Molecular structures of non-geminally substituted phosphazenes. Part V. Crystal structure of 2,trans-6-dichloro-2,4,4,6,8,8-hexakis(dimethylamino)cyclotetraphosphazatetraene

Abstract

Crystals of the title compound are triclinic, a= 9·93, b= 9·39, c= 8·78 (all ±0·02)Å, α= 114·2, β= 114·7, γ= 93·4 (all ±0·3)°, space group P, Z= 1. The structure was determined from diffractometer X-ray intensity data and refined by full-matrix least squares to R 0·062 for 2359 reflexions. The molecule occupies a crystallographic centre of symmetry and the eight-membered phosphazene ring has the chair conformation with approximate symmetry C_2h(2/m). There are two significantly different P–N bond lengths in the ring, 1·586 and 1·555 Å. The P–Cl bonds (2·100 Å) are considerably longer than those in N₄P₄Cl₈. Exocyclic P–N bond lengths range from 1·640 to 1·669 Å. P–N–P angles in the ring are 135·3 and 135·5°. The non-geminal dimethylamino-groups occupy equatorial positions, where they avoid close contact with the other dimethylamino-groups in the molecule.