The cation and anion Of Y@C-82 were prepared by controlled potential electrolysis, and their stabilities were investigated by spectroscopic methods. The anion is found to be much more stable than the cation under an air atmosphere. The cage structure of Y@C-82 was determined by observing the C-13 NMR spectrum of the stable diamagnetic anion. It is confirmed that Y@C-82 has C-2v symmetry. (c) 2005 Elsevier B.V. All rights reserved.