ESR studies of the alkali metal salts of the anion radicals of tetracyanoquinodimethan (TCNQ) and tetrafluorotetracyanoquinodimethan (TCNQF4) in dilute solutions of ether type solvents reveal that solutions of salts of both anion radicals are ion paired. Quantitative measurements of the values of the hyperfine splittings (hfs) as a function of temperature for these salts in solution show that the isotropic hfs are temperature and solvent dependent. In contrast, the observed isotropic g-value for a given salt of either anion radical in solutions of the solvents studied is independent of temperature and solvent. However, there is a weak dependence of the isotropic g-value upon the alkali metal ion in the case of the heavier alkali metal ion salts, i.e., Cs/TCNQ, Rb/TCNQF4, and Cs/TCNQF4. The studies reported here (1) re-enforce an earlier report of ion pairing in solutions of the potassium salts of TCNQ and TCNQF4, (2) establish that ion pair formation occurs in the entire alkali metal TCNQ and TCNQF4 salt series in ether type solvents based on temperature and solvent dependent hyperfine splittings, and (3) present observations of phenomena indicative of ion pairing not seen in these systems in previous studies (i.e., the dependence of the isotropic g-value upon the identity of the alkali metal ion for the heavier alkali metal ions).
