ℇ-RbCuCl3, 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.