DYNAMICS OF THE BENZENE MOIETY IN CRYSTALLINE BENZENETRICARBONYLCHROMIUM - POTENTIAL AND LIMITATIONS OF H-2 NMR LINE-SHAPE ANALYSIS AND H-2 NMR SPIN-LATTICE RELAXATION-TIME MEASUREMENTS

The dynamic properties of the benzene moiety in perdeuterated benzenetricarbonylchromium (eta(6)-C6D6)Cr(CO)(3) have been investigated via analysis of H-2 NMR line shapes and measurement of H-2 NMR spin-lattice relaxation times. The temperature dependence of the quadrupole echo H-2 NMR lineshape and the temperature dependence of the H-2 NMR spin-lattice relaxation time are interpreted in terms of a 2 pi/6 nearest-neighbor jump model of the benzene moiety about an axis perpendicular to the molecular plane. The activation energy for this motion is estimated to be 17.7 kJ mol(-1) (from H-2 NMR spin-lattice relaxation time measurements). The potential and limitations of H-2 MMR line-shape analysis and H-2 NMR spin-lattice relaxation time measurements for distinguishing different dynamic models for in-plane rotation of benzene and other molecular reorientational processes are discussed.