Evidence for distinct polymer chain orientations in KC60 and RbC60
  The KC60 and RbC60 polymer phases exhibit contrasting electronic properties while powder diffraction studies have revealed no definite structural difference. We have performed single crystal X-ray diffraction and diffuse scattering studies of these compounds. It is found that KC60 and RbC60 possess different chain orientations about their axes, which are described by distinct space groups Pmnn and I2/m, respectively. Such a structural difference will be of great importance to a complete understanding of the physical properties. 
P. Launois, R. Moret, J. Hone, A. Zettl