ℇ-RbCuCl 3 , a new polymorph of rubidium copper trichloride: synthesis, structure and structural complexity.

A novel polymorph of RbCuCl3 (rubidium copper trichloride), denoted ℇ-RbCuCl3 , has been prepared by chemical vapour transport (CVT) from a mixture of CuO, CuCl2 , SeO2 and RbCl. The new polymorph crystallizes in the orthorhombic space group C2221 . The crystal structure is based on an octahedral framework of the 4H perovskite type. The Rb+ and Cl- ions form a four-layer closest-packing array with an ABCB sequence. The Cu2+ cations reside in octahedral cavities with a typical [4 + 2]-Jahn-Teller-distorted coordination, forming four short and two long Cu-Cl bonds. ℇ-RbCuCl3 is the most structurally complex and most dense among all currently known RbCuCl3 polymorphs, which allows us to suggest that it is a high-pressure phase, which is unstable under ambient conditions.