An elusive phase transition inNa2RbC60

The ternary Na 2 RbC 60 fulleride is studied by variable-temperature solid-state 13 C and 23 Na NMR spectroscopies; in addition to the well known orientational order/disorder transition, a phase transformation to a low-symmetry phase which likely contains bonded C 60 3- moieties is identified at low temperature for the first time.