Van-der-Waals based solvates of C60 with CBr2Cl2 and CBr2(CH3)2
Résumé
We demonstrate that solvates of fullerene C-60 form very predictable structures with finely tunable properties through the choice of the second component or solvent. Cubic co-crystals of C-60 center dot 12CCl(2)Br(2) and C-60 center dot 12CBr(2)(CH3)(2) were grown at room temperature in saturated solutions of fcc C-60 and the respective solvents (with C-2v molecular symmetry) They are unstable in air and transform spontaneously into the hexagonal co-crystals C-60 center dot 2CCl(2)Br(2) or C-60 center dot 2CBr(2)(CH3)(2). Whereas, the cubic co-crystals have positive excess volumes (+ 2% and + 5%, respectively), the stable hexagonal crystals, for which structures are given for the first time, possess negative excess volumes (-5% and -4.3%, respectively). The unit-cell volumes for both cubic and hexagonal co-crystals depend exclusively on the van-der-Waals volumes of the constituents and this correlation has been confirmed using previously published data.