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

Four new binuclear iron(II) complexes with a tetracarboxylato-bridge have been synthesized and characterized, namely [Fe-2(PMTA)L-4], where L denotes 4,7-diphenyl-1,10-phenanthroline (Ph-2-phen); 2,9-dimethyl- 1, 10-phenanthroline (Me,phen): diaminoethane (en); 1.3-diaminopropane (pn) and PMTA represents the tetraanion of pyromellitic acid. Based on elemental analyses, magnetic moments at room-temperature and molar conductivity measurements, spectroscopic (electronic and IR spectra) studies, it is proposed that these complexes have PMTA-bridged structures and consist of two iron(II) ions in a distorted octahedral environment. The variable-temperature magnetic susceptibilities (4-300K) of the complexes [Fe-2(PMTA)(Ph(2)phen)(4)] (1) and [Fe-2, (PMTA)(Me,phen)41 (2) were measured. and studied in detail. The magnetic analysis was carried out by means of a least-square method to the observed data with the Susceptibility equation derived from the spin Hamillonian operator, (H) over cap = -2J (S) over cap (1)(S) over cap (2), giving the exchange integrals J = -0.96cm(-1) for (1) and J = -0.85 cm(-1) for (2). The results indicate that there is a very weak antiferromagnetic spin-exchange interaction between the two Fe(II) ions within each molecule.