Crystal and molecular structure of 2,2,4,4,6,6-hexafluoro-8,8-dimethylcyclotetraphosphazene

Abstract

Crystals of 2,2,4,4,6,6-hexafluoro-8,8-dimethylcyclotetraphosphazene, N₄P₄F₆Me₂, are monoclinic, a= 9·355(5), b= 12·400(5), c= 11·132(5)Å, β= 113·75(3)°, Z= 4, space group I2/a. The structure was determined with diffractometer data by Patterson, Fourier, and full-matrix least-squares methods, the final R being 0·067 for 621 observed reflexions. The phosphazene ring is situated on a C₂ symmetry axis and has the ‘saddle’ conformation, but tends strongly towards planarity. The most interesting features of the ring are four distinct P–N bond lengths (1·584, 1·470, 1·532, and 1·487 Å), and large valency angles (145°) at nitrogen, which are explicable in terms of π-bonding theories.