Ordered and disordered solvates of C60 and CBrCl2H

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, C-60 and CBrCl2H solvates have been studied. Hexagonal P6/mmm C-60 center dot 2CBrCl(2)H solvates transform at 373 K to monoclinic C2/c C-60 center dot CBrCl2H solvates. While orientational disorder typical for C-60 is found in the hexagonal solvates (as found in many C-60 halomethane solvates), in the monoclinic solvates, C-60 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 C-60 center dot halomethane solvates.