Evidence for Distinct Polymer Chain Orientations inKC60andRbC60

The ${\mathrm{KC}}_{60}$ and ${\mathrm{RbC}}_{60}$ 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 ${\mathrm{KC}}_{60}$ and ${\mathrm{RbC}}_{60}$ possess different chain orientations about their axes, which are described by distinct space groups $\mathrm{Pmnn}$ and $I2/m$, respectively. Such a structural difference will be of great importance to a complete understanding of the physical properties.