Gd-L-III EXAFS study of structural and dynamic properties of Gd@C-82 between 10 and 300 K

The location of endohedral Gd ions in Gd@C-82 is studied by Gd-L-111 X-ray absorption spectroscopy in the temperature range 10-300 K. The near-edge da ta point to a covalent bond of trivalent Gd ions with the carbon cage. The EXAFS data can be well fitted with a Gd position above a carbon hexagon wit h two neighbour shells of carbon at distances R-1.2=2.49(3) and 2.95(5) Ang strom, corresponding to a large off-center position of about 1.8 Angstrom f rom the center of the C-82 cage. The second cumulants of these distances ar e relatively large and weakly depending on temperature. This points to a co nsiderable distribution in Gd-C-1 and Gd-C-2 distances and confirms the rel atively strong binding of the Gd ion to the C-82 cage. These results will b e discussed together with previous EXAFS studies and theoretical calculatio ns of Y@C-82 and La@C-82. (C) 1999 Elsevier Science Ltd. All rights reserve d.