Cs4C60: single phase synthesis and orientational order

Abstract

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) A₄C₆₀ structure found for K₄C₆₀ and Rb₄C₆₀ , due to the orientational ordering of the C₆₀^4– 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 C₆₀^4– anions. The structure-directing influence of large cations on fulleride structures and the implications for Jahn–Teller distortions of the fulleride anions are discussed.