Molecular substitutional disorder in solid solutions of TTF-TCNQ and TSeF-TCNQ
Molecular substitutional order parameters were calculated for TTF1−xTSeFx-TCNQ ( x= 0, 0.5 and 1 ) at room temperature. A mean-field model was used in combination with the condition of thermodynamic stability. Intermolecular interactions were calculated in the atom-atom approximation.
It could be shown that the mutual substitution of TCNQ and TTF ( or TSeF ) Molecules is highly improbable in accordance to the x-ray structure determinations. On the other hand the TTF0.5TSeF0.5 stacks proved to be disordered completely concerning the mutual substitution of TTF and TSeF molecules. This conclusion supports the assumptions made implicitly by prior investigators. Finally it could be shown that the mixed crystal TTF0.5TSeF0.5-TCNQ is thermodynamically stable against decomposition into 0.5 TTF-TCNQ + 0.5 TSeF-TCNQ.
KeywordsLattice Energy Mutual Substitution Orientational Disorder Molecular Reorientation TCNQ Molecule
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