Lone-Pair-Induced Structural Ordering in the Mixed-Valent 0D Metal-Halides RbBi Sb Sb Cl (0 ≤ ≤ 7).

Mixed-valent metal-halides containing s lone pairs may exhibit intense visible absorption, while zero-dimensional (0D) s-based metal-chlorides are generally colorless but have demonstrated promising optoelectronic properties suitable for thermometry and radiation detection. Here, we report solvothermally synthesized mixed-valent 0D metal-halides RbBi Sb Sb Cl (0 ≤ ≤ 7). RbSb Sb Cl crystallizes in an orthorhombic space group () with a unique, layered 0D structure driven by the arrangement of the 5s lone pairs of the SbCl octahedra. This red material is likely the true structure of a previously reported monoclinic "RbSbCl" phase, the structure of which was not determined. Partially or fully substituting Sb with isoelectronic Bi yields the series RbBi Sb Sb Cl (0 < ≤ 7), which exhibits a similar layered 0D structure but with additional disorder that yields a trigonal crystal system with an enantiomorphic space group (32). Second harmonic generation of 532 nm light from a 1064 nm laser using RbBi Sb Cl powder confirms the noncentrosymmetry of this space group. As with the prototypical mixed-valent pnictogen halides, the visible absorption bands of the RbBi Sb Sb Cl family are the result of intervalent Sb-Sb and mixed-valent Bi-Sb charge transfer bands (CTB), with a blueshift of the absorption edge as Bi substitution increases. No PL is observed from this family of semiconductors, but a crystal of RbBi Sb Cl exhibits a high resistivity of 1.0 × 10 Ω·cm and X-ray photoconductivity with a promising μτ product of 8.0 × 10 cm s V. The unique 0D layered structures of the RbBi Sb Sb Cl family highlight the versatility of the s lone pair in semiconducting metal-halides, pointing the way toward new functional 0D metal-halide compounds.