Crystal structures of three hexakis(fluoroaryloxy)cyclotriphosphazenes

Abstract

The syntheses and crystal structures of three cyclotriphosphazenes, all with fluorinated aryloxy side groups that generate different steric characteristics, viz. hexakis(pentafluorophenoxy)cyclotriphosphazene, N3P3(OC6F5)6, 1, hexakis[4-(trifluoromethyl)phenoxy]cyclotriphosphazene, N3P3[OC6H4(CF3)]6, 2 and hexakis[3,5-bis(trifluoromethyl)phenoxy]cyclotriphosphazene, N3P3[OC6H3(CF3)2]6 3, are reported. Specifically, each phosphorus atom bears either two pentafluorophenoxy, 4-trifluoromethylphenoxy, or 3,5-trifluoromethylphenoxy groups. The central six-membered phosphazene rings display envelope pucker conformations in each case, albeit to varying degrees. The maximum displacement of the `flap atom' from the plane through the other ring atoms [0.308 (5) Å] is seen in 1, in a molecule that is devoid of hydrogen atoms and which exhibits a `wind-swept' look with all the aromatic rings displaced in the same direction. In 3 an intramolecular C—H(aromatic)...F interaction is observed. All the –CF3 groups in 2 and 3 exhibit positional disorder over two rotated orientations in close to statistical ratios. The extended structures of 2 and 3 are consolidated by C—H...F interactions of two kinds: (a) linear chains, and (b) cyclic between molecules related by inversion centers. In both 1 and 3, one of the six substituted phenyl rings has a parallel-displaced aromatic π–π stacking interaction with its respective symmetry mate with slippage values of 2.2 Å in 1 and 1.0 Å in 3. None of the structures reported here have solvent voids that could lead to clathrate formation.

Polyphosphazenes: Phosphorus in Inorganic–Organic Polymers

“…Small-molecule derivatives serve a second purpose because many small-molecule phosphazenes are crystalline solids suitable for X-ray crystallography studies. 23 The resultant structural data can often be transposed to the polymers to suggest the magnitude of intramolecular interactions and other physical properties.…”