Crystal and molecular structure of octamethoxycyclotetraphosphazene

Abstract

Crystals of octamethoxycyclotetraphosphazene, N₄P₄(OMe)₈, are orthorhombic, a= 17·85, b= 16·55, c= 13·06 Å, space group Pbca with Z= 8. The atomic positions have been determined by least-squares refinement from X-ray diffraction data, the final R being 0·078 for 1305 reflexions. The eight-membered phosphazene ring has a slightly distorted saddle shape with a mean P–N bond length of 1·57 Å and mean angles N–P–N 121 and P–N–P 132°. The phosphorus atoms are almost coplanar but the nitrogen atoms are alternately 0·5 Å above or below their plane. The mean length of the P–O bond, 1·58 Å, and the mean P–O–C angle, 121°, suggest π-bonding between phosphorus and oxygen atoms although steric repulsions appear to be the main factor governing the orientation of the methoxy-groups.