Synthesis and characterization of nickel(II) complexes with 1,5-bis(benzimidazol-2-yl)-3-thiapentane

Complexes with stoichiometry [Ni(L)X-2], where L is a tridentate ligand, 1, 5-bis-(benzimidazol-2-yl)-3 -thiapentane, have been synthesized and charact erised. The presence of an electronic absorption band in the region of grea ter than or equal to 25000 cm L is indicative of six-coordinated tetragonal complex in solution. The parameter 10Dq varies as: X = NO3- > CH3COO-> HCO O- > SCN- > Cl-.H-1 NMR contact-shifted resonances lie in the range of -19. 0 to +55.0 ppm, typical of high spin Ni(II) and do not show any significant dependence on Dq. The sign of the contact shifts is indicative of a domina nt sigma spin delocalisation mechanism: the same is confirmed by the shifts of the C-13 NMR data which lie in the range of +74.0 to +181.0 ppm with re spect to TMS. No doubling of peaks is observed in the NMR spectra, implying a mirror plane or Ct axis of symmetry in the complexes. The E-1/2 data ind icate that the ease of reduction follows the order: Cl- > NO3- > CH3COO-.