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

A series of mu-oxo-di-mu-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-ethane-diamine (metpen(+)), N,N,N',N'-tetrakis(2-pyridylmethyl)-1,3-(tptn) and N,N,N',N'-tetrakis(2-pyridylmethyl)-1, 4-butanediamine (tpbn). The crystal structures of two new mu-oxo-di-mu-acetato-brigded diiron(III) complexes, [Fe(2)medpa(2)(CH3CO2)(2)O]-(CIO4)(2) . 2H(2)O (1) and [Fe(2)metpen(2)(CH3CO2)(2)O](CIO4)(4) . 7H(2)O (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 P2(1)/c, with a = 10.753(3), b = 23.990(3), c = 16.291(1) Angstrom, beta = 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 mu-oxo group and two acetate groups with Fe-mu-O, 1.816(9), 1.76(1) Angstrom; Fe-O-Fe, 118.2(4)degrees; and Fe...Fe 3.068(3) Angstrom. 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) Angstrom and Z = 4. The structure refined to a final R value of 0.066 for 1399 reflections. The Fe atoms are bridged by a mu-oxo group and two acetate groups with Fe-mu-O, 1.800(6) Angstrom; Fe-O-Fe, 116.4 degrees; and Fe...Fe 3.059(4) Angstrom. By contrast, the complexes of tptn and tpbn form tetranuclear complexes with the propane and butane backbones 'strapping' between two [FeO(CH3CO2)(2)Fe] cores.