Molecular structures of non-geminally substituted phosphazenes. Part IV. Crystal structure of 2,4,4,trans-6,8,8-hexachloro-2,6-bis(dimethyl-amino)cyclotetraphosphazatetraene

Abstract

Crystals of the title compound (Ib) are triclinic, a= 8·55, b= 8·68, c= 7·51 Å(all ±0·02Å), α= 105·3, β= 102·0, γ= 114·8°(all ±0·3°), space group P, Z= 1. The structure was determined from diffractometer X-ray intensity data by the heavy-atom method and refined by full-matrix least squares to R 0·053 for 2801 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. 1·580 and 1·558 Å. The P–Cl bonds in the non-geminal groups are considerably longer (2·062 Å) than those in the geminal groups (2·009 Å). The exocyclic P–N bond length is 1·618 Å. P–N–P angles in the ring are 130·9 and 137·6°. The dimethylamino-groups occupy equatorial positions, in which their intramolecular contact with the chlorine atoms is minimised.