Establishing Family Relations in Group 15 Halogenido Metalates with the Largest Molecular Antimony Iodide Anion

Studying structurally related families of compounds is a valuable tool in understanding and predicting material properties and has been extensively used for metal halide perovskites. Due to the variable anion structures in group 15 halogenido metalates, similar family relations are still largely missing. Herein, we present compounds featuring the [Sb_2n I_6n+4 ]^4- family of anions, including the first n=5 member in [Hpyz]₄ [Sb₁₀ I₃₄ ] (Hpyz=pyrazinium), which contains the largest halogenido pentelate anion reported to date. The optical properties of compounds featuring n=1-5 anions show a clear trend as well as an outlier, a low band gap of 1.72 eV for [Hpyz]₄ [Sb₁₀ I₃₄ ], that can be well understood using quantum chemical investigations. Also using SbI₃ and [H₂ NMe₂ ]₃ [SbI₆ ], a compound featuring a single octahedral [SbI₆ ]^3- unit, as limiting cases, we show that structure-property relationships can be established in group 15 halogenido metalates in a similar way as in metal halide perovskites, thus providing a framework for understanding new and known compounds in this emerging class of materials.