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.