Descriptive analysis of the crystal structure of the 1-D semiconducting TCNQ salt : TEA(TCNQ)2, as a function of temperature. - I. Intermolecular distortions of the conducting TCNQ columns

Abstract

Within reasonable approximations, the structure of a conducting TCNQ column is characterized by six parameters. Two parameters define the equivalent regular column, and four parameters refer to the intermolecular distortions. Two of the distortional parameters are associated with a dimerization in the column, while the other two parameters are associated with a tetramerization. It is then shown, as an experimental fact, that only two of these six parameters are significantly temperature dependent. The first one simply accounts for the usual thermal expansion of the column. The second one is associated with a component of the tetramerization perpendicular to the column axis. The possible implications of these findings with respect to the semiconducting properties of the material are also discussed. In complement to the present article, a second one will concern an analysis of the charge distribution on the TCNQ molecules of a conducting column Il est montre qu'avec des approximations raisonnables, la structure d'une colonne conductrice de TCNQ peut etre caracterisee au moyen de six parametres, deux de ces parametres definissant la colonne reguliere equivalente et les quatre suivant se rapportant aux distorsions intermoleculaires. Deux des parametres de distorsion sont associes a une dimerisation de la colonne, et les deux autres a une tetramerisation. On fait ensuite apparaitre comme un fait experimental que seulement deux de ces six parametres varient d'une facon significative avec la temperature. Discussion des implications possibles de ces resultats sur les proprietes semiconductrices du materiau