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

Three new polymorphs of C60·2S8 were discovered. The previously known structure (first reported by Roth and Adelmann in 1993 hereby designated as α) crystallizes in space group C2/c with Z = 4 and changes to a triclinic structure (β) in space group P1̅ 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 (γ) crystallizes in space group P21/c with Z = 4 at room temperature and undergoes a phase change to Pc (δ) 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 C60 molecules. Both of the phase changes are reversible.