The Nb(V) reduction in acetonitrile, containing up to 10 mM residual water, was investigated as a function of chloride and Nb(V) concentrations. The effect caused by hydrogen chloride and a proton donor was also examined. Before any electron transfer occurs NbCl5 initially hydrolyzes resulting in HCl and hydroxy-species, all being in equilibrium. Nb(IV) formed after a monoelectronic reduction can either hydrolyze, yielding an electroinactive species, or, depending on experimental conditions used, dimerize (in TEAP) or disproportionate (in TEACl). Futher reduction of Nb(IV) is possible in tile presence of chloride, which acts as a stabilizing agent. Nb(IV) hydrolysis yields HCl whose reduction wave overlaps with the peaks from futher Nb(IV) reduction. Nb(IV) does not hydrolyze if adequate amounts of HCl and/or TEACl are present in solution. A comparison is made between simulation of the proposed electrode mechanism and experimental data.
electrochemistry; niobium; reduction; non-aqueous solvent
