The polynuclear complex formation of niobium(V) in sulfuric acid solutions was studied by potentiometry. Quantitative characteristics of niobium(V) polynuclear complexes were determined by graphical and calculation methods.
The electrode reaction equilibria of niobium complexes were studied potentiometrically in acidic perchlorate, sulfate, and perchlorate-sulfate solutions. A two-electron reaction was shown to occur at the mercury electrode. The compositions of the Nb(V) and Nb(III) complexes predominantly present in the solutions were established. Equations for the electrode reaction equilibria were proposed.