Crystal and molecular structure of hexadeca (dimethylamino) cyclooctaphosphazene

Abstract

Crystals of the title compound are monoclinic, a= 17.383(5), b= 24.167(7), c= 14.637(6)Å, β= 111.16(2)°, space group C2/c. The structure was determined by direct methods from diffractometer X-ray data and refined by full-matrix least-squares methods to R 0.038 for 1 920 observed reflexions. The molecule occupies a crystallographic centre of symmetry. Mean endo- and exo-cycli P–N bond lengths are 1.548(9) and 1.651(7)Å P–N–P angles range from 145.9(4) to 170.2(5)°, mean 156.5°, and endocyclic N–P–N angles range from 114.8(3) to 119.2(3)°, mean 116.8° Three exocyclic N–P–N angles are nearly equal, mean 101.5(7)°, the fourth being significantly larger, 106.1(3)°. Mean N–C is 1.43(2)Å, and mean C–N–C angle 113.9(8)°. The molecular confirmation is very similar to that of [NP(OMe)₂]₈; structural comparisons are also made with the dimethylamides [NP(NMe₂)₂]_3,4,6.