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

Paramagnetic vanadocene gives easily recordable 1H and 13C solid-state NMR signals which are shifted by more than 300 and 500 ppm (to high and low frequency, at room temperature), respectively. The strong temperature dependence of these shifts is the basis of new NMR signal shift thermometers for solutions and for the solid state. Since different signal shifts are found for the two states, primary referencing is established by using a resistance thermometer for solutions and absorbed glycol for the solid state. In the MAS experiment the sample temperature, Ts, depends linearly on the temperature set on the controller, as verified for five rotor spinning rates, νr, between 6 and 12 kHz. The slope and the intercept of the calibration curves depend on νr. In a Tsvs. νr2 plot, a non-linear correlation is found. In addition to 1H, 13C is a useful nucleus for measuring Ts. With simple spectrometer handling and favourable signal shift data, vanadocene meets the requirements of an internal temperature standard for MAS NMR studies. © 1997 John Wiley & Sons, Ltd.