Exchange coupling in a bis(heterodinuclear) [Cu(II)Ni(II)](2) and a linear heterotrinuclear complex Co(III)Cu(II)Ni(II). Synthesis, structures and properties

摘要

Two heterometallic complexes [{Cu-II(HLOX)Ni-II(N-3)}(2)] and [(tmtacn)Co-III(mu-OH)Cu-II(LOX)Ni-II(OH2)(2)][ClO4](2) (tmtacn=1,4,7-trimethyl-1,4,7-triazacyclononane) containing the same [(CuNiII)-Ni-II] core embedded in an unsymmetrical dicompartmental imine-oxime ligand H4LOX have been synthesized and characterized. Their crystal structures show that the Cu-II resides at the N(oxime)(2)O(phenolate)(2) site and assumes a planar geometry. The Ni-II is six-co-ordinated and bound to an N2O4 donor array comprising two iminonitrogens, two phenolate oxygens and two axially co-ordinated H2O molecules. The cobalt(III) is low spin and six-co-ordinated. In DMF solution at 10 K the EPR spectra of the complexes exhibit a spin-doublet ground state with "inverted" g values which demonstrate the delocalization of the unpaired electron over the CuNi core. Magnetic susceptibility measurements over the range 2-290 K confirm that the paramagnetic nickel(II) and copper(II) centres are antiferromagnetically coupled, with values for the exchange coupling constant J through the phenolate oxygens of -115 cm(-1) and -130 cm(-1) respectively. Considering the dimer as a single tetranuclear unit, the coupling constant J' through the path Cu-N-O-Ni is very small (approximate to 1 cm(-1)) but positive (ferromagnetic coupling). [References: 54]