Synthesis and characterization of a new N2S2 Schiff base ligand and its complexes with nickel(II), copper(II) and cadmium(II) including the kinetics of complex formation

The new Schiff base phthaldihyde-bis(4-methyl-3-thiosemicarbazone) (PHMTSC) was synthesized from the condensation of phthaldihyde with 4-methyl-3-thiosemicarbazide. Monomeric complexes of this ligand, of general formulae [M(PHMTSC-2H(+))], are reported. The mode of bonding and overall geometry of the complexes were determined through physicochemical and spectroscopic methods. These studies revealed square planar geometries for the Ni(II) and Cu(II) complexes, and tetrahedral geometry for the Cd(II) complex. The kinetics of the reactions between PHMTSC and all the various metal salts has been determined by stopped-flow spectrophotometry. In all cases, the reactions are complete on the second's timescale. The reactions exhibit a first-order dependence on the concentration of metal salt and a first-order dependence on the concentration of PHMTSC. The thermodynamic and kinetic factors influencing the protonation state of the coordinated thiosemicarbazone are discussed.