Pentacoordinated Molecules. VI. The Electric-Dipole Moment of PCl3F2 and PCl2F3 in the Gaseous State

From a study of the temperature variation of the dielectric constant over the range from −30° to +19°, a value of 0.68±0.02 D was obtained for the vapor-state electric-dipole moment of PCl2F3 and 23.4±0.5 cc for the induced polarization. A similar study on PCl3F2 showed no detectable change in the molar polarization over the temperature interval extending from −13° to +30°. A zero dipole moment is assigned in agreement with previous structural information on this molecule. The induced polarization is 32.0±0.2 cc. The reliability of the measurements were determined by studying gaseous ammonia and dimethyl ether over the same temperature region. The high dipole moment of PCl2F3 compared to the gas-state value observed for PCl4F (0.21 D) is attributed primarily to differences in bonding between equatorial and axial positions of a trigonal biypramid with distortion acting as a secondary factor.