Mono-and binuclear complexes of malonyl bis(thiosemicarbazide), H 4 MBT, with VO 2+ , Co 2+ , Ni 2+ , Cu 2+ , Cd 2+ and Pt 4+ have been isolated. The elemental analyses, magnetic moments, spectra [u.v.-vis., i.r., e.s.r. (for Cu 2+ ; VO 2+ ) and mass], thermal and voltammetric measurements [for Co 2+ and Ni 2+ ] have been used to characterize the isolated complexes. The ligand behaves as binegative quadridentate with Cu 2+ , Co 2+ and VO 2+ ions, binegative pentadentate with Pt 4+ and hexadentate, either as trinegative in [Cd 2 (HMBT)(OC 2 H 5 )(C 2 H 5 OH)]H 2 O or mononegative in [Ni 2 (H 3 MBT)(OAc) 3 (C 2 H 5 OH)]. 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 H 4 MBT reveal the removal of CSNH protons in one step and CONH in two steps. Also, the stability constants reveal a higher value for the Cu 2+ complex and a lower one for VO 2+ . 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 VO 2+ and Pt 4+ thermograms have been calculated.

The coordination behaviour of phthaloyl bis(thiosemicarbazide), H 4 PBT, towards VO 2þ , Co(II), Ni(II), Cu(II), Zn(II) and UO 2þ 2 ions has been investigated. The elemental analyses, magnetic moments, spectra [UV-Vis, IR, ESR and MS] and thermal studies were used to characterize the isolated complexes. Cyclic voltammetry was used to study the electrochemical behaviour of the Cu(II) complex. The IR spectra showed that the ligand is deprotonated in the complexes and acts as a binegative SSNN donor. The f U-O (mdyn Å À1 ) and the length r UÀO (Å ) of the UO bond are calculated spectroscopically from the IR data. The loss of thiol hydrogen during the formation of complexes was confirmed from the pH-metric titrations of the ligand and its metal(II) complexes. The protonation constants of the ligand (pK 1 ¼ 9.45 and pK 2 ¼ 7.25) as well as the stability constants of its complexes were calculated. The intensity and position of the V¼O band in the IR spectra reflect the geometry of the formed complex. Also, its colour (dark green) is consistent with the suggested stereochemistry. The binuclear VO 2þ complex was isolated and confirmed by ESR spectra. The TG analyses for the VO 2þ , Co(II), Ni(II) and Zn(II) complexes suggest different decomposition steps. The CoatsRedfern and Horowitz-Metzger equations have been used to calculate the kinetic and thermodynamic parameters for the different thermal decomposition steps of some complexes. The redox properties, nature of the electroactive species and the stability of the Cu(II) complex toward oxidation were examined. The electrochemical data are discussed in terms of the kinetic parameters and the reaction mechanism.

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