Tetrabutylammonium Salts of [Mo₁₂O₂₈(μ-L)₈]^4– Polyoxometal Clusters with Pyrazolate and Triazolate Ligands

The metathesis of ammonium cations in (NH₄)₄[Mo₁₂O₂₈(μ-L)₈] (L = pz (pyrazolate) and trz (1,2,4-triazolate)) with tetrabutylammonium is performed under boiling in an aqueous solution with Bu₄NOH. The substitution of cations and the preservation of the anionic cluster fragment are confirmed by a number of physicochemical methods such as XRD, ¹H NMR, and mass spectrometry. The resulting compounds are soluble and stable in organic solvents, so their redox properties are studied. According to the cyclic voltammetry data, the compounds exhibit reversible oxidation with E_1/2 = 0.26 V and 0.61 V for L = pz and trz respectively. The electronic structure is studied by quantum chemical calculations. It is shown that the frontier molecular orbitals of these compounds are mainly composed of molybdenum d-orbitals.