BINUCLEAR IRON(III) COMPLEXES BRIDGED BY TEREPHTHALATO GROUPS

Six new mu-terephthalato iron(III) binuclear complexes have been prepa red and identified: [Fe-2(TPHA)(L)(4)](ClO4)(4), [L = 2, 2'-bipridine (bpy); 1,10-phenanthroline (phen); 4,4'-dimethyl-2,2'-bipyridine (Me(2 )bpy); 5-methyl-1,10-phenanthroline (Me-phen); 5-chloro-1,10-phenanthr oline (Cl-phen) and 5-nitro-1,10-phenanthroline (NO2-phen)]; where TPH A = 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 f or these complexes. The [Fe-2(TPHA)(Me-phen)(4)](ClO4)(4) (1) and [Fe- 2(TPHA)(phen)(4)](ClO4)(4) (2) complexes were characterized by variabl e temperature magnetic susceptibility (4-300 K) measurements and the o bserved 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 = -1.05 cm(-1) for (1) and J = -9.28 cm(-1) for (2). This result indicates the presence of a weak an tiferromagnetic spin-exchange interaction between the metal ions withi n each molecule. The influence of the terminal ligand methyl substitue nts on magnetic interactions between the metals is also discussed.