A pro-chiral bis-imidazolyl-containing copper(II) complex as precursor of a self-assembled polymer and a heterodinuclear copper(II)-nickel(II) complex

A bis-imidazolyl tetradentate Schiff base ligand, H2L, was prepared from the condensation of imidazole-2-carbaldehyde and 1,3-diamine-2-propanol. A 1D H-1 and 2D H-1 COSY NMR spectroscopic study established the non-symmetry of the ligand and the existence of an asymmetric carbon atom. The ligand reacts with copper(II) perchlorate in neutral medium to yield the mononuclear complex [Cu(H2L)(H2O)](ClO4)(2). As expected, X-ray crystal study confirms that the copper(II) ion occupies the inner N-4 site of the non-deprotonated ligand. In basic medium the complex [Cu(H2L)(H2O)](ClO4)(2) polymerises by a self-assembly reaction to [Cu(L)](n). This process is reversible and, at acid pH, the polymer structure dissociates into mononuclear units. In basic medium and in the presence of an excess of nickel(II)bishexafluoracetylacetonate, [Ni(hfa)(2)], a complex with two available coordination sites, it is possible to avoid the self-assembly reaction and to obtain a heterobimetallic copper(II)-nickel(II) system by the coordination of one of the imidazolate groups to the nickel(II) ion. The fact that only one of the two imidazolate groups coordinates a nickel(II) ion reveals the chemical asymmetry of the copper(II) complex. (C) 2000 Elsevier Science S.A. All rights reserved.