Reactivity of alpha-benzoin oxime with vanadium: Synthesis and characterization of vanadium coordination compounds and polyoxovanadate adducts

摘要

The reactivity of an ethanolic solution of alpha-benzoin oxime with an aqueous solution of vanadium in the V, IV or III oxidation states was investigated for different values of pH (2 - 4.5) and different values of the ligand/metal ratio. Under these experimental conditions, the reaction of alpha-benzoin oxime (H2L1) with vanadium(V) leads to the formation of various compounds: (1) A dimeric coordination complex of the formula [V2O4(H2L1)(2)(L-2)(2)]. 3H(2)O in which L-2 is C6H5(C=O)(C=NO-)C6H5, the deprotonated oxidized form of alpha-benzoin oxime. (2) An orange-yellow decavanadate adduct of the formula Na-5[HV10O28(H2L1)(2)(HL2)(2)]. 6H(2)O. (3) A green mixed-valence decavanadate adduct of the formula Na-6[H5V10O28(HL2)(6)]. 10H(2)O. In all these compounds, ligand-metal redox reactions take place at room temperature which progressively lead to a reduction of vanadium(V) to vanadium(IV). Only one dimeric vanadium(IV) coordination compound of the formula [V2O4(HL2)(4)]. 0.5H(2)O was isolated. The reaction of alpha-benzoin oxime with vanadium(III) leads to a dimeric coordination complex of vanadium(IV) of the formula [V2O4(H2O)(2)(L-4)(4)] in which alpha-benzoin oxime was transformed to dibenzil (L-4) after hydrolysis and oxidation. Under inert atmospher (nitrogen), alpha-benzoin oxime does not form any complex with vanadium(III). It was hydrolysed to benzoin (HL3), vanadium(III) being the catalyst of the reaction. [References: 31]