Crystal and molecular structure of hexaphenoxycyclotriphosphazene, [NP(OPh)₂]₃

Crystals of hexaphenoxycyclotriphosphazene, [NP(OPh)₂]₃, are monoclinic, a= 11·176(4), b= 19·270(3), c= 16·171 (4)Å, β= 92·07(2)°, Z= 4, space group P2₁/n. The structure was determined with diffractometer data by Patterson and electron-density methods, and refined by block-diagonal least-squares methods to R 0·037 for 2899 observed reflexions. The cyclotriphosphazene ring is slightly non-planar, with two nitrogen atoms displaced by 0·15 Å in opposite directions from the plane of the other four (three phosphorus and one nitrogen) atoms. The conformations of the phenoxy-groups are different at the three phosphorus atoms, and there are small deviations among chemically equivalent angles; these differences are probably a result of intra- and inter-molecular steric effects. There are no differences among chemically equivalent bond lengths, the mean distances being P–N 1·575(2), P–O 1·582(2), and O–C 1·406(3)Å.