Construction of a new binding manner in carboxylic acid-functionalized phosphomolybdates

A new binding manner of C–N–Mo bonds was constructed in carboxylic acid-functionalized phosphomolybdates, and the polyanion was present as a hexamer.

A [Mo2O2S2]-based ring system incorporating tartrate as the bridging ligand: synthesis, structure and catalytic activity of Cs4[Mo2O2(μ-S)2]2(μ4-tart)2 (tart=[C4H2O6]4−)

Treatment of [Mo2S2O2(H2O)6]2+ with racemic tartaric acid (tartH4) in the presence of sodium hydroxide and cesium chloride in aqueous solution led to the isolation of a new tetra-molybdenum ring cluster Cs4[Mo2O2(μ-S)2]2(μ4-tart)2. The cyclic cluster polyanion consists of two dinuclear [Mo2O2(μ-S)2]2+ moieties and two bridging tart4− ligands. The cyclic polyoxothiomolybdate cluster, supported on the mesoporous silica SBA-15, was tested for heterogenerous catalysis in thiophene hydrodesulfurization.

Controlled assembly of hybrid architectures based on carboxylic acid ligands and [(O3PCH2PO3)Mo6O22]12−

Polyanion 2a with a reverse symmetrical “crown-type” structure is composed of two {(HO₃PCH₂PO₃)Mo₆O₁₈(CH₃CO₂)₂} subunits and a linking bridge.

Self assembly of carboxylate/alcoholate functionalized ring-shape phosphomolybdates

Carboxylate and alcoholate ligands were covalently attached to a [HPMo₆O₂₁]²⁻ cluster to generate a series of inorganic–organic hybrid phosphomolybdates.

Controlled assembly of inorganic-organic frameworks based on [SeMo6O21]4- polyanion

The chemical system based on [SeMo6O21](4-) polyanion and carboxylate ligand has been investigated. According to the inherent nature of organic groups, a series of selenomolybdates with three architectures have been isolated through rational and deliberate synthetic routes by stereospecific addition of different carboxylic acids. Such an approach is potentially interesting for {SeMo6} cluster, which exhibits a high surface nucleophilicity and is capable of being functionalized by covalently bound carboxylic acids. Investigation of the assemblies reveals that carboxylic acids have good flexibility and conformational freedom, representing the powerful chemical tools to control the polyanion assembly processes.

Tuning the electrocatalytic hydrogen evolution reaction promoted by [Mo2O2S2]-based molybdenum cycles in aqueous medium

We report the syntheses and characterizations, in the solid state and in solution, of three new cyclic polyoxothiomolybdates self-assembled around 2,5-dimethylterephthalate (DMT) and 2,5-bis(trifluoromethyl)terephthalate (DFMT) ligands, namely [Mo12DMT](2-), [Mo12DFMT](2-) and [Mo16DFMT](2-). A series of these two Mo12-compounds completed by the two Mo12-compounds obtained with 2,3,5,6-tetramethylterephthalate and trimesate ligands offer the opportunity to compare their electro-catalytic properties for reduction of protons into hydrogen. The ability of these compounds to promote the reduction of protons into hydrogen in aqueous medium is evidenced and the influence of the embedded ligand is highlighted, thus allowing proposal of a mechanism for the hydrogen evolution reaction catalyzed by these clusters.

Structure, properties and reactivity of polyoxometalates: a theoretical perspective

In the thematic review dedicated to polyoxometalate (POM) chemistry published in Chemical Reviews in 1998, no contribution was devoted to theory. This is not surprising because computational modelling of molecular metal-oxide clusters was in its infancy at that time. Nowadays, the situation has completely changed and modern computational methods have been successfully applied to study the structure, electronic properties, spectroscopy and reactivity of POM clusters. Indeed, the progress achieved during the past decade has been spectacular and herein we critically review the most important papers to provide the reader with an almost complete perspective of the field.

Dynamic properties of a hexadecamolybdenum wheel: studies in solution and density functional theory calculations

Variable temperature (1)H NMR studies of the host-guest complex [Mo(16)O(16)S(16)(OH)(16)(H(2)O)(4)(PDA)(2)](4-) (1 ; PDA(2-) = phenylenediacetate) previously carried out in D(2)O have revealed a complex behavior in solution, involving a gliding motion of both parallel phenyl rings of the PDA(2-) ligands. In the present work, we present new NMR spectra carried out in the aprotic solvent CD(3)CN, which allow the observation of the proton signals associated with the bridging hydroxo groups of the inorganic host. The new spectra provide detailed information about the concerted reorganization of the guest components, that is, PDA(2-) and water molecules. The existence of an equilibrium between two distinct isomers differing in the linking mode between the inorganic host and the two equivalent PDA(2-) ligands is evidenced. This equilibrium appears strongly dependent upon the temperature, leading to a complete inversion of the distribution between 300 and 226 K. The thermodynamic data related to the isomerization reaction have been determined (Delta(r)H = -50.5 kJ mol(-1) and Delta(r)S = -215 J mol(-1) K(-1)). Furthermore, at low temperature, one of the isomers exists in two conformations, only differing in the H-bond network involving the inner water molecules. Density functional theory calculations were carried out to push ahead the interpretations obtained from experiment, identify the isomers of 1, and specify the role and the positions of the guest water molecules. Among the various structures that have been calculated for 1, three fall in a narrow energy range and should correspond to the species characterized by variable-temperature (1)H NMR experiments in CD(3)CN. Finally, this study shows how the internal disposition of the ligands affects the ellipticity of the Mo(16) ring which varies from one isomer to the other in the 0.73-1 range and highlights solvation of the ring as one of the key parameters for the conformational design of these flexible host-guest systems.