Synthesis and spectroscopic characterization of nickel(II) complexes of 1-benzotriazol-1-yl-[( p-X-phenyl)hydrazone]propan-2-one

Abstract

The reaction of NiCl 2·H 2O with 1-benzotriazol-1-yl-[( p-X-phenyl)hydrazone]propan-2-one, X = H (HL 1), X = Cl (HL 2), X = Br (HL 3) and X = Me (HL 4), gave the complexes [(HL)NiCl 2]· nH 2O and [LNi(OH)] 2, where L is the monobasic anion of HL 2 or HL 3. The nature of the products is solvent and ligand dependent. The complexes are characterized by elemental analyses, molar conductivity, magnetic moments and spectroscopic (IR and UV/vis) measurements. The IR showed that the ligands act as neutral bidentate coordinated to the nickel(II) through the azomethine nitrogen and carbonyl oxygen atoms in case of [(HL)NiCl 2]· nH 2O. In case of [LNi(OH)] 2, the ligands are monobasic bidentate bonded to the nickel(II) through the azomethine nitrogen and the enolato oxygen atoms. The room temperature magnetic moment values of 1.58–2.49 B.M. for [(HL)NiCl 2]· nH 2O and [LNi(OH)] 2 and their electronic spectral data indicate that these complexes have square planar–tetrahedral equilibrium. The values of 1.61 and 1.58 B.M. for the hydroxo-complexes support their dimeric nature. The electronic spectral of [(HL)NiCl 2]· nH 2O and [LNi(OH)] 2 in pyridine or α-picoline indicated the formation of six-coordinate adducts. The hydroxo-complexes reacted with different Lewis bases to give the complexes [L 2Ni(L s) 2], where L s = Py, 2-Pic, 3-Pic, 4-Pic or n-PrNH 2. The relationship between the p K b of the Lewis base and the υ Ni–O of the ligand and υ Ni–N of the Lewis base was studied. The different ligand field parameters are calculated for the parent ligands in solutions and the solid mixed ligand complexes. The data showed that both are associated with a distorted octahedral ligand field around the nickel(II) and the ligand fields in solution are different from that in solid. The extent of distortion for the parent complexes is more than that in the solid adducts. Furthermore, the data showed that the nickel–ligand bonding in [LNi(OH)] 2 is more covalent than in [L 2Ni(L s) 2].