Molecular structures of non-geminally substituted phosphazenes. Part I. Crystal structure of 2,cis-4,trans-6,trans-8-tetrakismethylamino-2,4,6,8-tetraphenylcyclotetraphosphazene

Abstract

The crystal structure of the title compound has been determined from X-ray diffractometer intensity data and refined by least-squares methods to R 0·068 for 2913 reflexions. The crystals (γ-modification, m.p. 130·5°) are triclinic with a= 10·88 ± 0·03, b= 11·37 ± 0·03, c= 6·30 ± 0·02 Å; α= 95·7°, β= 100·2°, γ= 85·4°(all ±0·2°); Z= 1, space group P. The molecule occupies a crystallographic centre of symmetry and the phosphazene ring has the chair conformation, with approximate symmetry 2/m(C_2h). Mean bond lengths (Å) are : P–N(cyclic) 1·593, P–N(exocyclic) 1·672, and P–C 1·808. There are two different P–N–P angles in the ring: 124·6 and 131·3°. The molecule is very similar in shape to that of its parent compound N₄P₄Cl₄Ph₄.