Effect of Cesium Counterion on the ESR Spectrum of Tetracyanoethylene Anion Radicals

Abstract

Abstract Evidence was obtained by ESR for the ion-pair formation between the tetracyanoethylene anion radical and the cesium counterion in tetrahydrofuran. The hyperfine lines of the ESR spectrum of cesium tetracyanoethylenide were exceptionally broad at high salt concentrations in tetrahydrofuran, while they were remarkably narrowed by the addition of a small amount of DMF or triglyme (cation-solvating agents) or by replacing the counterion with the tetra-n-butylammonium ion. This indicates that the broad linewidth is due to the unresolved hyperfine splitting of the cesium counterion. In addition, the concentration dependence of the ESR spectrum indicates that the line broadening is to be interpreted not only in terms of the Heisenberg spin exchange, but also in terms of the equilibrium between the ion-pair and the free ion. The cesium hyperfine coupling constant was estimated by simulating the line shape to be 40 m Gauss in the ion-pair state between the tetracyanoethylene anion radical and the cesium ion in the tetrahydrofuran solution.