J. Phys. IV France
Volume 12, Numéro 9, November 2002
Page(s) 145 - 148

J. Phys. IV France
12 (2002) Pr9-145
DOI: 10.1051/jp4:20020381

X-ray observation of 2 $k_{\rm F}$ and 4 $k_{\rm F}$ charge orderings in (TMTTF) 2Re0 4 and (TMTTF) 2SCN associated with anion orderings

Y. Nogami1 and T. Nakamura2

1  Depattment of Physics, Okayama University, 3-1-1 Tsushimanaka, Okayama 700-8530, Japan
2  Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan

Electronic transfer integrals ( t) and TMTTF molecular ionicities (p) in several Fabre salts were estimated using the atomic coordinates obtained by systematic X-ray structure analyses at room and low temperatures. Among these Fabre salts containing the octahedal anions, (TMTTF) 2PF 6 has the largest degree of 4 $k_{\rm F}$ bond dimerization in t, (TMTTF) 2AsF 6, does the middle and (TMTTF) 2SbF 6 has the smallest. This tendency correspondr well to the degree of 2 $k_{\rm F}$ spin-Peierls instability at low temperatures which had been estimated. However opposite tendency was observed between the magnitude of the 4 $k_{\rm F}$, bond dimerization and the reported critical temperature of the charge disproportionation. The charge mochlation patterns and the transfer integral modulation patterns of two salts containing non centrosymmetric anions, (TMTTF) 2ReO 4 and (TMlTF) 2SCN were compared.

© EDP Sciences 2002