4,4'-Diiodobiphenyl (DIB) gave only one 127I NQR line corresponding to the ±1/2<-->3/2 transition. Zeeman effect of the 127I resonance line was studied at room temperature in a single crystal of DIB. Four nonequivalent electric field gradient (efg) systems were observed. It was deduced on the basis of the orientations of the efg axes that in the crystal the benzene rings in the molecule are mutually inclined at an angle of 77.8°±0.5°and the angle between the C-I bonds is 176.1°±0.1°.
Temperature dependence of the resonance frequency was interpreted in terms of torsional motions of the DIB molecules.