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

Abstract

Complexes with stoichiometry [Ni(L)X2], where L is a tridentate ligand, 1,5-bis-(benzimidazol-2-yl)-3-thiapentane, have been synthesized and characterised. The presence of an electronic absorption band in the region of ≥ 25000 cm^-1 is indicative of six coordinated tetragonal complex in solution. The parameter 10Dq varies as: X= NO₃^- > CH₃COO^-> HCOO^- > SCN^- > Cl^- . ¹H 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 dominant σ spin delocalisation mechanism: the same is confirmed by the shifts of the ¹³C NMR data which lie in the range of +74.0 to + 181.0 ppm with respect to TMS. No doubling of peaks is observed in the NMR spectra, implying a mirror plane or <i>C</i>₂ axis of symmetry in the complexes. The <i>E</i>_1/2<i> </i>data indicate that the ease of reduction follows the order: > Cl^- ˃ NO₃^- > CH3COO^-.