Low temperature H-1-, F-19-, and P-31-PGSE diffusion measurements. Applications to cationic alcohol complexes

The problems associated with low-temperature pulsed-gradient spin-echo (PGSE) NMR diffusion measurements are discussed. The influence of convection is overcome by employing a coaxial insert inside a normal 5 mm NMR tube. By means of this configuration, correct diffusion constants and temperature-independent hydrodynamic radii can be obtained. Low-temperature H-1-, F-19-, and P-31-PGSE measurements on unstable cationic alcohol complexes of palladium and tungsten (in MeOH and CH2Cl2) are reported. For [W(Cp)(adamant-1-ol)(CO)(3)](CF3SO3), a strong hydrogen bond between the alcohol OH group and the trifluoromethanesuffonate anion is demonstrated.