DEPENDENCE OF THE RATE OF INTRAMOLECULAR ELECTRON-TRANSFER ON CRYSTALFORM IN MIXED-VALENCE TRINUCLEAR IRON PHENYLACETATE COMPLEX

A dependence of the rate of intramolecular electron transfer on crysta l form in mixed-valence trinuclear iron phenylacetate, [(Fe2FeO)-Fe-II I-O-II(O(2)CCH(2)Ph)(6)(py)(3)] (py = pyridine), was found. This compl ex was obtained in two different crystal forms : a columnar and a need le crystal form. Mossbauer spectra of the columnar crystals showed a t emperature-dependent valence detrapping, whereas the needle crystals s howed a trapped mixed-valence state from a lower temperature up to roo m temperature. The structure of the columnar crystal was determined by single-crystal X-ray diffraction. The complex is located on the C-2 a xis passing through central O-Fe; thus, there are two crystallography inequivalent iron sites. The Fe-Fe distances are 3.305(1) and 3.311(1) Angstrom, in agreement with their being indistinguishable on the Fe-5 7 Mossbauer time-scale (similar to 10(-7)-10(-8) s). There is no evide nce indicating intermolecular pi-pi interactions through the phenyl gr oups and/or pyridine ligands.