Ordered and disordered solvates of C60 and CBrCl2H

Abstract

The formation of co-crystals is often unexpected; however, the Buckminster fullerene, for which many solvates are known, is an excellent system to study this tendency. In the present paper, C₆₀ and CBrCl₂H solvates have been studied. Hexagonal P6/mmm C₆₀·2CBrCl₂H solvates transform at 373 K to monoclinic C2/c C₆₀·CBrCl₂H solvates. While orientational disorder typical for C₆₀ is found in the hexagonal solvates (as found in many C₆₀ halomethane solvates), in the monoclinic solvates, C₆₀ appears to be orientationally ordered. As for the solvent CBrCl₂H, two types of occupational disorder involving the distribution of the halogen atoms can be observed, comparable to the behaviour in the two polymorphs of pure CBrCl₂H. Within the monoclinic solvate, two sites are equally occupied by Br and Cl atoms (1/2 : 1/2), while one site is fully occupied by a Cl atom which leads to an average C_s symmetry for the solvent molecule. Whereas within the hexagonal solvates, each halogen position is occupied by 1/3 : 2/3 of Br or Cl atoms, respectively, leading to an average C_3v molecular symmetry. The anisotropy of the intermolecular interactions coincides with the symmetry of the solvate structures and can be generalized for the C₆₀·halomethane solvates.