A Decade of Oxothiomolybdenum Wheels: Synthesis, Behavior in Solution, and Electrocatalytic Properties

Abstract

The last decade has see the development of sulfur‐containing polyoxometalates (POTMs) as a subclass of the polyoxometalate family. The structural and physico‐chemical properties of this emerging class of compounds is dominating by the striking coordination properties of the [Mo2O2S2(OH2)6]2+ oxothio cation, used as a building block. The cyclic topology of this arrangement corresponds to the main feature of the {Mo2O2S2}‐based compounds, able to develop cycle‐based chemistry. The control of the linear oligomerization of the {Mo2O2S2} core is achieved by the presence of the anionic component, which acts as a template. Here, we report on recent examples which illustrate how the use of various template ions such as halide, sulfate, polyphosphate, and polycarboxylate anions allows to tune the nuclearity of the inorganic host from {Mo8} to {Mo18}. A special focus on behavior in solution is given, highlighting the dynamic and fluxional character of these host–guest systems. The Diffusion Ordered Spectroscopy (DOSY) 1H NMR, carried out on a large series of cycle‐based and capsule‐like compounds, demonstrates that such a method can be applied for the speciation of POM anions in solution. Finally, electrocatalytic behavior of the {Mo2O2S2}‐based compounds is presented. Preliminary results show that the electrocatalytic reduction of protons into hydrogen (HER) could constitute one of the most relevant applications for this class of molecular compounds.

Tunable Keplerate Type‐Cluster “Mo132” Cavity with Dicarboxylate Anions

“…For carbon atoms of the carboxylate functions, two peaks are observed in agreement with coordinated and uncoordinated carboxylate groups. As a general behavior, the encapsulation of ligands within cycles or capsules usually leads to a low‐frequency shift and a broadening of the NMR signals,28 while the coordination of ligand to metallic centers produces an opposite effect, featured by a deshielding at the involved nuclei 29. For both compounds NH 4 ‐3 and NH 4 ‐4 , one carboxylate function is deshielded of about Δ δ ∼ +1 ppm while the second appears significantly shielded Δ δ ∼−5 ppm.…”

A building block strategy to access sulfur-functionalized polyoxometalate based systems using {Mo2S2O2} and {Mo3S4} as constitutional units, linkers or templates

“…Such an arrangement is similar to those observed in oxothiomolybdic rings, resulting from the cyclic condensation of the {Mo 2 O 2 S 2 } building block. 36 The 31 P and 183 W NMR spectra of the tetra-Dawson thio derivative exhibit the resonances expected for a C 2h idealized symmetry Cation-directed synthesis and conformational change with [A-a-AsW 9 O 33 ] 9À . We previously reported how a simple inorganic system based on the chemical complementarities between the common trivacant ligand [B-a-AsW 9 O 33 ] 9À (polyoxometalate unit, denoted POM or {AsW 9 O 33 }) and the ditopic cation [Mo 2 O 2 S 2 ] 2+ (linker unit, denoted L or {Mo 2 }) can produce relevant modular assemblies, stereochemically oriented and conformationally ordered through weak supramolecular interactions.…”

“…The central {M VI O 6 } octahedron exhibits a linear OQM-OH 2 axis, and the presence of two protonated oxygen atoms in the {M VI O 4 } equatorial plane. This example deriving rather from the templated-oxothiomolybdic ring, widely investigated by our group,29,36 corresponds to the simplest possible combination, but it could be anticipated that oxothiomolybdic cyclic systems should be able to stabilize and trap transient polyoxometalates.The change of the synthetic conditions such as the sequence of addition of the reagents, the use of acetic buffer and the increase of the [M VI O 4 ] 2À /[M 2 O 2 S 2 (H 2 O) 6 } 2+ ratio allowed isolation of the first high nuclearity polyoxothiomolybdate ion 62. …”

Syntheses, characterizations and properties of [Mo2O2S2]-based oxothiomolybdenum wheels incorporating bisphosphonate ligands

“…For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c2dt30534h cyclic arrangements through direct connections of [Mo 2 O 2 S 2 ]units via hydroxo bridges. Such a spontaneous cyclization process, mainly entropically driven, has allowed the development of relevant host-guest chemistry using various organic ligands as template agents 21,35. In the present contribution, the NH 2 (alendronic acid, noted Ale) was investigated.…”