Structure and Molecular Motions in Rubidium Tetraphenylborate

Abstract

By X-ray diffraction it was found that at 293 K the crystals of rubidium tetraphenylborate are tetragonal, space group I42m, a = b = 11.212(2) Å, c = 8.098(2) Å , with 2 molecules of Rb+[C24H20B]- in the unit cell. The molecular reorientations as functions of temperature were studied by 1H NMR. Two types of motions were detected: an anisotropic reorientation of the tetraphenylborate anions about their mass centres, and small-angle reorientations / oscillations of the phenyl rings. The dependence of the potential energy of the anion in the crystal on the angle of the phenyl ring rotation about the B-Ph bond was obtained on the basis of atom-atom calculations. The dynamics of this compound was compared to that of tetraphenyltin.