The introduction of chirality in lead halide perovskites and related metal halide materials allows for an expansion of their unique and useful properties toward nonlinear optics. However, when synthesizing materials based on less toxic metals antimony and bismuth, the large variability in the crystal structures of their metalates and their tendency to form molecular or chainlike anion motifs can be a challenge when creating tunable materials. Here, we show that using a chiral amine template, we can synthesize an isomorphous family of compoundsand Bi; X = Cl, Br, and I) that combines multiple aspects: the compounds are not only chiral but also feature a trilayered arrangement of cations and anions that allows for facile cleavage and exfoliation. The different combinations of E and X allow for a variation of the onset of absorption between 3.35 and 2.09 eV. Using femtosecond laser spectroscopy, we show that our materials allow for efficient second-harmonic generation. Together with a simple synthesis and good stability, this makes these materials promising candidates for linear and nonlinear optical devices.
Two new, isostructural members of the title material class, [PPh][CuBiI] (1) and [PPh][AgBiI] (2), have been prepared via a facile solution route. The crystal structure of both compounds features a tetranuclear [MBiI] (M = Cu, Ag) anion that displays an unprecedented face-sharing mode of connection between BiI octahedra and MI tetrahedra, enabling close Bi···M contacts. The two compounds allow for a direct experimental and quantum chemical investigation of the influence of group 11 metal cations on the optical and electronic properties of ternary iodido bismuthate anions, indicating that Cu is a better electronic match than Ag, resulting in a significantly lower optical band gap of the copper compound.
Multinary organic−inorganic metal halide materials beyond the perovskite motif can help to address both fundamental aspects such as the electronic interactions between different metalate building units and practical issues like stability and ease of preparation in this new field of research. However, such multinary compounds have remained quite rare for the halogenido pentelates, as the formation of simpler side phases can be a significant hindrance. Here, we report a family o f f o u r n e w m u l t i n a r y i o d i d o p e n t e l a t e s [PPh 4 ] 2 [ECu 2 I 7 (nitrile)] (E = Sb, Bi; nitrile = acetonitile or propionitrile), including the first metalate with a Cu−I−Sb unit. The compounds can be obtained by facile solution or mechanochemical methods and display good stability up to 160 °C. A comparison with compounds containing binary anions [EI 6 ] 3− reveals that, unexpectedly, the addition of the iodido cuprate unit causes a blue-shift in the absorption of the antimonates but a red-shift in the bismuthates. Photoluminescence investigations at 10 K show that the compounds display broad luminescence bands that correspond well with the trend in their onset of absorption. Overall, the work highlights that multinary, non-perovskite halogenido metalates can be a valuable expansion of the chemistry of metal halide perovskites.
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