A comprehensive overview of the orientation of tetradentate N2O2 donor Schiff base ligands in octahedral complexes of trivalent 3d metals

Abstract

Trivalent 3d metal complexes having the general formula [MIII(L)(X)(Y)] [where H2L represents the tetradentate N2O2 donor ‘salen type’ Schiff base, and X and Y are monodentate ligands], which were characterized by single crystal X-ray diffraction studies, have been analyzed in this review. In any octahedral complex of tetradentate N2O2 donor ‘salen type’ Schiff base ligand, two different arrangements of four donor atoms (two imine nitrogen atoms and two phenoxy oxygen atoms) around the metal centre are found. In one arrangement, the equatorial positions of M(III) are occupied by the respective deprotonated tetradentate ligands, whereas the axial positions are occupied by monodentate ligands. The second group of complexes follows a different arrangement where one oxygen atom is displaced from the equatorial plane, occupying an axial position of the coordination octahedron. The formation of the complexes of second type is favoured by the presence of a chelating bidentate ligand occupying two cis positions. On the other hand, the tetradentate ligands in the first type of complexes have also been found to be severely distorted from planarity in some complexes. This distortion may be quantified by measuring the angle between the plane of the phenyl ring(s) of the ligand and the equatorial plane of the complex.