Lone-Pair-Induced Structural Ordering in the Mixed-Valent 0D Metal-Halides Rb23BiIII x SbIII 7- x SbV 2Cl54 (0 ≤ x ≤ 7)

Bogdan M Benin; Kyle M McCall; Michael Wörle; Dominique Borgeaud; Thomas Vonderach; Kostiantyn Sakhatskyi; Sergii Yakunin; Detlef Günther; Maksym V Kovalenko

doi:10.1021/acs.chemmater.0c04491

Lone-Pair-Induced Structural Ordering in the Mixed-Valent 0D Metal-Halides Rb₂₃Bi^III _x Sb^III _{7- x} Sb^V ₂Cl₅₄ (0 ≤ x ≤ 7)

Chem Mater. 2021 Apr 13;33(7):2408-2419. doi: 10.1021/acs.chemmater.0c04491. Epub 2021 Mar 23.

Authors

Bogdan M Benin^{1

2}, Kyle M McCall^{1

2}, Michael Wörle¹, Dominique Borgeaud¹, Thomas Vonderach¹, Kostiantyn Sakhatskyi^{1

2}, Sergii Yakunin^{1

2}, Detlef Günther¹, Maksym V Kovalenko^{1

2}

Affiliations

¹ Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 1, CH-8093 Zürich, Switzerland.
² Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland.

Abstract

Mixed-valent metal-halides containing ns² lone pairs may exhibit intense visible absorption, while zero-dimensional (0D) ns²-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 Rb₂₃Bi^III _x Sb^III _7-x Sb^V ₂Cl₅₄ (0 ≤ x ≤ 7). Rb₂₃Sb^III ₇Sb^V ₂Cl₅₄ crystallizes in an orthorhombic space group (Cmcm) with a unique, layered 0D structure driven by the arrangement of the 5s² lone pairs of the Sb^IIICl₆ octahedra. This red material is likely the true structure of a previously reported monoclinic "Rb_2.67SbCl₆" phase, the structure of which was not determined. Partially or fully substituting Sb^III with isoelectronic Bi^III yields the series Rb₂₃Bi^III _x Sb^III _7-x Sb^V ₂Cl₅₄ (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 Rb₂₃Bi^III ₇Sb^V ₂Cl₅₄ powder confirms the noncentrosymmetry of this space group. As with the prototypical mixed-valent pnictogen halides, the visible absorption bands of the Rb₂₃Bi^III _x Sb^III _7-x Sb^V ₂Cl₅₄ 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 Rb₂₃Bi^III ₇Sb^V ₂Cl₅₄ exhibits a high resistivity of 1.0 × 10¹⁰ Ω·cm and X-ray photoconductivity with a promising μτ product of 8.0 × 10^-5 cm² s^-1 V^-1. The unique 0D layered structures of the Rb₂₃Bi^III _x Sb^III _7-x Sb^V ₂Cl₅₄ family highlight the versatility of the ns² lone pair in semiconducting metal-halides, pointing the way toward new functional 0D metal-halide compounds.