Polymer chain orientations in KC60 and RbC60: structural analysis and relation with electronic properties

First single crystal X-ray diffraction studies of polymerized KC60 and RbC60 are presented. While powder diffraction studies showed no definite structural differences, the single crystal diffraction data analysis reveals different relative chain orientations in the two compounds. They are discussed in relation with semi-empirical energy calculations. The structural difference between KC60 and RbC60 may be a key feature for the understanding of their contrasted conducting and magnetic properties.