Monotropic Phase Transition of the Complex Anion-Radical Salts of TCNQ with the N-(Methyl)quinolinium Cation

Abstract

Phase transitions were observed in various types of the complex salts of N-(methyl)quinolinium-7, 7, 8, 8-tetracyanoquinodimethan(MeQ–TCNQ). The specific resistivity increased irreversibly by a factor as high as 100 for crystals which included solvent molecules of crystallization and for those which were crystallized in a metastable form without any inclusion. Change in infrared spectra and powder X-ray patterns suggested that the latter crystal was monotropically transformed from a structure which is nearly isomorphous with that of quinolinium(TCNQ)₂ into a stable one which has distortions in linear chains of the stacks of the TCNQ molecules. The resistivity change of the inclusion compounds was caused by escape of the guest molecules which were thought to be originally situated in the channels between the TCNQ columns.