Host-guest chemistry of vanadium-oxygen molecular anions

Abstract

The structure-dependent unique host-guest chemistry of the bowl-shaped inorganic vanadium-oxygen cluster anion, [V₁₂O₃₂]^4– (V12), is reviewed. The half-spherically ordered square-pyramidal VO₅ units form the relatively positively charged concave inside. It stabilizes anionic moiety at the concave, even though the host itself possesses negative charge. Unusual anions such as nitroxyl anion, NO^–, and deprotonated nitromethane anion, CH₂NO₂^–, are also stabilized in V12. The guest-exchange, -removal and -inclusion of the V12 host are demonstrated. The removal of a guest causes a flip of one of the VO₅ pyramidal units, and the inclusion retrieves the structure. The incorporation of a bromine molecule induces the polarization of bromine molecule, and it provides brominated products of alkanes with unique selectivity. The lid effect of a cation above the concave controls the depth and orientation of a guest. An inert tetraethylammonium cation acts as a lid. Azide, N₃^–, is forced to be laid down in the concave with elliptically distorting the V12 host. The lid cation also affects the oxidation catalytic property of V12.