Pronounced effects of crystal structures on intramolecular electron transfer in mixed-valence biferrocenium cations: Structural, EPR, and Fe-57 Mossbauer characteristics

摘要

Crystallographic properties play an important role in controlling the rate of electron transfer in mixed-valence 1', 1'''-disubstituted-biferrocenium triiodide salts. The X-ray structure of neutral 1',1'''-dinaphthylmethylbiferrocene has been determined at 298 K, The corresponding mixed-valence 1', 1'''-dinaphthylmethylbiferrocenium triiodide exhibits two crystalline morphologies at 298 K, Dark crystals, formed when a CH2Cl2 solution of triiodide salt was allowed to evaporate slowly, crystallize in space group . Dark crystals, obtained when a layer of hexane was allowed to slowly diffuse into a CH2Cl2 solution of triiodide salt, crystallize in monoclinic space group P2(1). The observations of the structural characteristics of 1',1'''-dinaphthylmethylbiferrocenium triiodide are also consistent with our Mossbauer studies, The cation with space group shows two doublets in the variable-temperature Mossbauer spectra at temperatures below 100 X. An increase of temperature causes the two doublets to move together, resulting in an average-valence doublet at 130 K. at 300 K:, the spectrum of this sample shows a single doublet which is characteristic of a valence-detrapped cation in which the electron-transfer rate exceeds similar to 10(8) s(-1). On the other hand, the cation with P2(1) phase exhibits a Mossbauer spectrum characteric of a valence-trapped cation at 300 K. Obviously, the intramolecular electron-transfer rate is quite sensitive to environment perturbations caused by different crystal packing arrangements. At 77 K, the EPR spectrum of cation with phase is clearly a typical axial-type spectrum with g(parallel to) = 3.16 and g(perpendicular to) 1.91. Surprisingly, the EPR spectrum of the cation with P2(1) phase consists of two g(parallel to) signals (3,67 and 2.85) and two g(perpendicular to) signals (2.01 and 1..79). We suggest that, the origin arises from the interaction of spin-spin exchange resulting from a dipole-dipole interaction that develops between cations,The syntheses, characterizations, and physical properties of mixed-valence 1',1'''-di(4-biphenylmethyl)biferrocenium and 1',1'''-di(9-anthracenylmethyl) beferrocenium triiodide salts are also described. [References: 46]