The Bromine Nuclear Quadrupole Resonance of the Molecular Complex of Aluminum Tribromide with Benzene

The bromine nuclear quadrupole resonance (NQR) and its Zeeman effect have been observed in the molecular complex of aluminum tribromide with benzene at room temperature. The resonance frequencies are 79.99, 90.10, and 91.18 MHz for 81Br at 301°K. The asymmetry parameters of the field gradient are 28.9±1.1, 8.6±1.0, and 6.0±0.9% for the bromine atoms in the order of increasing resonance frequency. Aluminum tribromide forms the dimer in the complex crystal as well as in the pure state. The bond angle between a pair of terminal bromine atoms and the interbond angle at the bridging bromine atom are found to be 117.3±0.5° and 95.5±0.2° respectively; these values correspond to those of 122±2° and 87±2° obtained from the X-ray analysis. Furthermore, the charge-transfer from the benzene ring to the bromine atom is discussed on the basis of the NQR parameters.