Comparative ESR studies of the polycrystalline alkali metal tetrafluorotetracyanoquinodimethan(TCNQF 4) charge transfer salts

Abstract

The entire series of alkali metal charge transfer salts of tetrafluorotetracyanoquinodimethan(TCNQF 4) have been synthesized and studied by electron spin resonance(ESR) techniques. The temperature dependence of the g-tensor, the temperature dependence of the relative magnetic susceptibility and the temperature dependence of the spectral envelope of each salt is discussed. The spectral properties of these salts are discussed in terms of the relationship between the size, electropositivity, and other physical properties of the alkali metal ion as one moves through the alkali metal series. The lithium salt exhibits a temperature independent g-tensor and the magnetic susceptibility follows Curie Law from 77 to 300 K. The ESR envelope of the sodium salt consists of two overlapping spectra. The magnetic susceptibility of both species is thermally activated. The spectral envelopes of the potassium and rubidium salts are similar in shape and behavior. Both are strongly dependent upon temperature. Their magnetic susceptibilities are thermally activated. The potassium salt has been studied from ca 4 to 300 K. An abrupt change in the spectral lineshapes of the potassium and rubidium salts is observed at ca 150 K. Finally, the spectral envelope of the cesium salt displays a unique monotonic decrease in linewidth with temperature.