Intramolecular Hindrances to CCl3 Reorientations in CCl3PCl4 and (CCl3)2PCl3 Crystals

The trigonal bipyramidal structure of trichloromethyl-tetrachlorophosphorane CCl₃PCl₄ and bis(trichloromethyl)trichlorophosphorane (CCl₃)₂PCl₃ molecules with apical CCl₃ groups is responsible for steric hindrances to reorientations of these groups around the C–P bond. The intramolecular barriers to CCl₃ reorientations calculated for the two phosphoranes (Hartree–Fock method using the 6-31G(d) basis set) are 105.9 kJ/mole and 106.6 kJ/mole, respectively. These internal barriers are high enough to block the reorientational motion of the CCl₃ groups, as found previously by ³⁵Cl NQR for the stated crystals.