NEW ROUTE TO BIMETALLIC IMIDAZOLE-BRIDGED COMPLEXES .4. SYNTHESIS AND CHARACTERIZATION OF HOMOBINUCLEAR (CU-CU-NI-NI) AND HETEROBINUCLEAR (CU-NI-CU-ZN-NI-ZN) IMIDAZOLATE-BRIDGED COMPLEXES FROM NOVEL MONONUCLEAR ENTITIES

A novel non-symmetrical tetradentate Schiff base, AE-ImH, resulting from the condensation of 7-amino- 4-methyl-5-aza-3-hepten-2-one (AEH) with imidazole- 2-carboxaldehyde, has been prepared and characterized. This ligand can react with copper and nickel ions to yield neutral MiAE-Im entities. When Mi is Cu, the mononuclear units are associated in the solid state to yield a chain structure. Subsequent reaction of the mononuclear units with MoAE entities (Mi for inner, Mo for outer metal coordination site relating to the AE-ImH ligand) or Zn(hfa)2·2H2O (hfa=anion of hexafluoroacetylacetone) gave homo- (CuCu; NiNi) and heterobinuclear (CuNi; CuZn; NiZn) imidazolate-bridged complexes [MiAE-ImMoAE]+ or MiAE-ImZn(hfa)2. A significant antiferromagnetic interaction is operative in the copper-copper complex (2J=-48 cm-1; g=2.08). NMR, ESR and electronic spectra confirm the existence of the dinuclear structure in solution. From the entire set of results we may assume that in the dinuclear complexes, the imidazolate ligand has a rather localized structure with two markedly different nitrogen atoms, viz. a pyrrolic nitrogen at the inner site and a pyridinic nitrogen at the outer site. © 1990.