Interrelation Between Molecular Motions and Structure in Solid Trimethylamine-boron-trichloride as Studied by NMR

The charge transfer complex trimethylamine-borontrichloride (TMABTC1), consisting of the electron donor trimethylamine and boron-trichloride, is a stable crystalline solid. Its molecular and crystal structure has been determined by Hess [1]. The crystals are monoclinic, space group P21/m, with a = 6.492, £» = 10.216, c = 6.649 Ä, 0=116.0° and two molecules per unit cell. The bond lengths and the angle found indicate that the complex may not have the ideal C3v symmetry. Since there is a close relation between the spatial arrangement of bounded atoms and the hindrance potential of motion of molecular subunits, these crystallographic differences should influence the motions in this complex; namely the rotation of the methyl groups about their three-fold symmetry axes (C3 motion) and the axial rotation of the trimethylamine moiety about the N B axis (C3 motion). To elucidate the relation between the structure and dynamic behaviour of the complex we have used NMR [2, 3].