VANADOCENE AS A TEMPERATURE STANDARD FOR C-13 AND H-1 MAS NMR AND FORSOLUTION-STATE NMR-SPECTROSCOPY

Paramagnetic vanadocene gives easily recordable H-1 and C-13 solid-sta te NMR signals which are shifted by more than 300 and 500 ppm (to high and low frequency, at room temperature), respectively. The strong tem perature dependence of these shifts is the basis of new NMR signal shi ft thermometers for solutions and for the solid state. Since different signal shifts are found for the two states, primary referencing is es tablished by using a resistance thermometer for solutions and absorbed glycol for the solid state. In the MAS experiment the sample temperat ure, T-g, depends linearly on the temperature set on the controller, a s verified for five rotor spinning rates, v(r), between 6 and 12 kHz. The slope and the intercept of the calibration curves depend on v(r). In a T-g vs. v(r)(2) plot, a non-linear correlation is found. In addit ion to H-1, C-13 is a useful nucleus for measuring T-g. With simple sp ectrometer handling and favourable signal shift data, vanadocene meets the requirements of an internal temperature standard for MAS NMR stud ies.