Giant motion of La atom inside C82 cage

An anomalous charge density distribution of La atom encapsulated in a C82 cage has been revealed for La@C82 by the maximum entropy method (MEM)/Rietveld analysis using synchrotron powder diffraction data. The obtained La atom charge density shows a feature almost like a bowl or a hemisphere, suggesting that the La atom has a giant motion (large amplitude motion) inside the C82 cage at room temperature. From the obtained MEM charge density, the main results are (1) the cage structure of La@C82 (I) has C2V symmetry; (2) La atom locates at an off-centered position adjacent to a six-membered ring of the carbon cage; (3) the nearest La–C distance is 2.55(8) Å and (4) the amount of charge transfer from the La atom to the carbon cage is about 3.2 e, which corresponds to the nominal electronic structure, La3+@C823−.