Knowledge Bank

The vibrational spectrum of the thermally unstable $CF3PCl4$ molecule was observed in the Raman effect $(\Delta \nu =50-1500cm-1)$ and in infrared absorption $(280-2000cm-1)$. The data agree with that expected for a molecule having a trigonal bipyramidal structure in which the $CF3$ group assumes an axial position. Although all of the active fundamentals are assigned, the existence of an appreciable torsional barrier to internal rotation of the $CF3$ group is not confirmed. The phosphorus atom, however, is apparently coplanar with the three equatorial chlorine atoms. Other structures involving an equatorial $CF3$ group in a trigonal bipyramid or an axial $CF3$ group in a tetragonal pyramind are considered and rejected.