A fresh look into VO(salen) chemistry: synthesis, spectroscopy, electrochemistry and crystal structure of [VO(salen)(H2O)]Br · 0.5 CH3CN

The reaction of VIVO(salen) with [Et4N][SnBr3] in air proceeds via an initial reduction to give a [VIII (salen)]+ intermediate, which is then oxidised to dark green [VVO(salen)(H2O)]Br, 1. As determined by X-ray crystallography, 1 in the solid state contains hexacoordinate vanadium. 51V NMR spectra indicate that dissociation of the aqua ligand occurs to give a pentacoordinated [VVO(salen)] cation in methanol-d4 solution, while in DMSO-d6 solutions, coordination of the solvent occurs to give [VVO(salen)(DMSO-d6)]+. The colour of 1 can be accounted for by Ooxo → VV and phenolate → VV LMCTs. Results from this study have led to the re-assignment of LMCTs and V–N and V–Ophenolate stretching frequencies in the IR spectrum. Cyclic voltammetry of 1 indicates three redox processes. The first is typical of [VO(salen)]/[VO(salen)]+ couple and the other two are bromide oxidations.