Temperature dependent metal cluster position inside a C-82 cage: Sc-3@C-82

ESR studies on Sc-3@C-82 in dependence on the temperature and of the used s olvent have led to a new behaviour of the scandium cluster stabilization in side the carbon cages. A 22 line spectrum, which can be measured down to 20 0 K, is well known from the literature. In the region from 300 K to 200 K t he coupling constant of the scandium splitting increases reversibly with de creasing temperature. At 240 K a superposition of the 22 line spectrum and a single line appears. In the temperature range of 180 K and 150 K the obse rved single line forms the main part of the ESR spectrum. This effect is co mpletely reversible. This behaviour at low temperatures is explained by a model including the ch ance of the metal cluster position inside the C-82 cage below 200 K and the chemical pressure of the frozen solvent.