Coordination engineering in antimony-based hybrid crystals toward highly efficient green emission

Zero-dimensional organic-inorganic hybrid metal halides have emerged as promising luminescent materials with structural diversity and tunable emission properties. However, it remains challenging to precisely control the metal coordination environment to suppress non-radiative recombination and improve the photoluminescence quantum yield (PLQY). Herein, we report an acid-solvent synergistic strategy that enables stepwise evolution of Sb coordination environments in hybrid halides. The non-emissive phase (H₂PIP)[SbCl₅]·H₂O (1, PIP = piperazine), composed of edge-sharing [Sb₂Cl₁₀]^4- dimers, transforms into an orange-emitting intermediate (H₂PIP)₅(H₅O₂)[SbCl₅]₂[SbCl₆]Cl₄ (2) with mixed discrete polyhedra, in the presence of HCl. Upon CH₃CN incorporation, the mixed Sb coordination polyhedra transform into isolated [SbCl₆]^3- octahedra in green-emitting compound (H₂PIP)₂(NH₄)[SbCl₆]Cl₂·CH₃CN (3). Accompanying this evolution of coordination environments, the PLQY rises from <1% to 23.6% for the intermediate and ultimately reaches 90.4%. The enhanced PLQY originates from the expanded Sb⋯Sb distance and significant [SbCl₆]^3- octahedral distortion, which facilitate the formation and radiative recombination of self-trapped excitons. This work provides insights into acid-solvent directed coordination engineering for highly efficient Sb-based hybrid emitters.