THE STRUCTURE OF THE C60 MOLECULE - X-RAY CRYSTAL-STRUCTURE DETERMINATION OF A TWIN AT 110-K

Single-crystal x-ray diffraction methods were used to determine the crystal and molecular structure of C60 buckminsterfullerene. At 110 kelvin C60 is cubic, apparent Laue symmetry m3m, but it exhibits noncrystallographic systematic extinctions indicative of a twin in which I(hkl) and I(khl) are superimposed. In fact, C60 crystallizes with four molecules in space group T(h)6-Pa3BAR of the cubic system (Laue symmetry m3) with lattice constant a = 14.052(5) angstroms (angstroms) at 110 kelvin. The twin components are equal. A given component, which has crystallographically imposed symmetry 3BAR (C3i), displays an ordered structure of a truncated icosahedron. The five independent C = C bonds that join C6 rings average 1.355(9) angstrom; the ten independent C-C bonds that join C6 and C5 rings average 1.467(21) angstrom. The mean atom-to-atom diameter of the C60 molecule is 7.065(3) angstrom. The molecules are very tightly packed in the crystal structure, with intermolecular C...C distances as short as 3.131(7) angstrom.