Synthesis and characterization of fluoride-incorporated polyoxovanadates

•The distribution of oxovanadates with halide in the mixed solvent system was established.•Fluoride anions have a significant effect on the distribution of oxovanadates.•Fluoride-incorporated polyoxovanadates were characterized by X-ray and 51VNMR analyses.•A heptavanadate possesses both tetrahedrally and square-pyramidally coordinated vanadium atoms.

The speciation studies of oxovanadates are essential to clarify their biological activities. We surveyed the distribution of oxovanadate species in the presence of halide anions with various acid concentrations in an aqueous mixed-solvent system. The presence of chloride, bromide, and iodide anions has no effects on the appearance of polyoxovanadate species observed in 51V NMR. Those are the precedent formation of metavanadate species and decavanadates. The presence of fluoride anion during the addition of acids exhibits strong intervention in the polyoxovanadate equilibria and we found the subsequent formation of two polyoxovanadate species by 51V NMR observation. From the estimated experimental condition, we isolated fluoride-incorporated polyoxovanadates {Et4N}4[V7O19F] and {Et4N}4[HV11O29F2], successfully. Polyanion [V7O19F]4 − is the fluoride-incorporated all V(V) state polyoxovanadate which has two different coordination environments of tetrahedral and square pyramidal vanadium units within the one anionic structural integrity. The structural gap between tetrahedral-unit-based metavanadate and octahedral-unit-based decavanadate structures may be linked by this hybrid complex.

Graphical abstractSpeciation studies of oxovanadate species are essential to clarify their biological reactivity. Acidification of oxovanadate in the presence of fluoride anion, which can be assimilated into the body, has a significant effect on the distribution of polyoxovanadate species, giving [V7O19F]4 − and [HV11O29F2]4 − successively.Figure optionsDownload full-size imageDownload as PowerPoint slide