J. Phys. I France
Volume 4, Numéro 10, October 1994
Page(s) 1479 - 1490
DOI: 10.1051/jp1:1994202
J. Phys. I France 4 (1994) 1479-1490

Concerning the first-order transition in the $\kappa$-phase (BEDT-TTF) 4PtCl 6 $\cdot$ C 6H 5CN

Marie-Liesse Doublet1, Enric Canadell1 and Rimma P. Shibaeva2

1  Laboratoire de Chimie Théorique, Université de Paris-Sud, 91405 Orsay Cedex, France
2  Institute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow District, Russia

(Received 19 May 1994, accepted 4 July 1994)

(BEDT-TTF) 4PtCl 6 $\cdot$ C 6H 5CN is a $\kappa$-phase exhibiting a first-order transition at 250 K. The crystal structure of this salt contains two different donor layers before the transition but only one after the transition. Every layer contains two different BEDT-TTF donor molecules. Our tight binding band structure study suggests that this is the first BEDT-TTF salt containing BEDT-TTF in three different oxidation states (0, + 1/2 and + 1). One of the layers ( ${\cal A}$) contains [ BEDT-TTF +1] 2 and [ BEDT-TTF 0] 2 dimers whereas the other layer ( ${\cal B}$) contains two different [ BEDT-TTF +1/2] 2 dimers. We suggest that the first-order transition is associated with the disproportionation of the two [ BEDT-TTF +1/2] 2 dimers of layer ${\cal B}$ in [ BEDT-TTF +1] 2 and [ BEDT-TTF 0] 2 dimers. This process is associated with a conformational change in one of the dimers which apparently optimizes the donor-acceptor interactions in this $\kappa$-phase. According to the present results it would be worthwhile to reexamine the transport properties of this salt.

© Les Editions de Physique 1994