Synthesis and antiferromagnetic interaction in tetrabromoterephthalato-bridged binuclear iron(II) complexes

Five new binuclear iron(II) complexes have been synthesized and characterized, namely: [Fe-2(BTPHA)L-4] (ClO4)(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) and 5-methyl-1,10-phenanthroline (Me-phen), respectively, and BTPHA represents the tetrabromoterephthalale dianion. Based on the elemental analyses, molar conductance measurements, and spectroscopic studies, extended BTPHA-bridged structures consisting of two iron(II) ions, each in an octahedral environment are proposed for these complexes. The variable temperature magnetic susceptibilities (4 similar to 300 K) for [Fe-2(BTPHA)(Me-2-bpy)(4)](ClO4)(2) (1) and [Fe-2(BTPHA)(Me-2-phen)(4)](ClO4)(2) (2) complexes were measured 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 = -1.09 cm(-1) for (1) and J = -2.13 cm(-1) for (2). These results indicate the presence of a weak antiferromagnetic spin-exchange interaction between the metal ions within each molecule. The influence of the bromo substituents in the bridge ligand on the magnetic interactions between the metal ions in this kind of complexes is also discussed.