Crystal structures and luminescence properties of halocuprates with trimethylsulfonium cations

Abstract

We report the crystal structures, thermal stability, and luminescence properties of three trimethylsulfonium halocuprates: (TMS)Cu₂I₃, and two new bromide phases: (TMS)Cu₂Br₃ and (TMS)₂CuBr₃. (TMS)Cu₂I₃ and (TMS)Cu₂Br₃ are isostructural and contain double chains of edge-sharing [CuX₄] tetrahedra, whereas (TMS)₂CuBr₃ features isolated [CuBr₃]²⁻ triangular units. All compounds exhibit direct bandgaps and demonstrate photoluminescence at low temperature, with (TMS)Cu₂Br₃ demonstrating temperature-dependent dual emission behavior, observed for the first time among related hybrid halocuprates. Through comparative analysis of optical properties with structurally related halocuprates and DFT calculations, we elucidate the structure–property relationships governing the observed luminescence behavior of ACu₂X₃-type halocuprates.