Synthesis, Characterization, and Magnetic Properties of Tetracarboxylato‐Bridged Binuclear Iron(II) Complexes

Abstract

Four new binuclear iron(II) complexes with a tetracarboxylato‐bridge have been synthesized and characterized, namely [Fe2(PMTA)L4], where L denotes 4,7‐diphenyl‐1,10‐phenanthroline (Ph2‐phen); 2,9‐dimethyl‐1,10‐phenanthroline (Me2phen); 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 (4–300 K) of the complexes [Fe2(PMTA)(Ph2phen)4] (1) and [Fe2(PMTA)(Me2phen)4] (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 Hamiltonian operator, Ĥ = −2JŜ 1 Ŝ 2, giving the exchange integrals J = −0.96 cm−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.