Spectral, Magnetic, Electrical and Thermal Studies on Malonyl bis(thiosemicarbazide) Complexes

Abstract

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.

Biheterocyclic ligands: synthesis, characterization and coordinating properties of bis(4-amino-5-mercapto-1,2,4-triazol-3-yl) alkanes with transition metal ions and their thermokinetic and biological studies

“…The bands at 1240-1253 cm -1 in the spectra of the ligands assigned to ν(C=S) is lowered by 8-88 cm -1 in the spectra of the complexes, indicating involvement of thione groups sulfur in the coordination. This leads to new bands in the region 350-385 cm -1 tentatively assigned to M-S vibration [27].…”

“…A broad IR band in the range 3142-3474 cm -1 in the complexes is attributed to the overlapping vibration of νNH(NH 2 ) with that of νOH(H 2 O) of coordinated water [26]. Coordinated water shows metal-oxygen ν(M-O) stretching vibration in the 426-480 cm -1 [27]. The appearance of the four thioamide bands (I-IV) at 1570 -1581, 1302 -1327, 920 -982 and 745 -781 cm -1 [27], refutes the presence of the bands in the 2400-2600 cm -1 regions and at 606 cm -1 due to ν(SH) and ν(C-S), respectively [28] confirming that the ligands of BATs exist mainly in the thione form [5].These four thioamide bands of the ligands are compared with those of their complexes in Table 2, indicating the shift due to complexation.…”

“…Coordinated water shows metal-oxygen ν(M-O) stretching vibration in the 426-480 cm -1 [27]. The appearance of the four thioamide bands (I-IV) at 1570 -1581, 1302 -1327, 920 -982 and 745 -781 cm -1 [27], refutes the presence of the bands in the 2400-2600 cm -1 regions and at 606 cm -1 due to ν(SH) and ν(C-S), respectively [28] confirming that the ligands of BATs exist mainly in the thione form [5].These four thioamide bands of the ligands are compared with those of their complexes in Table 2, indicating the shift due to complexation. The bands at 1240-1253 cm -1 in the spectra of the ligands assigned to ν(C=S) is lowered by 8-88 cm -1 in the spectra of the complexes, indicating involvement of thione groups sulfur in the coordination.…”

“…In addition, the shift in ν(C=N), for C=N being adjacent to N-N in the molecular structure, is to lower frequency by 4-108 cm -1 [13]. Coordination through the amino groups nitrogen is consistent with new bands in the 400-406 cm -1 , assignable to the ν(M-N) vibration [23,27,30]. The new band at the low frequency 325-359 cm -1 is assigned to ν(M-Cl).…”

“…Table 3 compares the magnetic moments, electronic spectral data and ligand field parameters of the Co(II), Ni(II) and Cu(II) complexes with the ligands of BATs. The electronic spectrum of the ligands BAT2 and BAT3 exhibit their two absorption maxima in the ranges 42194 -33333 cm -1 and 42373-33112 cm -1 , assignable to π→π* (K-band) and n→π* (R-band) transitions [27], respectively, (Table 3).…”