Single C-C bond in (${\mathrm{C}}_{60}$${)}_2^{2\mathrm{-}}$

The structure of the dimer phases of ${\mathrm{RbC}}_{60}$ and ${\mathrm{KC}}_{60}$ were investigated by x-ray powder diffraction. We have established that the dimer molecule forms through a single C-C interfullerene bond in contrast to the four-membered rings of ${\mathrm{C}}_{60}$ polymers. Molecular orientation and space group symmetry were also determined. © 1996 The American Physical Society.