STERIC-HINDRANCE EFFECT OF A SUBSTITUENT IN THE SELF-ASSEMBLY PROCESSOF COPPER(II) COMPLEXES WITH QUADRIDENTATE SCHIFF-BASE LIGANDS INVOLVING A 2-SUBSTITUTED-IMIDAZOLE MOIETY

Four copper(II) complexes with unsymmetrical quadridentate ligands inv olving an imidazole moiety, [CuHLn]-ClO4 (1-4; n = 1-4), have been pre pared and characterized, where HL1 = cylidene-N'-(2-methylimidazol-4-y lmethylidene)-1,3 -propanediamine, HL2 = henylimidazol-4-ylmethylidene )-1,3-propanediamine, HL3 = (2-methylimidazol-4-ylmethylidene)ethylene diamene, HL4 = (2-phenylimidazol-4-ylmethylidene)ethylenediamine, resp ectively. The corresponding deprotonated complexes 1'-4' were obtained when 1-4 were treated under an alkaline condition. Deprotonation of t he imidazole moiety of the copper(II) complex motivates a self-assembl y process which is formed by an axial coordination of the imidazolate nitrogen atom of a molecular unit to the copper(II) ion of another uni t. 1'-3' assumes a self-assembled imidazolate-bridged infinite-chain s tructure {Cu(II)-Im}(n) in the solid state, while the polymeric specie s dissociates to monomeric species in the solution state. 4' consists of a discrete deprotonated monomeric species, even in the solid state. The physical measurements, including reflectance and absorption spect ra, cryomagnetic measurements, and single-crystal X-ray analyses, reve aled that the self-assembly behavior for the series of copper(II) comp lexes depends both on the steric effect of the substituent of 2-substi tuted-4-formylimidazole moiety and the ligand field strength of the eq uatorial quadridentate ligand.