MOLECULAR-DYNAMICS IN THE SOLID TRIMETHYLAMINE-BORANE COMPLEX - A DEUTERIUM NMR-STUDY

The molecular dynamics of solid (CH3)(3)NBH3 is investigated by deuter ium NMR spectroscopy. Variable temperature lineshape analyses yield ac tivation energies of 27 +/- 3, 19 +/- 2, and 12.5 +/- 2 kJ/mol for -CH 3,-N(CH3)(3) and -BH3 rotation, respectively. Analysis of the temperat ure dependence of the spin-lattice relaxation times, T-1, gives activa tion energies of 33 +/- 3, 15 +/- 1.5, and 14 +/- 1.5 kJ/mol, respecti vely. Direct comparison of rotational exchange rates (from lineshape s imulations) an of rotational correlation times (from T-1 analyses) for -N(CH3)(3) and -BH3 rotation indicate that the two motions are correl ated in solid (CH3)(3)NBH3 and together constitute a whole molecule re orientation about the N-B bond. This is supported by an internal rotat ional barrier of 18.0 kJ/mol for -BH3 rotation, obtained from ab initi o molecular orbital calculations at the MP2/6-31G level.