Proton Relaxation Times and Bromine Nuclear Quadrupole Resonance Frequencies in Brominendash;Benzene 1:1 Complex

摘要

Proton relaxation times (T1) were measured inBr2middot;C6H6complex from the melting point (259deg;K) to 130deg;K.T1data exhibit a minimum which corresponds to the reorientation of the benzene ring about the sixfold axis. The mean activation energy for this process is5.0 plusmn; 0.3thinsp;kcal moleminus;1and the correlation time for the motion is8 times; 10minus;11secjust below the melting point. The brominehyphen;81 nuclear quadrupole resonance (NQR) frequency extrapolated to 0deg;K is 319.75 MHz. The81Br signal is very weak and asymmetric, but appears to correspond to theBr2middot;C6H6complex. Evidence for a phase transition near 60deg;K is presented. As pointed out earlier by Hooper, the proximity of the bromine NQR frequency in the complex to that for the Br2molecule in solid Br2demonstrates that the complex is not a ``chargehyphen;transfer'' complex in the usual sense but rather is bound by van der Waals and classical electrostatic forces.