Equilibrium and structural studies of copper(II) and nickel(II) complexes with pyridine-2,6-diamidoxime in aqueous solution

The complex formation equilibria of copper(II) and nickel(II) with pyridine-2,6-amidoxime (H2L) were studied in aqueous 0.1 M NaCl solution at 25°C by potentiometric titrations with use of a glass electrode. Experimental data were analyzed with the least-squares computer program SUPERQUAD to determine the complexes formed and their stability constants. The best model included both metal ions in the mononuclear complexes M(H2L)2+, , M(H2L)HL+ and M(HL)2 and with nickel(II) also the complexes Ni(HL)L− and . The structure of the crystallized complex with the formula [Ni(HL)2]·4H2O was determined by X-ray diffraction. The crystal structure is orthorhombic, space group pbcn with a = 12.601(3), b = 9.3990(19), c = 17.195(3) Å, α = β = γ = 90° and Z = 4.