A Series of Polymorphs of Hexakis(4-fluorophenoxy)cyclotriphosphazene

A series of conformational polymorphs of hexakis­(4-fluorophenoxy)­cyclotriphosphazene have been identified and characterized. Three of the four polymorphs are previously unreported. Thermal analysis coupled with variable temperature powder X-ray diffraction has shown that conversion between polymorphs occurs at well-defined temperatures. The high temperature form is metastable at room temperature and is never obtained from solution. Two forms are observed in solution crystallization experiments, a monoclinic form and a triclinic form. Slurry experiments revealed that the triclinic form is the most stable at room temperature. The fourth polymorph is observed only at low temperatures. Interconversion between three of the polymorphs occurs in a single-crystal to single-crystal manner.