N-(SUBSTITUTED PHENYLHYDROXYNAPHTHYLALDIMINATE) NICKEL(II) COMPLEXES - A STRUCTURAL AND VIBRATIONAL STUDY

The crystal and molecular structure of bis-(N-phenyl-1-hydroxy-2-naphthylaldiminate) nickel(II) (1) have been determined by x-ray crystallography. The compound crystallizes in the triclinic space group P1, No. 2 with one molecule in the unit cell. The metal adopts a trans-planar tetracoordination geometry with N and O as electron donor atoms. The molecule is stepped with the planes of two naphthyl groups parallel, each one making a dihedral angle of 20.4-degrees with the coordination plane. The infrared spectrum and a normal coordinate treatment, based on a simplified molecular model, are discussed and related to the crystal structure. The bands near 390 and 290 cm-1 have been assigned to the Ni-O and Ni-N stretching vibrations, respectively. The corresponding force constants were estimated to be 1.28 and 0.78 mdyn angstrom-1. The influence of variation of the nature of the Schiff base ligand on structure 1 has been studied by including in the vibrational analysis the bis-N-(Y-phenyl)-2-hydroxy-1-naphthylaldiminate nickel(II) complexes, where substituents Y are o-OCH3 (2), M-OCH3 (3) and m-NO2 (4). The results indicated a slightly lower electronic density distribution on the chelate ring in complex 1, particularly on the Ni-O bond, suggesting a stability order 1 less-than-or-equal-to 2-4. This difference arises mainly from the position of the hydroxynaphthylaldiminate group.