?‐RbCuCl 3 3 , a new polymorph of rubidium copper trichloride: synthesis, structure and structural complexity

摘要

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.