Synthesis, crystal structure and magnetic property of a binuclear iron(III) citrate complex

The compound (Hql)(2)[Fe-2(cit)(2)(H2O)(2)]. 4H(2)O (1) [ql = quinoline, ci t(4-) = C(O-)(CO2-)(CH2CO2-)(2)], prepared by reacting ferric nitrate, sodi um citrate and quinoline in a molar ratio of 1:1:1 in aqueous solution, was characterized by density measurements, elementary analysis, i.r., X-ray cr ystallography and magnetic measurements. The X-ray crystallography results reveal that the molecule (1) consists of a binuclear iron(III) citrate anio nic complex [Fe-2(cit)(2)(H2O)(2)](2-) and two protonated quinolines [Hql]( +). The anionic complex has a centro-symmetric structure, in which two Fe3 ions are bridged by two mu (2)-alkoxo groups of the two deprotonated citra te ligands. The other coordination sites of the two slightly distorted octa hedra are completed by all the carboxylate groups of the two cit(4-) ligand s in a monodentate mode, and two coordinated water molecules. Magnetic meas urements indicate that the two Fe3+ ions are antiferromagnetically coupled below 200 K. A least-squares fit of variable-temperature (1.5-291 K) molar susceptibility data to a dimer model gave the coupling constant J/k = -6.35 (7) K and Lande factor g = 2.052(9), where the spin-only Heisenberg-Dirac-v an Vleck Hamiltonian is expressed as H = -2JS(1)S(2).