Molecular structures of non-geminally substituted phosphazenes. Part III. Crystal structure of 2,cis-4,trans-6,trans-8-tetrachloro-2,4,6,8-tetrakis(dimethylamino)cyclotetraphosphazatetraene

Abstract

Crystals of the title compound are triclinic, a= 12·67, b= 10·96, c= 8·68 Å, α= 92·6, β= 106·0, γ= 106·6°, space group P, Z= 2. The structure was determined from diffractometer X-ray data by Patterson and Fourier methods and refined by full-matrix least squares to R 0·098 for 2666 reflections. The eight-membered phosphazene ring has a hybrid crown-saddle conformation with P–N–P angles in the range 133·3–140·6°. Mean bond lengths are: P–N(endocyclic) 1·556, P–N(exocyclic) 1·626, P–Cl 2·043, and N–C 1·47 Å. Bond lengths are discussed in terms of the electronegativities of the exocyclic groups and the ring conformation compared with that in other phosphazene and cyclo-octane derivatives.