We have used {sub 45}Sc solution NMR spectroscopy to show for the first time the internal motion of the scandium ions in two Sc{sub 2}C{sub 84} isomers. In one isomer the two scandium ions are equivalent over the temperature range 238-433 K, whereas in the second isomer there are two inequivalent scandium ions below 383 K. At 383 K coalescence occurs, and above that temperature the scandium ions become equivalent. The processes are reversible, and we believe this is the first time such phenomena have been observed. 27 refs., 4 figs.