Dinuclear and tetranuclear iron(III) complexes containing the μ-oxo-di-μ-acetato motif

A series of μ-oxo-di-μ-acetato-bridged diiron(III) and tetrairon(III) complexes are reported. The remainder of the Fe coordination spheres are occupied by the ligands N-methyl-bis(2-pyridylmethyl)amine (medpa), N-methyl-N,N,N′,N′-tetrakis(2-pyridylmethyl)-1,2-ethanediamine (metpen+), N,N,N′,N′-tetrakis(2-pyridylmethyl)-1,3-propanediamine (tptn) and N,N,N′,N′-tetrakis(2-pyridylmethyl)-1,4-butanediamine (tpbn). The crystal structures of two new μ-oxo-di-μ-acetato-brigded diiron(III) complexes, [Fe2medpa2(CH3CO2)2O]-(ClO4·2H2O (1) and [Fe2metpen2(CH3CO2)2O](ClO4)4·7H2O (2) have been determined. They have identical core characteristics to a tetranuclear iron(III) reported in an earlier communication. Complex 1 crystallizes in the monoclinic space group P21/c, with a = 10.753(3), b = 23.990(3), c = 16.291(1) A , β = 108.40(1) and Z = 4 . The structure refined to a final R value of 0.101 for 4050 reflections. The Fe atoms are bridged by a μ-oxo group and two acetate groups with Fe-μ-O, 1.816(9), 1.76(1) A; FeOFe, 118.2(4)°; and Fe…Fe 3.068(3) A. Complex 2, which contains an unusual positively-charged ligand crystallizes in the orthorhombic space group Cmcm, with a = 15.895(4), b = 29.754(9), c = 16.254(5) A and Z = 4 . The structure refined to afinal R value of 0.066 for 1399 reflections. The Fe atoms are bridged by a μ-oxo group and two acetate groups with Fe-μ-O, 1.800(6) A; FeOFe, 116.4°; and Fe…Fe 3.059(4) A. By contrast, the complexes of tptn and tpbn form tetranuclear complexes with the propane and butane backbones ‘strapping’ between two [FeO(CH3CO2)2Fe] cores.