Spectral and thermal studies of 4-(1H-pyrazolo {3,4-d} pyrimidin-4-ylazo) benzene-1,3-diol complexes of cobalt(II), nickel(II) and copper(II)

4-(1H-Pyrazolo {3,4-d} pyrimidin-4-ylazo) benzene-1,3-diol was synthesized and characterized by various spectral and analytical techniques. Semiempirical quantum calculations using the AM I method have been performed in order to evaluate the geometry and electronic structure of the title azodye in the ground state. The complex formation between Co(II), Ni(II) and Cu(II) ions and the title azodye was studied conductometrically and spectrophotometrically. The spectrophotometric determination of the title metal ions and titration using EDTA are reported. Co(II), Ni(II) and Cu(II) complexes of the title azodye have been synthesized and characterized by elemental analysis, conductivity, magnetic susceptibility, IR, UV-Vis and thermal analysis (TGA and DTA). The spectral and magnetic data suggested the octahedral geometry for Co(II) and Ni(II) complexes while Cu(II) complexes have square planar geometry. The thermal studies confirmed the chemical formulations of the title complexes. The thermal degradation takes place in two or three steps depending on the type of the metal and the geometry of the complexes. The kinetics of the decomposition was examined by using Coats-Redfern relation. The activation energies and other activation parameters (Delta H, Delta S and Delta G) were computed and related to the bonding and stereochemistry of the complexes. (C) 2007 Elsevier B.V. All rights reserved.