Site-selective halogenation of mixed-valent vanadium oxide clusters.

Here, we expand on the synthesis and characterization of chloride-functionalized polyoxovanadate-alkoxide (POV-alkoxide) clusters, to include the halogenation of mixed-valent vanadium oxide assemblies. These findings build on our previously disclosed results describing the preparation of a mono-anionic chloride-functionalized cluster, [V6O6Cl(OC2H5)12]1-, by chlorination of [V6O7(OC2H5)12]2- with AlCl3, aimed at understanding the electronic consequences of the introduction of halide-defects in bulk metal oxides (e.g. VO2). While chlorination of the mixed-valent POV-ethoxide clusters was not possible using AlCl3, we have found that the chloride-substituted oxidized derivatives of the Lindqvist vanadium-oxide clusters can be formed using TiCl3(thf)3 with [V6O7(OC2H5)12]n (n = 1-, 0) or WCl6 with [V6O7(OC2H5)12]0. Characterization of the chloride-containing products, [V6O6Cl(OC2H5)12]n (n = 0, 1+), was accomplished via1H NMR spectroscopy, X-ray crystallography, and elemental analysis. Electronic analysis of the redox series of Cl-doped POV-alkoxide clusters via infrared and electronic absorption spectroscopies revealed all redox events are localized to the vanadyl portion of the cluster, with the site differentiated VIII-Cl moiety retaining its reduced oxidation state across a 1.9 V window. These results present new synthetic routes for accessing chloride-doped POV-alkoxide clusters from mixed-valent vanadium oxide precursors.