Lone-Pair-Induced Structural Ordering in the Mixed-Valent 0D Metal-Halides Rb23BiIIIxSbIII7-xSbV2Cl54 (0 ≤ x ≤ 7)

Mixed-valent metal-halides containing ns(2) lone pairs may exhibit intense visible absorption, while zero-dimensional (0D) ns(2)-based metal-chlorides are generally colorless but have demonstrated promising optoelectronic properties suitable for thermometry and radiation detection. Here, we rep ort solvothermally synthesized mixed-valent 0D metal-halides (Rb23BiSb7-xSb2Cl54)-Sb-III-Sb-III-Cl-V (0 <= x <= 7). (Rb23BiSb7-xSb2Cl54)-Sb-III-Sb-III-Cl-V crystallizes in an orthorhombic space group (Cmcm) with a unique, layered 0D structure driven by the arrangement of the 5s(2) lone pairs of the (SPCl6)-Cl-III octahedra. This red material is likely the true structure of a previously reported monoclinic "Rb2.67SbCl6" phase, the structure of which was not determined. Partially or fully substituting Sb(III )with isoelectronic Bi-III yields the series (Rb23BiSb7-xSb2Cl54)-Sb-III-Sb-III-Cl-v (0 < x <= 7), which exhibits a similar layered 0D structure but with additional disorder that yields a trigonal crystal system with an enantiomorphic space group (R32). Second harmonic generation of 532 nm light from a 1064 nm laser using (Rb23BiSb7-xSb2Cl54)-Sb-III-Sb-III-Cl-V powder confirms the noncentrosymmetry of this space group. As with the prototypical mixed-valent pnictogen halides, the visible absorption bands of the (Rb23BiSb7-xSb2Cl54)-Sb-III-Sb-III-Cl-V family are the result of intervalent Sb-III-Sb-v and mixed-valent Bi-III-Sb-v charge transfer bands (CTB), with a blueshift of the absorption edge as Bi-III substitution increases. No PL is observed from this family of semiconductors, but a crystal of (Rb23BiSb7-xSb2Cl54)-Sb-III-Sb-III-Cl-V exhibits a high resistivity of 1.0 x 10(10) Omega.cm and X-ray photoconductivity with a promising mu tau product of 8.0 x 10(-5) cm(2) s(-1) V-1. The unique 0D layered structures of the Rb(23)Bi(III)Sb(7-x)(III)Sb(2)(V)Cl(54)family highlight the versatility of the ns(2) lone pair in semiconducting metal-halides, pointing the way toward new functional 0D metal-halide compounds.