We demonstrate that solvates of fullerene C60 form very predictable structures with finely tunable properties through the choice of the second component or solvent. Cubic co-crystals of C60·12CCl2Br2 and C60·12CBr2(CH3)2 were grown at room temperature in saturated solutions of fcc C60 and the respective solvents (with C2v molecular symmetry) They are unstable in air and transform spontaneously into the hexagonal co-crystals C60·2CCl2Br2 or C60·2CBr2(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.

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