Three new polymorphs of C 60 •2S 8 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, lowtemperature structure is described. A new, concomitant, polymorph (γ) crystallizes in space group P2 1 /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 C 60 molecules. Both of the phase changes are reversible.

Two related nickel­(II) porphyrins, etioporphyrin-I (Etio-I) and octaethylporphyrin (OEP), were cocrystallized with C70 to produce the new cocrystal structures C70·Ni­(Etio-I)­·2C6H6 and C70·Ni­(OEP)­·2C6H6. Etio-I is a variant of OEP, where four alternating ethyl groups from OEP are replaced with methyl substituents. This isomer of etioporphyrin has the potential to act as an agent in chiral sorting of asymmetric fullerenes. However, the replacement of four ethyl groups has nontrivial structural consequences. Further host–guest investigation of M­(Etio-I) (M = Co, Ni, Cu, Zn) with C60 or C70 was conducted, producing new X-ray structures of Co­(Etio-I) and Zn­(Etio-I), and a redetermination of Ni­(Etio-I). Despite numerous and varied attempts, C60 cocrystallized with M­(Etio-I) could not be obtained.

The single crystal X-ray structures of three well-ordered cocrystals of C 70 with brominated benzenes are examined. The crystals are those of C 70 • C 6 Br 6 •C 7 H 8 , C 70 •C 6 Br 6 •C 6 H 6 , and C 70 •2(1,2,4,5-tetrabromobenzene)•CS 2 . While all three structures exhibit extensive van der Waals interactions, the presence of a wavelike C−Br---Br structural motif is a distinctive part of the cocrystal assembly.In these three crystal structures, it is observed that the Br---Br interactions are a cross between type I and II halogen−halogen bonds. In our hands, this structural motif does not occur in structures with C 60 .

Fullerenes are fascinating to study in the solid state in regard to their supramolecular and host-guest chemistry. Through the utilization of single-crystal X-ray diffraction, the molecular and supramolecular structures of fullerenes can be determined. Much focus has been given to the host-guest nature of fullerenes in which the complementary molecules are often quite large and resemble the shape of the cage. Little focus, however, has been given to flat, smaller co-crystallization molecules. The molecules 1,2,4,5-tetrabromobenzene and hexabromobenzene were successfully co-crystallized with C60, C70 and Sc3N@Ih (7)-C80 in order to study π-π interactions. While the C60 structures show typical van der Waals interactions, the higher fullerenes show additional, unique halogen-halogen interactions. Figure 1