A comparison of 3-D Cu-DCNQI with 1-D Tl-DCNQI by ESR and NMR

Abstract

Among the large variety of highly conductive DCNQI-salts with metallic counterions, only (Me,Me-DCNQI)2Cu and (Me,Me-DCNQI)2Tl exhibit NMR behavior like the metals Cu and Tl, respectively, i.e. considerable Knight shifts and longitudinal relaxation rates of Cu and Tl nuclei. These seem point to a bonding between the DCNQIs and the counterions in both systems. Whereas in the copper salts there is no frequency dependence of the proton spin-relaxation rate. The T1H−1 of Tl-DCNQI is proportional to ω−12 pointing to a preferential 1-d electron spin-motion. In contrast to the copper salt, which exhibits NCN-Cu-NCN bridges, there is no charge- / spin carrier transportation by the counterion in the Tl-salt. This is deduced by narrow ESR lines and a conductivity, lower by an order of magnitude. The Knight shift is due to a core polarization of the 6s orbital at the Tl nuclei.