The X‐Ray Crystal Structure and Packing of a Hexakis‐adduct of C60: Temperature dependence of weak CH…︁O interactions

Abstract

AbstractThe crystal structure and packing of the C60 hexakis‐adduct 1 has been determined from accurate X‐ray diffraction measurements. The largest deformations on the C60 surface occur within the bridged pyracylene subunits; the bridgehead 6–6 bond lengths of the four cyclopropane and the two cyclohexene rings, attached in pseudo‐octahedral positions, are close to 1.6 Å. Significant deformations also occur in the remaining part of the C60 skeleton, not bridged to any of the functional groups. The crystal packing, analyzed at 270, 230, and 180 K is characterized by a three‐dimensional network of 14 weak CH…︁O interactions. For most of these, H…︁O and C…︁O distances decrease on cooling the crystal specimen, indicating that they are attractive in nature. On the other hand, the shortest, nearly linear C(sp3)H…︁O contact seems to be repulsive, since cooling of the crystal specimen leads to significantly longer H…︁O and C…︁O distances and to a reduction of the CH…︁O linearity. Probably as a result of this intermolecular expansion, strain is produced in the crystal. Depending on the crystal‐mounting procedure, this can lead either to a disordered structure (below ca. 200 K), or to destruction of the crystal specimen.