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Letters to Nature
Nature 353, 147 - 149 (12 September 1991); doi:10.1038/353147a0

Crystal structure and bonding of ordered C60

William I. F. David, Richard M. Ibberson, Judy C. Matthewman, Kosmas Prassides*, T. John S. Dennis*, Jonathan P. Hare*, Harold W. Kroto*, Roger Taylor* & David R. M. Walton*

ISIS Science Division, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire 0X11 OQX, UK
*School of Chemistry and Molecular Sciences, University of Sussex, Brighton BN1 9QJ, UK

STRUCTURAL studies1–.3 of crystalline C60 (ref. 4) have indicated that at room temperature the C60 molecules are orientationally disordered and the crystal structure may be regarded as a face-centred cubic configuration of C60 spheres. Below 249 K, however, the molecules become orientationally ordered3 and a simple cubic lattice results, corresponding to a symmetry change from Fm3¯ to Pa3¯. Here we present the results of a neutron powder diffraction study of the low-temperature ordered structure, which reveals the packing configuration of the C60 molecules. The C60 units are rotated in an anticlockwise manner around the [111] direction by ~98° from the ideal Fm3¯ configuration. This apparently arbitrary rotation in fact results from an optimized ordering scheme in which electron-rich short (1.391-Å) inter-pentagon bonds face the electron-poor pentagon centres of adjacent C60 units. The high symmetry of the C60 molecule allows these interactions to be optimized identically for all twelve nearest neighbours, a possibility that is by no means intuitively obvious. The bonds common to a given pentagon are somewhat longer (1.455 Å). The high degree of bonding optimization and the absence of bonding frustration accounts for the high ordering temperature of 249 K (ref. 5).

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References

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