IR and UV spectral and differential thermal analyses of symmetry shifts in geminally bis-, tetrakis- and fully substituted phenyl derivatives of cyclotriphosphazene

Abstract

The effect of geminal arylation on the hexachlorocyclotriphosphazatriene molecular structure and on the thermodynamics has been investigated by infrared and ultraviolet spectroscopy and by differential thermal analysis. The spectral and thermal evidence suggest that D 3h is the point group to which the molecular symmetry of this compound should be referred. Arylation to both the bisphenyl and tetrakisphenyl derivatives reduces the molecular symmetry to the C 2v point group, which influences the spectral and thermal features dramatically. Further arylation to the hexaphenyl derivative raises the symmetry to puckered C 3v, which undergoes a thermal shift into the higher D 3h point group. Except for the hexaphenyl derivative, all the studied phosphazenes show only a solid-liquid phase transition. The hexaphenyl derivative shows an additional solid-solid phase transition, which can probably be attributed to the proposed solid state C 3v- D 3h point-group symmetry transfer. Protonation of the phenyl phosphazenes is expected to proceed symmetrically at the three nitrogen atoms of the ring, because the molecular symmetry is maintained, as shown by the unshifted spectral features. However, the protonation process shifts the molecular structure into a more associative, rigid solid phase, which influences the spectral and thermal features and provides a broader, more diffused structure.