A NOVEL SERIES OF HETEROTRINUCLEAR COMPLEXES INVOLVING IMIDAZOLATE BRIDGING SCHIFFS BASE LIGANDS - SYNTHESIS, CRYSTAL-STRUCTURE, AND MAGNETIC-PROPERTIES

Mononuclear copper(II) complexes with an unsymmetrical tridentate Schi ffs base involving two imidazole moieties, [Cu(HL)(H2O)]ClO4)(2) (1) a nd [Cu(L)(hfac)] (3), have been prepared and characterized, where HL s tands for the 1:1 condensation product of 2-imidazolecarboxaldehyde an d histamine. Under basic conditions, 1 easily undergoes a self-assembl y process affording an insoluble imidazolate-bridged polymeric species ([Cu(L))(H2O)] (ClO4))(n) (2). By using 1 and 3 as ''ligand complexes '' toward M(hfac)(2) (hfac = hexafluoroacetylacetonate) a series of im idazolate-bridged heterometal trinuclear complexes with the formula [C u(L)(hfac)M(hfac)(2)Cu(hfac)(L)] (M = Zn-II, Cu-II, Ni-II, Mn-II) (4-7 ) can be prepared. The structures of these complexes have been solved by X-ray crystallographic methods. All the trinuclear complexes are is ostructural and consist of trinuclear molecules with a V-shaped confor mation, which are formed by two CuL(hfac) ''ligands'' bonded through i midazolate bridges to the central metal in cis-position. The ligand en vironment about the central metal atom can be described as a distorted octahedron, with the nitrogen atoms from the imidazolate groups and t wo oxygen atoms of the hfac ligands in the equatorial plane and the re maining two oxygen atoms from the hfac ligands filling the axial posit ions at longer distances. The coordination geometry of the copper(II) ion is very close to a square pyramid with one oxygen atom from the hf ac in a more distant axial position. The magnetic susceptibility data (2-300 K) revealed antiferromagnetic interactions between copper(TI) i ons and the central metal. The magnetic susceptibility data were quant itatively analyzed using the theoretical expressions deduced from the spin Hamiltonian for a symmetrical three-spin system H = -J(CuM)(S-Cul . S-M + SM .SCu2) to give the coupling parameters J(CuCu) = -60.6 cm(- 1), J(CuNi) = -21.6 cm(-l), and J(CuMn) = -3.2 cm-l. These magnetic be haviors are discussed on the basis of the localized-orbital model of e xchange interactions.