Methylene spacer regulated variation in conformation of tetradentate N2O2 donor Schiff bases trapped in manganese(iii) complexes

Abstract

Seven mononuclear manganese(III) complexes having the general formula [Mn(L)(X)(Y)] [where H₂L represents the tetradentate N₂O₂ donor salen-type Schiff base, and X and Y are monodentate ligands, e.g. pseudohalide, DMSO, H₂O, etc.] have been prepared and characterized by single crystal X-ray diffraction studies. Manganese(III) in each complex shows a six-coordinate distorted octahedral geometry. The equatorial positions of manganese(III) are occupied by the respective deprotonated tetradentate ligands, whereas the axial positions are occupied by monodentate ligands. The use of ethylenediamine or its derivative to prepare the H₂salen-type Schiff bases essentially produces manganese(III) complexes containing more or less planar salen²⁻ moieties. Incorporation of one methylene spacer in the diamine moiety gives manganese(III) complexes containing salen²⁻ ligands, significantly distorted from planarity. This distortion has been be quantified by measuring the angle between the plane of the phenyl ring(s) of the ligand and the equatorial plane of the complex. The energy associated with the formation of supra-molecules via non-covalent interactions was also estimated by DFT calculation. Bader's theory of “atoms in molecules” has been used to analyze the π-stacking interactions observed in the solid state of these complexes.