SYNTHESIS, CHARACTERIZATION AND MAGNETISM OF TETRACARBOXYLATO-BRIDGEDDINUCLEAR NICKEL(II) COMPLEXES

Five new tetracarboxylato-bridged dinuclear nickel(II) complexes of th e formula [Ni-2(PMTA)L-4], where L denotes 4,7-diphenyl-1,10-phenanthr oline (Ph-2-phen); 2,9-dimethyl-1, 10-phenanthroline (Me-2-phen); diam inoethane (en); 1,3-diaminopropane (pn) and 1,2-diaminopropane (ap); a nd PMTA represents the tetraanion of pyromellitic acid, have been synt hesized and characterized by elemental analyses, molar conductivity an d room temperature magnetic moment measurements, and by spectroscopy. It is proposed that these complexes have PMTA-bridged structures and c onsist of two nickel(II) ions in a distorted octahedral environment. T he complexes [Ni2(PMTA)(Ph-2-phen)(4)] (1) and [Ni-2(PMTA)(Me-2-p]len) (4)] (2) were further characterized by variable temperature magnetic s usceptibility measurements (4-300 K) and the observed data were treate d in terms of two theoretical models, giving the exchange integrals J = -2.85 cm(-1) for (1) and -1.96 cm(-1) for (2), The result indicates that there is a very weakly antiferromagnetic spin-exchange interactio n between two the NI(II) ions within each molecule.