Conformational studies of the phosphazenyl side chain in cyclophosphazenes. Part 3. Crystal and molecular structure of N3P3Cl4(NEt2)(NPPh3)

Abstract

The crystal structure of N₃P₃Cl₄(NEt₂)(NPPh₃) has been determined. The crystals are orthorhombic, space group Pbca, with a= 8.208(1), b= 21.890(1), c= 31.722(2)Å, Z= 8, and m.p. = 146.5 °C. The structure was solved by direct methods and refined to a final R value of 0.045 for 2 025 independent reflections. The analysis reveals significant variations in the ring P–N bond lengths. The two nitrogenous substituents, NPPh₃ and NEt₂, reside on the same phosphorus atom. The latter, NEt₂, has an almost exact type II conformation (the plane NC₂ almost perpendicular to the local NPN plane)(the first observed for a dialkylamino-group in cyclophosphazenes), the former, NPPh₃, deviates from type II towards type III (in type III the plane P_ring–N–P_exo makes an angle of ca. 45° with the local N–P–N ring plane). The present structure is compared with others of triphenylphosphazenyl-cyclophosphazenes and the conformation of the NPPh₃ substituent and its electron supply in the ground and perturbed states are discussed.