Controlling the Self‐Assembly of a Mixed‐Metal Mo/V–Selenite Family of Polyoxometalates

Abstract

Five mixed-metal mixed-valence Mo/V polyoxoanions, templated by the pyramidal SeO(3)(2-) heteroanion have been isolated: K(10)[Mo(VI)(12)V(V)(10)O(58)(SeO(3))(8)]⋅18 H(2)O (1), K(7)[Mo(VI)(11)V(V)(5)V(IV)(2)O(52)(SeO(3))]⋅31 H(2)O (2), (NH(4))(7)K(3)[Mo(VI)(11)V(V)(5)V(IV)(2)O(52)(SeO(3))(Mo(V)(6)V(V)-O(22))]⋅40 H(2)O (3), (NH(4))(19)K(3)[Mo(VI)(20)V(V)(12)V(IV)(4)O(99)(SeO(3))(10)]⋅36 H(2)O (4) and [Na(3)(H(2)O)(5){Mo(18-x)V(x)O(52)(SeO(3))} {Mo(9-y)V(y)O(24)(SeO(3))(4)}] (5). All five compounds were characterised by single-crystal X-ray structure analysis, TGA, UV/Vis and FT-IR spectroscopy, redox titrations, and elemental and flame atomic absorption spectroscopy (FAAS) analysis. X-ray studies revealed two novel coordination modes for the selenite anion in compounds 1 and 4 showing η,μ and μ,μ coordination motifs. Compounds 1 and 2 were characterised in solution by using high-resolution ESI-MS. The ESI-MS spectra of these compounds revealed characteristic patterns showing distribution envelopes corresponding to 2- and 3- anionic charge states. Also, the isolation of these compounds shows that it may be possible to direct the self-assembly process of the mixed-metal systems by controlling the interplay between the cation "shrink-wrapping" effect, the non-conventional geometry of the selenite anion and fine adjustment of the experimental variables. Also a detailed IR spectroscopic analysis unveiled a simple way to identify the type of coordination mode of the selenite anions present in POM-based architectures.