Syntheses, Structure and Magnetism of Heterobinuclear mi-Oxamido Cu(II)-Ni(II) Complexes Containing tacn as a Terminal Ligand

Two new heterobinuclear complexes, namely Ni(tacn)Cu(oxpn)(ClO 4 ) 2 .2H 2 O (1) and Ni(tacn)Cu(pmoxd)(ClO 4 ) 2 .CH 3 OH (2), have been prepared from the planar fragments Cu(oxpn) and Cu(pmoxd) (tacn denotes 1,4,7-triazacyclononane, oxpn and pmoxd stand for the dianions of N,N'-bis(3-aminopropyl)oxamide and N,N'-bis(2-pyridylmethyl)oxamide, respectively). Compound 1 crystallizes in the triclinic system, space group PI, with a = 8.573(2), b = 12.808(3), c = 13.122(3) A, a = 99.63(3), β = 104.72(3) and y = 96.45(3)° at 299 K, Z= 2. The Cu(II) ions are in square-pyramidal surroundings and the Ni(II) ions in octahedral surroundings. The temperature dependence of the magnetic susceptibilities of 1 has been studied in the 5-300 K range, giving the exchange integral J = -92.7 cm - 1 . This value, while close to those reported for other Cu(II)-Ni(II) complexes involving Cu(oxpn), represents the minimum exchange constant of such heterobinuclear system.