11C) having
<figure><img src="image_15.png" /><figcaption>**Fig. 11.** DSC thermograms on heating (°C) for PU and PU-[Mo₂O₂S₂(L¹)] (A), PU-[Mo₂O₂S₂(L²)] (B), PU-[(Mo₂O₂S₂)₂(L⁴)] (C), and (D) PU-[(Mo₂O₂S₂)₂(L⁵)] (D) polymers in 1% (•), 3% (•) and 5% (•) complex content and compared to parent polyurethane (•).</figcaption></figure>
## 4. Conclusions

In this study, 16 [Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>]<sup>2+</sup>-based polyurethanes (PU-[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>n</sub>(L<sup>1-6</sup>)<sub>n</sub>] (n = 1, 2)) have been successfully obtained and characterized. Furthermore, four new coordination complexes [Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>2</sup>)], [(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>3</sup>)<sub>2</sub>], [(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>5</sup>)<sub>2</sub>] and [(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>2</sub>(L<sup>9</sup>)<sub>2</sub>] have been obtained and, excepting [Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>(L<sup>2</sup>)], characterized by single-crystal X-ray diffraction. Overall the [(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>n</sub>(L<sup>1-6</sup>)<sub>n</sub>] complexes are mostly embedded into polymer matrix without covalent bonds but involving H-bond networks, as were confirmed by Swelling-NMR measurements. Depending on the nature of the complex and the content, the DSC analyses show different ordered polymer structures which are set on hydrogen bonding network and hydrophobic interactions of embedded complexes into polymer matrix. The homogenous distribution of the [(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>n</sub>(L<sup>1-6</sup>)<sub>n</sub> in the polymers was confirmed by SEM/EDX analysis. All PU-[(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>n</sub>(L<sup>1-6</sup>)<sub>n</sub>] polymers show enhanced thermal stability compared to neat PU. Even though [(Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>)<sub>n</sub>(L<sup>1-6</sup>)<sub>n</sub>] complexes do not display significant biological properties, this strategy can be extended to other polyurethanes embedding bioactive [Mo<sub>2</sub>O<sub>2</sub>S<sub>2</sub>]<sup>2+</sup> complexes which are currently under investigation in our laboratory.

### CRediT authorship contribution statement

**Sergiu Calancea:** Synthesis, characterization, supervision and Writing - original draft. **Diana Cebotari:** Synthesis and characterization of complexes and composites. **Roa AlChamandi:** Synthesis of composites and TGA measurements. **Yann Molard:** DSC characterization, review & editing. **Maria Amelia-Cortes:** DSC characterization, writing, review & editing. **Carine Livage:** SEM/EDX characterization. **Mohamed Haouas:** NMR characterization, review & editing. **Jérôme Marrot:** X-ray diffraction characterization. **Aurelian Gulea:** review & editing. **Cyril Gorny:** sxelling characterization. **Bruno Fayolle:** swelling characterization, review & editing. **Sébastien Floquet:** Funding acquisition, supervision, writing - review & editing.

### Declaration of competing interest

The authors have no competing financial interests concerning the work reported in this article.

### Data availability

Data will be made available on request.

### Acknowledgements

University of Versailles, the CNRS, and the French National Research Agency (ANR) as part of the "Investissements d'Avenir" program, CHARMMAT ANR-11-LABX-0039, are gratefully acknowledged for financial support. DC gratefully acknowledges Campus France for Excellence Eiffel grant as well as State University of Moldova for funding her PhD thesis. This work is also supported by the "ADI 2019" project funded by the IDEX Paris-Saclay, ANR-11-IDEX-0003-02, "a Joint research projects AUF-MECR 2020-2021" funding program. The financial support from National Agency for Research and Development (ANCD) of the Republic of Moldova (Project No 20.80009.5007.10) is also acknowledged. The authors thank **Vincent Guérineau**, for MALDI-TOF measurements and also Ms **Mahdia Mouhamed**, Ms **Doha El Hadfi**, ans **Mr Alexis Leblais**, undergraduate students, for their contribution to the experimental work.

### Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi...

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