Kittle, Kevin Jeffrey (1987)
NMR relaxation and self diffusion studies of thallium compounds.
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205Ti NMR relaxation and self-diffusion measurements were applied to study the probe qualities of thallium cations in sucrose/solvent systems. The value of variable field/variable temperature relaxation measurements in defining relaxation behaviour was demonstrated. The relaxation of the dimethylthallium(III) cation in 60% sucrose/D20 (w/w) solution is dominated by the GSA mechanism at both high and low field. It was necessary to use a temperature dependent Fuoss-Kirkwood distribution of correlation times to rationalise the R1 data and this analysis gave the shielding anisotropy of the cation as 5588 +/- 173ppm, in keeping with previous studies. Similar behaviour was noted for the diethylthallium cation in sucrose/DMSO-d6 solutions (>10% concentration) and a concentration dependence in the distribution width parameter was observed. The 13C relaxation in aqueous sucrose solution at 60% concentration similarly showed complex behaviour. Self-diffusion and relaxation studies on thallium(I) ion in sucrose/D2O solutions showed the cation to be a good diffusional probe in viscous solutions, but a poor probe of reorientational motion. Studies on the self-diffusion of the dimethylthallium(III) cation in D20 were consistent with a solvent structure - limited model for translational motion. Further studies in sucrose/D20 solutions showed the dimethylthallium(III) cation to be limited to studying solutions 30% concentration. Studies of Ti(I)+ ion in aqueous TANOL solutions showed an inverse frequency dependence of R1 and R2 and a dominant electron-nuclear scalar relaxation mechanism was proposed. Finally, 205Ti and 203Ti R1 measurements in neat and diluted thallium(I) ethoxide showed that in the neat solution the rates for both nuclei were equal at high field and were dominated by the GSA mechanism. At low field, 203Ti R1 > 205Ti and a dominant scalar mechanism was proposed. In dilute solution the rates were equal at both high and low field and no GSA contribution was observed.
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Institution: University of London, Royal Holloway and Bedford New College (United Kingdom).