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1. Observation of Transition‐Metal–Boron Triple Bonds in IrB ₂ O ⁻ and ReB ₂ O ⁻

   https://doi.org/10.1002/anie.202006652  

   Chen, Teng‐Teng; Cheung, Ling Fung; Chen, Wei‐Jia; Cavanagh, Joseph; Wang, Lai‐Sheng (June 2020, Angewandte Chemie International Edition)

   Abstract Multiple bonds between boron and transition metals are known in many borylene (:BR) complexes via metal d_π→BR back‐donation, despite the electron deficiency of boron. An electron‐precise metal–boron triple bond was first observed in BiB₂O⁻[Bi≡B−B≡O]⁻in which both boron atoms can be viewed as sp‐hybridized and the [B−BO]⁻fragment is isoelectronic to a carbyne (CR). To search for the first electron‐precise transition‐metal‐boron triple‐bond species, we have produced IrB₂O⁻and ReB₂O⁻and investigated them by photoelectron spectroscopy and quantum‐chemical calculations. The results allow to elucidate the structures and bonding in the two clusters. We find IrB₂O⁻has a closed‐shell bent structure (C_s,¹A′) with BO⁻coordinated to an Ir≡B unit, (⁻OB)Ir≡B, whereas ReB₂O⁻is linear (C_∞v,³Σ⁻) with an electron‐precise Re≡B triple bond, [Re≡B−B≡O]⁻. The results suggest the intriguing possibility of synthesizing compounds with electron‐precise M≡B triple bonds analogous to classical carbyne systems. 

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2. Synthesis of TlBr and Tl ₂ AgBr ₃ Nanocrystals

   https://doi.org/10.1002/cnma.202000100  

   Siegler, Timothy_D; Shah, Tushti; Houck, Daniel_W; Suri, Mokshin; Zhang, Yangning; Korgel, Brian_A (March 2020, ChemNanoMat)

   Abstract There are only a few examples of nanocrystal synthesis with thallium (Tl). Here, we report the synthesis of uniform, ligand‐stabilized colloidal nanocrystals of TlBr and Tl₂AgBr₃nanocrystals with average diameter ranging between 10 and 20 nm. TlBr nanocrystals are made by hot injection of trimethylsilyl bromide (TMSBr) into solutions of oleylamine, oleic acid and octadecene with thallium (III) or thallium (I) acetate. Tl₂AgBr₃nanocrystals form when silver (I) acetate is included in the reaction. The TlBr nanocrystals have CsCl crystal structure with a direct band gap of 3.1 eV. The Tl₂AgBr₃nanocrystals have trigonal dolomite crystal structure with an indirect band gap of 3.1 eV. The TlBr nanocrystals made with thallium (III) were sufficiently uniform to assemble into face‐centered cubic (fcc) superlattices. 

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3. Integration of Highly Luminescent Lead Halide Perovskite Nanocrystals on Transparent Lead Halide Nanowire Waveguides through Morphological Transformation and Spontaneous Growth in Water

   https://doi.org/10.1002/smll.202105009  

   Chen, Tao; Wang, Chong; Xing, Xinxin; Qin, Zhaojun; Qin, Fan; Wang, Yanan; Alam, Md Kamrul; Hadjiev, Viktor G.; Yang, Guang; Ye, Shuming; et al (January 2022, Small)

