Synthesis and magnetism of binuclear iron(II) complexes bridged by terephthalato dianions

Four new telephthalato-bridged iron(II) binuclear complexes of the formula [Fe-2(TPHA)L-4](CIO4)2, where L stands for 4,4'-dimethyl-2,2'-bipyridine (Me(2)bpy); 2,9-dimethyl-1,10-phenanthroline (Me(2)phen); 5-bromo-1,10-phenanthroline (Br-phen); 5-chloro-1,10-phenanthroline (Cl-phen), respectively, and TPHA represents the terephthalate dianion, have been synthesized and characterized. Based on the elemental analyses, molar conductance and magnetic moments of room-temperature measurements, and spectroscopic studies, extended TPHA-bridged structures consisting of two iron(II) ions, each in an octahedral environment are proposed for these complexes. The [Fe-2(TPHA)(Me(2)bpy)(4)](ClO4)(2) (1) and [Fe-2(TPHA)(Me(2)phen)(4)](ClO4)(2) (2) complexes were characterized by variable temperature magnetic susceptibility (4 similar to 300 K) measurements 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 = -2.15 cm(-1) for (1) and J = -3.28 cm(-1) for (2). This result indicates the presence of a weak antiferromagnetic spin-exchange interaction between the metal ions within each molecule.