Abstract
We report the syntheses and characterizations of the first polyoxothiometalate complexes isolated from the reaction of the oxothiocationic [(Mo2O2S2)-O-V](2+) precursor and bisphosphonate ligands H2O3PCR(OH)-PO3H2 (R = C4H5N2, zoledronic acid; R = C3H6NH2, alendronic acid). [(Mo2O2S2(H2O))(4)(O3PC(O)-(C4H6N2)PO3)(4)](8-) (Mo8S8(Zol)(4)) and [(Mo2O2S2(H2O))(4)(O3PC(O)(C3H6NH3)PO3)(4)](8-)(Mo8S8(Ale)(4)) contain four Mo-V dimers connected via bisphosphonate ligands. These compounds offer a unique opportunity to compare the structures and properties of cyclic compounds obtained with [Mo2O2S2](2+) and with [Mo2O4](2+). The oxothio compounds appear less stable in solution than the oxo analogue, confirming the higher lability and versatility of [Mo2O2S2]-based compounds compared to [Mo2O4]-based POMs. Multinuclear and multidimensional solid-state NMR studies were carried out to complement X-ray diffraction analysis. Information on short-range interactions, dynamic behaviors, and local disorder within the crystalline materials are therefore reported. Furthermore, the electrocatalytic properties of Mo8S8(Ale)(4) and of the analogous [(Mo2O4(H2O))(4)(O3PC(O)(C(3)H6NH(3))PO3)(4)](8-) (Mo8O8(Ale)(4)) immobilized onto the surface of a glassy carbon electrode were studied, thus evidencing the ability of [Mo2O2S2]-based cycles to promote the reduction of protons into hydrogen, whereas the oxo analogue appeared inactive.