Structural insights into a new family of three-dimensional thiocyanate-bridged molecular double perovskites

Abstract

Extending new families of ABX₃-type three-dimensional (3D) molecular perovskites based on diverse X-site molecular ligands is of interest in designing advanced hybrid materials for wide usage. Being a pseudo-halogen ligand, the thiocyanate anion is expected as an X-site bridge to construct 3D molecular perovskites, but has only yielded two pure inorganic instances so far. Herein, we report four new 3D SCN⁻-bridged molecular double perovskites with a general formula of A₂[CdM′(SCN)₆] (A/M′ = K⁺/Ni²⁺, Me₂NH₂⁺/Ni²⁺, Me₂NH₂⁺/Mn²⁺, Me₃S⁺/Cd²⁺), including three unprecedented hybrid instances incorporating organic cations. A detailed comparison between these SCN⁻-bridged molecular perovskites and some azido-bridged analogues, on their host–guest interactions and structural distortions, revealed that the bent Cd–S–C angles in these SCN⁻-bridged molecular perovskites vary in a narrow range, endowing their frameworks with a high structural distortion and a relatively strong structural rigidity. The present study not only extends SCN⁻-bridged 3D molecular perovskites to enrich the perovskite family, but also paves a way for the rational design of new molecular perovskites.