Electronic Spectra of Crystalline TCNQ Anion Radical Salts. I. Simple Salts

Abstract The present paper deals with crystalline TCNQ, anion radical “simple” salts of M+ TCNQ, where M+ represents a diamagnetic counter cation. Their crystalline electronic spectra were measured in the range between 4. 0 and 30. 8 kK by means of diffuse reflectance. The crystalline spectra thus obtained were quite different from that of the TCNQ, radical anion monomer and exhibited a broad and intense low-energy band around 9 kK in the low-conductivity compounds and at 4. 3 kK in the high-conductivity compound. These bands were ascribed to inter-radical charge-transfer in the solid state. The crystalline spectra were found to be closely correlated to their unusual electrical and magnetic properties. It was concluded that these physical properties were based on a unique TCNQ molecular arrangement in groups of several or an infinite number of face-to-face molecular systems.