Equilibrium processes in the system of vanadyl (2) ion -hydrazide of isonicotinic acid

Method of proton magnetic relaxation was used to study the system of vanadyl (2) ion - hydrazide of isonicotinic acid in -1-4 pH range. It is shown that formation of VOH2HL4+ (1) and VOHHL3+ (2) complex forms takes place in the region of pH values of -0.5-0.3 and 0.3-1.5 repspectively. Values of equilibrium constants of 1 and 2 complex formation lgK1 and lgK2, equal to 1.5±0.1 and -0.7±0.1 respectively, were calculated. Deprotonation of complex 2 with formation of difficultly soluble compounds, containing, probably, two molecules of deprotonated ligand, takes place at pH>2.5. The calculated constant of deprotonation is equal to 1.1±0.1