Phase Transitions in N-Propylpyridinium–TCNQ Ion-radical Complex Salts

Abstract

Abstract N-Propylpyridinium (TCNQ)x crystallized in two complex salts (x=2, 2.5), both of which displayed initial irreversible and subsequent reversible first-order phase transitions with a sharp discontinuity in the electrical conductivity. The reversible transitions of both salts are essentially the same in spite of their differences in stoichiometry. The transitions were accompanied by crystal structure changes; the changes in the physical properties were ascribed to the crystalline distortion in both the one-dimensional TCNQ chain and the motion of the cation molecules. The high-temperature phase was metallic, with a zero activation energy for conduction; the source of the metallic behavior was also discussed. The electronic and infrared absorption spectra suggest that the high-temperature modification has a less distorted stacking of TCNQ molecules in the column.