Mixed-Valence States of Orthorhombic [Fe3O(C6F5COO)6(C5H5N)3]·CH2Cl2 Characterized by X-ray Crystallography and 57Fe Mössbauer Spectroscopy: Comparison with a Hexagonal Polymorph

An orthorhombic form of polymorphs of mixed-valence trinuclear iron pentafluorobenzoate containing dichloromethane as a crystal solvent molecule, [Fe3O(C6F5COO)6(C5H5N)3]·CH2Cl2 (o-1), was newly prepared and confirmed by single crystal X-ray analysis at 123 and 300 K. Three bond lengths of Fe–O in the central Fe3O moiety are not identical, which is in contrast to our previously reported hexagonal form (h-1) having D3h local symmetry.1 57Fe Mossbauer spectra of o-1 showed a valence-trapped state consisting of high-spin Fe(III) and high-spin Fe(II) atoms with an area ratio of 2/1 to 3/1 between 78 and 300 K, being in complete contrast to those of h-1 with the valence-detrapped (averaged) state above ∼90 K. The present findings are consistently explained from the viewpoints of the crystal and molecular structures.