Crystal structures and magnetism of binuclear iron(III) complexes with a linear oxo-bridge, [Fe2O(bbimae)2X2][NO3]2{bbimae =2-[bis(benzimidazol-2-ylmethyl)amino]ethanol, X = Cl or NCS}

Abstract

The crystal structures of the oxo-bridged binuclear iron(III) complexes [Fe₂O(bbimae)₂X₂][NO₃]₂{X = Cl (1) or NCS (2); bbimae = 2-[bis(benzimidazol-2-ylmethyl)amino]ethanol} have been determined by X-ray diffraction methods. Crystals of (1) are monoclinic with a=11.949(3), b=15.901(4), c= 11.326(2)Å, β=109.36(2)°, space group P2₁/n, and Z= 2. Crystals of (2) are orthorhombic with a=16.384(2), b=19.804(2), c=13.600(2)Å, space group Pbca, and Z= 4. Both crystals are composed of centrosymmetric dimeric cations with a linear Fe–O–Fe bond and nitrate counter ions. The iron–iron and iron–oxo distances are 3.563(1) and 1.7816(7)Å for (1) and 3.559(1) and 1.7795(8)Å for (2). Mossbauer spectra reveal the presence of high-spin iron(III) atoms in both complexes. The magnetic moments of 1.81(295 K) and 0.73 B.M. (98 K) for (1) and 1.82 (295 K) and 0.89 B.M. (98 K) for (2) indicate an antiferromagnetic interaction between the two iron(III) atoms. The –J value was evaluated as 103 cm^–1 for (1), which falls in the range (95–110 cm^–1) of previously reported oxo-bridged complexes with Fe–O–Fe bond angles in the range 139–180°