Spectral, magnetic, electrical and thermal studies on malonyl bis(thiosemicarbazide) complexes

Mono- and binuclear complexes of malonyl bis(thiosemicarbazide), H4MBT, with VO2+, Co2+, Ni2+, Cu2+, Cd2+ and Pt4+ have been isolated. The elemental analyses, magnetic moments, spectra [u.v.-vis., i. r., e. s. r. (for Cu2+; VO2+) and mass], thermal and voltammetric measurements [for Co2+ and Ni2+] have been used to characterize the isolated complexes. The ligand behaves as binegative quadridentate with Cu2+, Co2+ and VO2+ ions, binegative pentadentate with Pt4+ and hexadentate, either as trinegative in [Cd-2(HMBT)(OC2H5)(C2H5OH)]H2O or mononegative in [Ni-2(H3MBT)(OAc)(3)(C2H5OH)]. The lack of thiol and/or enol hydrogen during the complex formation was confirmed pH-metrically. The pK's (10.70, 8.50 and 8.15) of H4MBT reveal the removal of CSNH protons in one step and CONH in two steps. Also, the stability constants reveal a higher value for the Cu2+ complex and a lower one for VO2+. The TG analyses suggest high stability for most complexes followed by thermal decomposition in different steps. The kinetic and thermodynamic parameters for some decomposition steps in VO2+ and Pt4+ thermograms have been calculated.