An electron spin resonance study on the interactions between bis-(pentane-2,4-dionato)copper(II) and some heterocycles. Part 2. The 1 : 1 adducts with aza-aromatic compounds and azacyclohexanes
Abstract
E.s.r. spectra of a series of Cu(acac)2 adducts of aza-aromatic compounds and azacyclohexanes (L) were measured. The 1 : 1 adduct Cu(acac)2L is formed almost exclusively in chloroform solution, L occupying an apical site. Their g∥ and |A∥| values were determined in order to investigate the steric and electronic effects on co-ordination. When the frontal steric hindrance of the base is not large, the |A∥| values of Cu(acac)2L are linearly related to the pKa values of L. Since the nitrogen atoms in 2,6-dimethylpyridine, 2- and 8-methylquinoline, acridine, and N-methylazacyclohexanes have considerable frontal steric hindrance, remarkable deviations from the straight line are observed for these compounds. The presence of two 1 : 1 adducts is shown for N-methylmorpholine, the O-adduct being more favourable than the N-adduct because of steric hindrance.