Molecular association, chelate conformation and reactivity correlations in substituted o-phenylenebis(salicylidenato)copper(II) complexes: UV-visible, EPR and X-ray structural investigations

Abstract

Substituted o-phenylenesbis(salicylidenaminato) complexes of copper(II), Cu(5-X-saloph), where X = H (1), CH3O (2) and Cl (3) have been synthesized and characterized. Complex 1, C20H14N2O2Cu, crystallizes in the orthorhombic space group P212121 with two molecules (A and B) in the assymetric unit related by a non-crystallographic centre of inversion and the nitrogen atom of A coming closer to the metal ion of B and vice versa. The geometry around copper is essentially square planar in both A and B with average Cu---N and Cu---O bond distances being 1.89(2) and 1.95(2) →ing chelate conformation is also planar with a moderate “twist” at the “sal” groups. EPR spectra of the complexes are characterized by axial or rhombic g and ACu tensors and indicate the occupancy of an unpaired electron in a “formal” dxy orbital. Solutions at 298 K showed superhyperfine features due to interaction of transferred unpaired spin with the nuclear spin of two magnetically equivalent 14N nuclei and the protons attached to adjacent methylene carbon atoms. The complexes exhibit solvatochromism. Substitution and δ-donor solvents show marked effects on the UV-visible and EPR spectra. MO calculations reveal that the in-plane δ and π bondings are covalent in nature. The correlation between conformational flexibility and reactivity is discussed.