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 RbC6 0 are presented. While powder diffraction studies showed no definite struct ural differences, the single crystal diffraction data analysis reveals diff erent relative chain orientations in the two compounds. They are discussed in relation with semi-empirical energy calculations. The structural differe nce between KC60 and RbC60 may be a key feature for the understanding of th eir contrasted conducting and magnetic properties.