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-(acetylacetone imine)-N'-(ortho-hydroxyl arylaldimine) (aryl = 3,5-dibromophenyl, 3-m ethylphenyl, 3,6-dimethylphenyl, 3,5-dichlorophenyl, 3,5-dibromoacetop henone), have been prepared and characterized for studies of the gener al structure of their copper(II) complexes and assessment of the subst ituent effects on central metal ions. Upon reaction with copper(II) io ns, 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 ha s been revealed by an X-ray crystallographic study of one of the compl exes, hydroxy-3,5-dibromoacetophenoneiminato)copper(II), which exhibit s an approximately square-planar geometry with a slight tetrahedron di stortion. An ESR study of the copper(II) complexes in solution indicat es electronic effects from substituents influence the reactivity of ce ntral metal ions. In addition, a key step in preparation of the unsymm etrical ligands has been dramatically improved to ensure synthetic rep roducibility and eliminate the decomposition of an intermediate, 7-ami no-4-methyl-5-azo-3-heptene-2-one, AMAHO. Thermal stability of the com plexes has been also evaluated to assess the compatibility of the two donating moieties. (C) 1997 Elsevier Science Ltd.