Three nickel(II) complexes, (5-bromo-2-hydroxybenzaldehyde S-ethylisothiosemicarbazonato-N,N0 , O)-(imidazole)-nickel(II) (1), (5-bromo-2-hydroxybenzaldehyde S-ethylisothiosemicarbazonato-N,N0,O)- (4-dimethylaminopyridine)-nickel(II) (2) and (S-ethyl-1,4-bis(5-bromo-2-hydroxybenzaldehyde)- isothiosemicarbazido-O,O0,N,N0)-nickel(II) (3) have been synthesized and characterized by elemental analysis, molar conductivity, FT-IR, 1H NMR and UV–Vis studies. For better definition of the molecular structures, the X-ray crystallographic analysis was carried out for the complexes. The complexes 1 and 2 show distorted square planar geometry around the central Ni(II) ion, with the ligand coordinated to the central metal as a tridentate chelate and the fourth coordination position occupied by imidazole and 4-dimethylaminopyridine in 1 and 2 respectively. Compound 3 also adopts a distorted square planar geometry with the tetradentate ligand occupying all coordination positions around the metal center. The deprotonated form of the N2O2 donor ligand is coordinated to nickel(II) via both deprotonated phenolic oxygen and azomethine nitrogen atoms. The complexes have been investigated by DFT calculation and the results were compared with the crystallographic data.

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