Anharmonic Thermal Motion and Low Temperature Phase Transition in Tetrathylammonium Octahydrido[triphenylphosphine]rhenate (1-).

The Re atom in [( C sub 2 H sub 5 ) sub 4 N] sup + [H sub 8 ReP(C sub 6 H sub 5 ) undergoes significant anharmonic thermal motion both at 295 and 163K, with resulting Re-H distances that are about 10% longer and Re-P distances about 6% longer than usual. The eight H and one P atom form a distorted equatorially- girdled trigonal prism about Re with the P atom occupying a prism corner. The low temperature phase contains two independent molecules in the asymmetric unit, with anionic displacements between 295 and 163K that do not exceed 0.25 angstroms but with cationic displacements as large as 1.8angstroms.