New Insights into the Structural Complexity of C60•2S8: Two Crystal Morphologies, Two Phase Changes, Four Polymorphs

Three new polymorphs of C-60 center dot 2S(8) were discovered. The previously known structure (first reported by Roth and Adelmann in 1993 hereby designated as a) crystallizes in space group C2/c with Z = 4 and changes to a triclinic structure (beta) in space group P (1) over bar with Z = 4 when the temperature is decreased below 260 K. The room-temperature structure was reinvestigated, and the new, ordered, low-temperature structure is described. A new, concomitant, polymorph (gamma) crystallizes in space group P2(1)/c with Z = 4 at room temperature and undergoes a phase change to Pc (delta) with Z = 4 when the temperature is decreased below 180 K. As indicated by geometric and temperature factor changes, it is clear that the low-temperature phases represent an increase in the level of order in the arrangement of C-60 molecules. Both of the phase changes are reversible.