An improved determination of the crystal structure of hexachlorocyclotriphosphazene (phosphonitrilic chloride)

Abstract

By use of X-ray diffractometer intensity data, the crystal structure of hexachlorocyclotriphosphazene, N₃P₃Cl₆, has been refined to R 0·048 for 1222 reflexions. The phosphazene ring is almost planar but there are small deviations from planarity of up to 0·04 Å. The P–N bonds are all equal in length, 1·581 Å(σ 0·004–0·005 Å) and the P–Cl bond lengths range from 1·991–1·995 Å(σ 0·004–0·005 Å). The mean N–P–N angle in the ring (118·4°) is significantly smaller than the mean P–N–P angle (121·4°). There are only slight deviations from the ideal molecular symmetry D_3h(m2). An analysis of the atomic thermal vibrations shows that at 25°± 2 °C the molecule is undergoing translational vibrations with root-mean-square amplitudes of 0·17–0·19 Å combined with angular oscillations about the molecular axes whose root-mean-square amplitudes are 3·4–3·6°.