First single-crystal X-ray structural refinement of the rhombohedral C60 polymer

The single crystals of the rhombohedral C-60 polymer were prepared by the polymerization of C-60 single crystals under a high pressure of 5 GPa at 773 K. The X-ray structure analysis revealed that it crystallized in a rhombohedral space group R (3) over barm, Z = 3 with a = 9.175(l) c = 24.568(3). The refinement of 49 parameters with 442 data converged to R1 = 0.0679 (for I > 2sigma(I)) and wR2 = 0.1586 (all data). The crystal structure is composed of hexagonal 2D layers formed by the polymerization of C-60 molecules via [2+2] cycloaddition. Three of those layers are stacked rhombohedrally in the unit cell along the c-axis and held together by C...C van der Waals forces. The present structural model differs from a well-known proposed one, in which each C-60 unit rotates 60degrees about the crystallographic 3-fold axis. This is the first single-crystal X-ray structural refinement of polymerized C-60. (C) 2002 Published by Elsevier Science B.V.