H-1 AND C-13 MAGNETIC-RESONANCE INVESTIGATION OF NICKEL(II) COMPLEXES OF BIS-BENZIMIDAZOLYL LIGANDS

Nickel(II) complexes of tridentate ligands bis(2-benzimidazolyl methyl) ether, sulphide and their N-butyl derivatives have been synthesized and characterized. The H-1 NMR spectra of nickel(II) complexes depict dipolar broadened, isotropically contact shifted resonances in the range of +0.7 to +53.0 ppm, typical of high spin nickel(II), while C-13 NMR spectra have resonances in the range of +98.0 to +278.0 ppm with respect to TMS. The sign of the shifts is indicative of dominant sigma-spin delocalization mechanism. The present contact shift data also reveal that the benzimidazole ring protons experience an equivalent ligand held environment, indicating a plane or C-2 axis of symmetry in the molecules. The stoichiometry of the present complexes is suggestive of five-coordinate geometry in the solid state. However, the presence of an electronic absorption band in the region greater than or equal to 25,000 cm(-1) is indicative of a six-coordinated tetragonal complex in solution.