New copper(II) complexes incorporating unsymmetrical tetradentate ligands with cis-N2O2 chromophores: Synthesis, molecular structure, substituent effect and thermal stability

Five new tetradentate unsymmetrical ligands, ethylene-N-(acetylacetoneimine)-N'-(ortho-hydroxyl arylaldimine) (aryl = 3,5-dibromophenyl, 3-methylphenyl, 3,6-dimethylphenyl, 3,5-dichlorophenyl, 3,5-dibromoacetophenone), have been prepared and characterized for studies of the general structure of their copper(II) complexes and assessment of the substituent effects on central metal ions. Upon reaction with copper(II) ions, the ligands derived from aryls, where aryls are 3,5-dibromophenyl, 3-methylphenyl, 3,6-dimethylphenyl and 3,5-dibromoacetophenone, give the corresponding copper(II) complexes while the ligand derived from 3,5-dichlorophenyl undergoes partial hydrolysis leading to the cleavage of an acetylacetone moiety. The general coordination configuration has been revealed by an X-ray crystallographic study of one of the complexes, ethylene-N-(acetylacetoneiminato)-N'-(o-hydroxy-3,5-dibromoacetophenoneiminato)copper(II), which exhibits an approximately square-planar geometry with a slight tetrahedron distortion. An ESR study of the copper(II) complexes in solution indicates electronic effects from substituents influence the reactivity of central metal ions. In addition, a key step in preparation of the unsymmetrical ligands has been dramatically improved to ensure synthetic reproducibility and eliminate the decomposition of an intermediate, 7-amino-4-methyl-5-azo-3-heptene-2-one, AMAHO. Thermal stability of the complexes has been also evaluated to assess the compatibility of the two donating moieties. (C) 1997 Elsevier Science Ltd.