Transfer Integrals for TCNQ Salts

Abstract

Résumé -Les intégralesde transfert sont de grande importance pour la compréhension des propriétés physiques des sels de TCNQ, particulièrement parce que leurs structures cristallographiques varient considérablement. Cette note donne une méthode sûre pour leur calcul.Abstract -Transfer integrals are of prime importance in understanding the physical properties of TCNQ-salts, particularly since the crystal structures vary widely. This paper gives a reliable method of their calculation. IntroductionFor a fairly long time it has been known that the properties of TCNQ-salts vary widely. Depending on whether one considers 1:1 or 1:2 salts, insulators and metals have been found, 4kF and 2kF phase transitions occur and many different crystal structures have been determined even of chemically very similar compounds. As a case in point we may take the derivatives of R1R2-morpholinium-(TCNQ)2, where R1 and R2 may be varied (note elsewhere in these proceedings the papers of De Boer et al. and Oostra et al. for a review of crystal structures and physical properties.

Descriptive analysis of the crystal structure of the 1-D semiconducting TCNQ salt : TEA(TCNQ)2, as a function of temperature. - II. Charge distribution on the conducting TCNQ columns

“…This simplified linear function is shown in figure 3, as line b. A further step in the present analysis proceeds from the results by the Groningen group, already mentioned in section 1, of a transfer integral calculation applied to-the case of TEA(TCNQ)2 [8]. According to these results, the intradimer transfer integral t is a decreasing function of temperature, closely reproduced above 100 K (and below 350 K) by the linear equation :…”

“…From crystallographic considerations [1,2], the tetramerization of the columns clearly persists at the highest temperatures, probably up to the crystal decomposition. On the other hand, recent transfer integral calculations [8] suggest that, whereas dimerization is always present, tetramerization could become insignificant above 300 K, from a purely electronical point of view.…”

Structural evolution of the one-dimensional organic conductor triethylammonium–7,7,8,8-tetracyano-p-quinodimethane (1:2) [TEA–(TCNQ)2] in the temperature range 40 to 345 K

“…Our data in Table 6 have been used by Janssen, Visser, Jonkman, de Boer & Kommandeur (1983) to compute the transfer integrals in TEA-(TCNQ)2 as a function of T. From the whole data set in Table 7 we concluded (see Results, § iv) that there is no very significant change, with temperature, of the charge transfer onto TCNQA and TCNQ~ species. However, Farges (1983a) recently noted that according to our own structure refinements a change, linear with T, of the charge distribution is apparent with characteristic values 0.5 and 0.5 e at T oo, and 0 and 1 e at T-48 K. Finally we wish to note here that, based on our present results, Farges (1983 b) gave a complementary analysis of the TCNQ chain behaviour, and for example noted that the structure change with T is mainly a transverse shift of dimers which are the stable part of the stacks.…”

Temperature Study of the Polarized Reflectivity of TEA(TCNQ)2Single Crystal

“…The interplanar distances between TCNQs (3.225 Å and 3.12 at T = 300 K and 80 K, respectively) and numbers of dimers per A3 (0.001449 and 0.001504, at both temperatures, respectively) were found from the structural data [4]. The transfer integrals t = 151 meV (at 300 K) and t = 198 meV (at 80 K), calculated according to [33], were used for the dimer fit to the experimental spectra at both temperatures. Fitting was made using the Nelder-Mead simplex algorithm for minimizing a nonlinear function of several variables.…”