Infrared spectroscopic study of electrically conducting tetracyanoquinodimethane salts of copper chelates with ethylenediamine

Abstract

The infrared spectra of Cu(en)(TCNQ)₂ and Cu(en)₂(TCNQ)₂(en: ethylenediamine, TCNQ: 7,7,8,8-tetracyanoquinodimethane) have been shown to exhibit totally symmetric TCNQ A_g bands activated by a vibronic process in addition to inherently i.r.-active B_u bands. In the spectrum of Cu(en)₂(TCNQ)₃ some A_g modes were developed as sharp indentations in a very broad electronic absorption envelope which had a steep edge at 1100 cm^–1. The assignment of the i.r. spectra was made by comparing them with those of Cu(TCNQ) and Cu(TCNQ)₂. The results indicate the following formal charge distributions of the compounds in accordance with magnetic data: Cu⁺(TCNQ^–), Cu⁺(TCNQ^–)(TCNQ⁰), Cu⁺(en)(TCNQ^–)(TCNQ⁰), Cu²⁺(en)₂(TCNQ^–)₂ and Cu²⁺(en)₂[(TCNQ)₃]^2–. The electrical properties, especially the thermoelectric power, of each compound were explained consistently by taking into account a solid-state equilibrium on the basis of the corresponding formula described above.