ϵ-RbCuCl3, a new polymorph of rubidium copper trichloride: synthesis, structure and structural complexity

A novel polymorph of RbCuCl 3 (rubidium copper trichloride), denoted ∊-RbCuCl 3 , has been prepared by chemical vapour transport (CVT) from a mixture of CuO, CuCl 2 , SeO 2 and RbCl. The new polymorph crystallizes in the orthorhombic space group C 222 1 . The crystal structure is based on an octahedral framework of the 4 H perovskite type. The Rb + and Cl − ions form a four-layer closest-packing array with an ABCB sequence. The Cu 2+ cations reside in octahedral cavities with a typical [4 + 2]-Jahn–Teller-distorted coordination, forming four short and two long Cu—Cl bonds. ∊-RbCuCl 3 is the most structurally complex and most dense among all currently known RbCuCl 3 polymorphs, which allows us to suggest that it is a high-pressure phase, which is unstable under ambient conditions.