Solid-state studies of C60 solvates formed with chlorodibromomethane

At room temperature, the unstable-in-air hexagonal C-60 center dot 2HCClBr(2) solvate (a = 10.154(3)angstrom, c = 10.150(3) angstrom at 308 K) forms with a negative excess volume, and slowly transforms upon ageing at room temperature into a stable orthorhombic solvate, C-60 center dot 1.5HCClBr(2) (a = 23.009(5) angstrom, b = 12.649(6) angstrom, c = 11.659(5) angstrom). The lattice expansion and the lattice anisotropy of the C-60 center dot 2YCCl(3) (Y = H, CH3, Br, Cl) and C-60 center dot 2HCBr(3) solvates, for which the solvent molecular symmetry is C-3v are compared to the new results obtained for C60 solvates formed with HCClBr2 (solvent molecular symmetry C-2v). Results indicate that the van der Waals volume of the solvent molecule fully controls both the unit-cell volumes of the C60 intercalated halogenomethane solvates and the lattice expansion along the (001) hexagonal direction, the solvent molecular symmetry being an irrelevant physical parameter in the temperature range studied. (C) 2007 Elsevier B.V. All rights reserved.