New structures based on the mixed valence polyoxometalate cluster [V12B18O60H6]n−

Abstract

Hydrothermal synthesis was used to obtain four new crystalline lattices derived from the functionalization of the [V₁₂B₁₈O₆₀H₆]ⁿ⁻ cluster: Na₈(H₃O){[Ni(H₂O)₅][V₁₂B₁₈O₆₀H₆]}·12.5H₂O (1), Na₅ (H₃O)₄{[Ni (H₂O)₃(en)][V₁₂B₁₈O₆₀H₆]}·9H₂O (2), and Na₉(H₃O){Zn_0.5[V₁₂B₁₈O₆₀H₆]}·11H₂O (3), [Hen][H₂en]{[Zn(en)₂]₃ [V₁₂B₁₈O₆₀H₆]}·3H₂O (4). All four compounds crystallize in the space group C2/c. Compounds (1) (2) and (4) are 0D species, while for (3) there is some degree of covalent connectivity between the anionic units, due to the presence of Zn^II cations with partial occupation between them. On the basis of structural data and BVS calculations, these functionalized cluster species present mixed-valence ratios of 11V^IV/1V^V for (1), (2) and (3) and 9V^IV/3V^V for compound (4). Compounds (1), (2) and (3) present sodium and hydronium ions in the crystalline lattice, while protonated ethylenediamine is observed in compound (4). These cations balance the negative charge of the corresponding clusters and stabilize the crystalline lattice by electrostatic interactions. In the studied compounds, Ni^II ions coordinate to the vanadyl oxygen atoms, whereas the Zn^II cations coordinate both to the vanadyl oxygen atoms and to the oxygen atoms bonded to boron centres. The electronic spectra in the low energy range are dominated by the IVCT phenomenon, since the functionalization of the cluster [V₁₂B₁₈O₆₀H₆]ⁿ⁻ by different transition metal ions does not affect the observed absorption bands.