A New Mononuclear Copper(II) Complex Containing Two Imidazolyl Moieties as Precursor of Self-Assembled and Ni^IICu^IINi^II Heterobimetallic Complexes

A novel bis-imidazolyl tetradentate Schiff base ligand (H2L) has been prepared from the condensation of imidazole-2-carbaldehyde and 1,3-diaminopropane. The ligand reacts with copper(II) perchlorate in neutral medium to yield the mononuclear complex [Cu(H2L)(ClO4)]ClO4·H2O. A single-crystal X-ray diffraction study confirmed the expected structure, C11H16N6O9Cl2Cu, triclinic, P1̄, a = 8.875(2) Å, b = 10.842(2) Å, c = 10.888(2) Å, a = 68.09(3)°, b = 84.47(3)°, g = 70.96(3)°, Z = 2, in which the copper(II) ion occupies the inner N4 site of the nondeprotonated ligand. Under basic conditions [Cu(H2L)(ClO4)]ClO4·H2O can coordinate another metal ion through the deprotonated imidazole nitrogen atoms and simultaneously to accept a donor atom at the axial coordination site. This donor atom can belong to another deprotonated [Cu(L)] unit, giving rise, by a self-assembly process, to the polymer [Cu(L)]n. The crystal structure of this complex, C11H11N6Cu, orthorombic, Pbca, a = 18.132(12) Å, b = 14.927(6) Å, c = 8.629(4) Å, Z = 8, consists of zigzag chains formed by [Cu(L)] units, in which copper(II) ions are sequentially bridged by imidazolate groups, with a copper−copper distance of 5.993 Å. The variable-temperature magnetic susceptibility measurements revealed the existence of an antiferromagnetic interaction between copper(II) ions through the imidazolate bridge. The analysis of the magnetic data on the basis of the spin Hamiltonian H = −2∑JijŜi·Ŝj leads to J and g values of −1.2 cm-1 and 2.05, respectively. In addition, the reaction of [Cu(H2L)](ClO4)2·H2O with an excess of bis(hexafluorocetylacetonato)nickel(II) (Ni(hfac)2) in basic medium leads to the heterotrinuclear complex {Cu(L)(H2O)[Ni(hfac)2(H2O)]2}. The magnetic properties of this complex agree well with those expected for a NiIICuIINiII trinuclear system with irregular spin state structure and zero-field splitting of the quartet ground state. The analysis of the magnetic data leads to J = −25.4 cm-1, gNi = 2.07, gCu = 2.01, and D = ±4.0 cm-1.