Synthesis and magnetic exchange interaction of μ-tetracarboxylato binuclear cobalt(II) complexes

Four new tetracarboxylato-bridged binuclear cobalt(II) complexes have been synthesized and characterized, namely [Co-2(PMTA)L-4], where L denotes 4,7-diphenyl-1,10-phenanthroline (Ph-2-phen); 2,9-dimethyl-1,10-phenanthroline (Me-2-phen); diaminoethane (en); 1,3-diaminopropane (pn) and PMTA represents the tetraanion of pyromellitic acid. Based on elemental analyses, molar conductivity measurements, spectroscopic (electronic and IR spectra) studies, it is proposed that these complexes have PMTA-bridged structures and consist of two cobalt(II) ions in a distorted octahedral environment. The complexes [Co-2(PMTA)(Ph-2-phen)(4)] (1) and [Co-2(PMTA)-(Me-2-phen)(4)] (2) were further characterized by variable temperature magnetic susceptibility measurements (4-300 K) and the observed data were successfully simulated by the equation based on the spin Hamiltonian operator, (H) over cap = -2J (S) over cap(1) . (S) over cap(2), giving the exchange integrals J = -0.48 cm(-1) for (1) and -0.41 cm(-1) for (2). The results indicate that there is a very weakly antiferromagnetic spin-exchange interaction between the two Co(II) ions within each molecule.