Binuclear iron(III) complexes bridged by terephthalato groups

Six new μ-terephthalato iron(III) binuclear complexes have been prepared and identified: [Fe2(TPHA)(L)4]-(ClO4)4 [L = 2,2′-bipyridine (bpy); 1,10-phenanthroline (phen); 4,4′-dimethyl-2,2′-bipyridine (Me2bpy); 5-methyl-1,10-phenanthroline (Me-phen); 5-chloro-1,10-phenanthroline (Cl-phen) and 5-nitro-1,10-phenanthroline (NO2-phen)]; where TPHA = the terephthalate dianion. 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(III) ions, each in an octahedral environment, are proposed for these complexes. The [Fe2(TPHA)(Me-phen)4](ClO4)4(1) and [Fe2(TPHA)(phen)4](ClO4)4(2) complexes were characterized by variable temperature magnetic susceptibility (4–300 K) measurements and the observed data were successfully simulated by the equation based on the spin Hamiltonian operator, Ĥ = −2JŜ1Ŝ2, giving the exchange integrals J = −1.05 cm−1 for (1) and J = −9.28 cm−1 for (2). This result indicates the presence of a weak antiferromagnetic spin-exchange interaction between the metal ions within each molecule. The influence of the terminal ligand methyl substituents on magnetic interactions between the metals is also discussed.