MOLECULAR ASSOCIATION, CHELATE CONFORMATION AND REACTIVITY CORRELATIONS IN SUBSTITUTED O-PHENYLENEBIS(SALICYLIDENAMINATO)COPPER(II) COMPLEXES - UV-VISIBLE, EPR AND X-RAY STRUCTURAL INVESTIGATIONS

Substituted o-phenylenebis(salicylidenaminato) complexes of copper(II) , Cu(5-X-saloph), where X = H (1), CH3O (2) and Cl (3) have been synth esized and characterized. Complex 1, C20H14N2O2Cu, crystallizes in the orthorhombic space group P2(1)2(1)2(1) with two molecules (A and B) i n the asymmetric unit related by a non-crystallographic centre of inve rsion and the nitrogen atom of A coming closer to the metal ion of B a nd 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) Angstrom, respectively. The overall chelate conformatio n is also planar with a moderate ''twist'' at the ''sal'' groups. EPR spectra of the complexes are characterized by axial or rhombic g and A (Cu) tensors and indicate the occupancy of an unpaired electron in a ' 'formal'' d(xy) orbital. Solutions at 298 K shoved superhyperfine feat ures due to interaction of transferred unpaired spin with the nuclear spin of two magnetically equivalent N-14 nuclei and the protons attach ed to adjacent methylene carbon atoms. The complexes exhibit solvatoch romism, Substitution and sigma-donor solvents show marked effects on t he UV-visible and EPR spectra. MO calculations reveal that the in-plan e sigma and pi bondings are covalent in nature. The correlation betwee n conformational flexibility and reactivity is discussed. Copyright (C ) 1996 Elsevier Science Ltd