Molecular structures of non-geminally substituted phosphazenes. Part II. Crystal structure of 2,cis-4,cis-6,cis-8-tetrachloro-2,4,6,8-tetraphenylcyclotetraphosphazatetraene

Abstract

Crystals of the title compound (α-modification, m.p. 190 °C) are triclinic, a= 14·07, b= 11·67, c= 9·00 Å, α= 99·7, β= 88·5, γ= 102·1°, space group P, Z= 2. The structure was solved by direct methods; atomic positions were determined by least-squares refinement from X-ray diffractometer intensity data, the final R being 0·056 for 4519 reflections. The eight-membered phosphazene ring has an irregular crown conformation with P–N–P angles ranging from 133·1 to 142·0°. Mean bond lengths are: P–N 1·570, P-Cl 2·041, P–Cl 1·783, and C–C 1·39 Å. The bond lengths are discussed in terms of the electronegativity of the exocyclic groups and the ring conformation is discussed in terms of steric factors.