Two oxo complexes with tetra-nuclear [Fe4(μ3-O)2]8+ and trinuclear [Fe3(μ3-O]7+ units

Two new oxo complexes, namely hexa-mu(2)-acetato-acetato-aquabis(di-3-pyridylamine)di-mu(3)-oxo-tetrairon(III) chloride monohydrate ethanol 1.25-solvate, [Fe-4(C2H3O2)(7)O-2(C10H9N3) (2)(H2O)]Cl center dot 1.25C(2)H(6)O center dot H2O, (I), containing a tetranuclear [Fe-4(mu(3)-O)(2)](8+) unit, and 2-methylimidazolium hexa-mu(2)-acetato-acetatodiaqua-mu(3)-oxo-triiron(III) chloride dihydrate, (C4H7N2)[Fe-3(C2H3O2)(7)O(H2O)(2)]Cl center dot 2H(2)O, (II), with a trinuclear [Fe-3(mu(3)-O)](7+) unit, are presented. Both structures are formed by two well differentiated entities, viz. a compact isolated cluster composed of Fe III ions coordinated to O2- and CH3CO2- anions, and an external group formed by a central Cl. ion surrounded by different solvent groups to which the anion is bound through hydrogen bonding. In the case of ( I), charge balance cannot be achieved within the groups, so the structure is macroscopically ionic; in the case of (II), in contrast, each group is locally neutral owing to the internal compensation of charges. The trinuclear complex crystallizes with the metal cluster, chloride anion and 2-methylimidazolium cation bisected by a crystallographic mirror plane.