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 via 1H 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.