X-ray diffraction studies show that the stable phase of the alkali fullerene RbC60
is orthorhombic (o-RbC60) below 350 K. C60 molecules form chains along a with an unusually
short spacing of 9.12 angstrom and magnetic properties suggest that o-RbC60 is a quasi-1
D metal with a transition to a spin density wave ground state at 50 K. The high temperature
fcc phase of RbC60 may be stabilized below 300 K by quenching from 500 K; it is paramagnetic
above 300 K and transforms into a nonmagnetic ground state between 300 and 250 K.
