Cs4C60:: single phase synthesis and orientational order

Cs4C60 is reported as a pure phase for the first time, using low-temperature synthesis. It adopts an orthorhombic distortion of the body-centred tetragonal (bct) A(4)C(60) structure found for K4C60 and Rb4C60, due to the orientational ordering of the C-60(4-) anions with the 6:6 bonds directed along the orthorhombic b-axis. The caesium cations occupy two distinct distorted tetrahedral sites, producing the orientational order to avoid close contact with the five-membered rings of neighbouring C-60(4-) anions. The structure-directing influence of large cations on fulleride structures and the implications for Jahn-Teller distortions of the fulleride anions are discussed.