Synthesis, characterization and magnetic properties of tetracarboxylato-bridged binuclear cobalt(II) complexes

Four new cobalt(II) binuclear complexes, described by the overall formula [ Co-2(PMTA)L-4], where L denotes 4,4'-dimethyl-2,2'-bipyridine (Me-2-bpy); 5 -methyl-1,10-phenanthroline (Me-phen); 5-chloro-1,10-phenanthroline (Cl-phe n); 5-bromo-1,10-phenanthroline (Br-phen) and PMTA represents the tetraanio n of pyromellitic acid, have been synthesized and characterized by elementa l analyses, molar conductivity measurements and spectroscopic (electronic a nd IR spectra) studies. It is proposed that these complexes have PMTA-bridg ed structures and consist of two cobalt(II) ions, each in a distorted octah edral environment. The complexes [Co-2(PMTA)(Me-2-bpy)(4)] (1) and [Co-2(PM TA)(Me-phen)(4)] (2) were further characterized by variable temperature mag netic susceptibility measurements (4-300 K) and the observed data were succ essfully 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 p arameters J = -1.16 cm(-1) for (1) and -1.21 cm(-1) for (2), The result ind icates that there is a very weak antiferromagnetic spin-exchange interactio n between the two Co(II) ions within each molecule.