Synthetic, structural and kinetic studies on the binding of cyclohexane-1,2-bis(4-methyl-3-thiosemicarbazone) to divalent metal ions (Co, Ni, Cu, Zn or Cd).

The reactions of cyclohexane-1,2-bis(4-methyl-3-thiosemicarbazone) (CHMTSC) with MCl2 (M = Co, Ni, Cu or Zn) and Cd(NO3)2 have been shown to produce complexes in which the thiosemicarbazone has been doubly deprotonated [[M(CHMTSC - 2H+)] (M = Co, Ni or Ni)], analogous to those reported earlier with other Schiff base thiosemicarbazones. However, with ZnCl2 and Cd(NO3)2, the complexes isolated are [ZnCl(CHMTSC)]Cl and [Cd(NO3)(CHMTSC)]NO3, containing the protonated forms of the ligand, which have been characterised by X-ray crystallography, as has free CHMTSC. The kinetics of the reactions between CHMTSC and all the various metal salts have been determined by stopped-flow spectrophotometry. In all cases, the reactions are complete on the seconds timescale. The reactions exhibit a first-order dependence on the concentration of metal salt and a first-order dependence on the concentration of CHMTSC. The thermodynamic and kinetic factors influencing the protonation state of the coordinated thiosemicarbazone are discussed.