Even-Odd Character and Dynamic Electronic State in the Binuclear Ferrocene Derivatives with Long Alkyl Substituents Satoru Nakashima,* ,† Shinsuke Nakazaki, ‡ Hiroshi Sakai, § Masanobu Watanabe, | Izumi Motoyama, | and Masaru Sato ⊥ Radioisotope Center and Department of Chemistry, Faculty of Science, Hiroshima University, Kagamiyama, Higashi-Hiroshima 739-8526, Japan, Department of Chemistry, Faculty of Science, Konan University, Higashi-Nada, Kobe 658-8501, Japan, Department of Chemistry, Faculty of Engineering, Kanagawa University, Rokkakubashi, Yokohama 221-8686, Japan, and Chemical Analysis Center, Saitama University, Urawa, Saitama 338-8570, Japan ReceiVed September 18, 1997 X-ray powder diffraction patterns revealed that 1′,1′′′-diheptyl- and 1′,1′′′-dioctyl-1,1′′-biferrocenium triiodides obtained from hexane and from dichloromethane have a layered structure with longer interlayer distances. 1′,1′′′- Diheptyl-1,1′′-biferrocenium triiodide falls under the category reported before, while 1′,1′′′-dioctyl-1,1′′- biferrocenium triiodide becomes exception; it shows a valence detrapping with increasing temperature despite the longer interlayer series. The difference in the crystal structure between longer and shorter interlayer distance series was reflected in the difference of the space group. 1′,1′′′-Diheptyl-1,1′′-biferrocenium triiodide (C 34 H 46 - Fe 2 I 3 ) crystallizes in the monoclinic space group P2 1 /c with unit cell parameters a ) 27.209(10) Å, b ) 9.6480- (6) Å, c ) 14.042(10) Å,  ) 98.572(4)°, and Z ) 4, while 1′,1′′′-dioctyl-1,1′′-biferrocenium triiodide (C 36 H 50 Fe 2 I 3 ) crystallizes in the monoclinic space group P2 1 /c with a ) 20.758(6) Å, b ) 9.80(1) Å, c ) 37.88(2) Å,  ) 90.44(3)°, and Z ) 8. Both salts in the present study have a space group of P2 1 /c, which is different from the shorter interlayer series; 1′,1′′′-dihexyl- and 1′,1′′′-didodecyl-1,1′′-biferrocenium triiodides have a space group of P1 h. The difference in the structure between the 1′,1′′′-diheptyl derivative and the 1′,1′′′-dioctyl derivative is also discussed. There is a difference in the symmetry of the monocation between the two salts, while both show the unsymmetrical triiodide anion. The difference between them makes the difference of the cation-cation interaction. The structure of the cations agrees with the result of 57 Fe Mo ¨ssbauer spectroscopy. The cation-cation interaction in the stacking is observed in 1′,1′′′-dioctyl derivative, while such interaction is disturbed by the adjacent stacking in 1′,1′′′-diheptyl derivative. 1. Introduction The nature of electron transfer between well-separated metal sites has been discussed in connection with studies of super- conductive materials and biological systems. 1,2 D. O. Cowan and F. Kaufman provided us with mixed-valence states of binuclear ferrocenes. 3 Recently, M. Watanabe et al. found an interesting mixed-valence state in binuclear ruthenocenes. 4 The mixed-valence binuclear ferrocene derivatives are recognized as a good model compound in studying the intramolecular electron-transfer process because of the ease of synthetic design and of various selectivities for counteranions. Recent progress of understanding of the mixed-valence state for binuclear ferrocene derivatives is due to the discovery of a temperature- dependent mixed-valence state in 1′,1′′′-diethyl-1,1′′-biferroce- nium triiodide, in which two quadrupole-split doublets observed at low temperatures converge into one doublet and no significant broadening of the half-width in 57 Fe Mo ¨ssbauer spectra is observed in the detrapping process. 5 Hendrickson’s and Sano’s groups suggested the important role of environment in the mixed-valence state. 2,6,7 For a long time, the present authors have studied the mixed- valence state of binuclear ferrocene derivatives, especially by means of 57 Fe Mo ¨ssbauer spectroscopy and X-ray structural analyses, in order to clarify the important role of environment in the mixed-valence state. 8-11 Recently, our attention has been concentrated on the triiodide salts of binuclear ferrocenes with long alkyl substituents, exhibiting layered structures. Those structures are divided into two groups: one has longer interlayer distances and the other has shorter interlayer distances. Sys- tematic change of the alkyl group showed an interesting even- odd character in the relationship between the interlayer distance and the number of carbon atoms of the substituent. 12-17 That is, the salts with odd-numbered carbons in the alkyl substituent * To whom all correspondence should be addressed. † Radioisotope Center, Hiroshima University. ‡ Department of Chemistry, Hiroshima University. § Konan University. | Kanagawa University. ⊥ Saitama University. (1) Mixed-Valence Compounds: Theory and Applications in Chemistry, Physics, Geology, and Biology; Brown, D. B., Ed.; D. Reidel Publishing Company: Dordrecht, 1980. (2) Mixed Valency Systems: Applications in Chemistry, Physics, and Biology; Prassides, K., Ed.; Kluwer Academic Publishers: Dordrecht, 1991. (3) Cowan, D. O.; Kaufman, F. J. Am. Chem. Soc. 1970, 92, 219. (4) Watanabe, M.; Motoyama, I.; Takayama, T. J. Organomet. Chem. 1996, 523, 153. (5) Iijima, S.; Saida, R.; Motoyama, I.; Sano, H. Bull. Chem. Soc. Jpn. 1981, 54, 1375. (6) Sano, H. Hyperfine Interact. 1990, 53, 97. (7) Dong, T.-Y.; Hendrickson, D. N.; Iwai, K.; Cohn, M. J.; Geib, S. J.; Rheingold, A. L.; Sano, H.; Motoyama, I.; Nakashima, S. J. Am. Chem. Soc. 1985, 107, 7996. 1959 Inorg. Chem. 1998, 37, 1959-1966 S0020-1669(97)01179-8 CCC: $15.00 © 1998 American Chemical Society Published on Web 04/03/1998