The charge transfer in some alkaline salts of tetracyanoquinodimethane (TCNQ): A Zeeman perturbation study of the 14N nuclear quadrupole resonance spectrum of polycrystalline Rb–TCNQ

Two 14N nuclear quadrupole resonance absorption lines (2904.4 and 2967.7 kHz) detected in Rb–tetracyanoquinodimethane (TCNQ) at room temperature were studied by the Zeeman perturbation effect and the results interpreted in terms of the theory of Pissanetzky [J. Chem. Phys. 59, 4197 (1973)]. The two lines were identified as ν+ with η of 0.40±0.04 and 0.57±0.05 and coupling constants of 3490 and 3254 kHz, respectively. The observed spectrum is compatible with a crystal structure with two inequivalent nitrogen sites such as the monoclinic phase of Rb–TCNQ II. Using the Townes and Dailey theory and an estimation of the effects of the crystal field, and by comparison of the NQR data of K, Rb, and neutral TCNQ, we found an increase of about 10% to 14% in the πx population and a decrease of about 5% in the σ population at the nitrogen. A two-way charge transfer within the CN group seems to take place upon the molecular charge transfer as predicted by Clementi and Klint [J. Chem. Phys. 50, 4899 (1969)].