The crystal and molecular structure of 2,2-dimethyl-4,4,6,6-tetrafluorocyclotriphosphazene

Crystals of the title compound are orthorhombic, a = 7.387(1), b = 8.502(2), c = 14.662(2) Å, Z = 4, space group Pnma. The structure was solved by direct methods and refined by least-squares procedures to a final R of 0.058, R w = 0.097 for the 530 reflections with I > 3σ(I). The P 3 N 3 ring is slightly but significantly non-planar with a crystallographically-imposed mirror plane normal to the ring, and the PN bond lengths in order from the PMe 2 group are 1.601(7), 1.552(7), and 1.560(6) Å. The ring angles are 114.0(4)°, (PMe 2 ); 120.0(4)°, PF 2 ; 123.2(5)°, N(3); 119.6(5)°, N(4). The mean exocyclic bond lengths are P—C, 1.77(1), P—F, 1.522(6), and the exoangles are 107.4(4)° (PMe 2 ) and 97.2(3)°, (PF 2 ). The bond lengths within the ring are well described in terms of simple perturbation theory, but comparison with the structures of other molecules shows the importance of factors other than π-electron distribution.