MOLECULAR-STRUCTURE OF THE FULLERIDE ANIONS IN SUPERCONDUCTING K3C60 AND INSULATING K6C60 DETERMINED BY POWDER NEUTRON-DIFFRACTION

The structures of K3C60 and K6C60 are refined by Rietveld analysis of high-resolution time-of-flight powder neutron diffraction data. Bond l ength and angle constraints are not necessary to produce chemically se nsible molecular structures for the fulleride anions. The results sugg est loss of the distinction between single and double bonds on the ful lerene molecule on reduction and are consistent with recent ab initio calculations. A simple chemical interpretation of the observed trends is given.