   Abstract The integration of highly luminescent CsPbBr₃quantum dots on nanowire waveguides has enormous potential applications in nanophotonics, optical sensing, and quantum communications. On the other hand, CsPb₂Br₅nanowires have also attracted a lot of attention due to their unique water stability and controversial luminescent property. Here, the growth of CsPbBr₃nanocrystals on CsPb₂Br₅nanowires is reported first by simply immersing CsPbBr₃powder into pure water, CsPbBr_3−γ X_γ(X = Cl, I) nanocrystals on CsPb₂Br_5−γ X_γnanowires are then synthesized for tunable light sources. Systematic structure and morphology studies, including in situ monitoring, reveal that CsPbBr₃powder is first converted to CsPb₂Br₅microplatelets in water, followed by morphological transformation from CsPb₂Br₅microplatelets to nanowires, which is a kinetic dissolution–recrystallization process controlled by electrolytic dissociation and supersaturation of CsPb₂Br₅. CsPbBr₃nanocrystals are spontaneously formed on CsPb₂Br₅nanowires when nanowires are collected from the aqueous solution. Raman spectroscopy, combined photoluminescence, and SEM imaging confirm that the bright emission originates from CsPbBr_3−γ X_γnanocrystals while CsPb₂Br_5−γ X_γnanowires are transparent waveguides. The intimate integration of nanoscale light sources with a nanowire waveguide is demonstrated through the observation of the wave guiding of light from nanocrystals and Fabry–Perot interference modes of the nanowire cavity. 

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4. Probing the Nature of the Transition-Metal-Boron Bonds and Novel Aromaticity in Small Metal-Doped Boron Clusters Using Photoelectron Spectroscopy

   https://doi.org/10.1146/annurev-physchem-082820-113041  

   Chen, Teng-Teng; Cheung, Ling Fung; Wang, Lai-Sheng (April 2022, Annual Review of Physical Chemistry)

   Photoelectron spectroscopy combined with quantum chemistry has been a powerful approach to elucidate the structures and bonding of size-selected boron clusters (B n − ), revealing a prevalent planar world that laid the foundation for borophenes. Investigations of metal-doped boron clusters not only lead to novel structures but also provide important information about the metal-boron bonds that are critical to understanding the properties of boride materials. The current review focuses on recent advances in transition-metal-doped boron clusters, including the discoveries of metal-boron multiple bonds and metal-doped novel aromatic boron clusters. The study of the RhB − and RhB 2 O − clusters led to the discovery of the first quadruple bond between boron and a transition-metal atom, whereas a metal-boron triple bond was found in ReB 2 O − and IrB 2 O − . The ReB 4 − cluster was shown to be the first metallaborocycle with Möbius aromaticity, and the planar ReB 6 − cluster was found to exhibit aromaticity analogous to metallabenzenes. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 73 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates. 

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5. Phase‐Controlled Synthesis and Quasi‐Static Dielectric Resonances in Silver Iron Sulfide (AgFeS ₂ ) Nanocrystals

   https://doi.org/10.1002/smll.202104975  

   Lee, Soohyung; Hoyer, Chad E.; Liao, Can; Li, Xiaosong; Holmberg, Vincent C. (December 2021, Small)

   Abstract Ternary metal‐chalcogenide semiconductor nanocrystals are an attractive class of materials due to their tunable optoelectronic properties that result from a wide range of compositional flexibility and structural diversity. Here, the phase‐controlled synthesis of colloidal silver iron sulfide (AgFeS₂) nanocrystals is reported and their resonant light–matter interactions are investigated. The product composition can be shifted selectively from tetragonal to orthorhombic by simply adjusting the coordinating ligand concentration, while keeping the other reaction parameters unchanged. The results show that excess ligands impact precursor reactivity, and consequently the nanocrystal growth rate, thus deterministically dictating the resulting crystal structure. Moreover, it is demonstrated that the strong ultraviolet‐visible extinction peak exhibited by AgFeS₂nanocrystals is a consequence of a quasi‐static dielectric resonance (DR), analogous to the optical response observed in CuFeS₂nanocrystals. Spectroscopic studies and computational calculations confirm that a negative permittivity at ultraviolet/visible frequencies arises due to the electronic structure of these intermediate‐band (IB) semiconductor nanocrystals, resulting in a DR consisting of resonant valence‐band‐to‐intermediate‐band excitations, as opposed to the well‐known localized surface plasmon resonance response typically observed in metallic nanostructures. Overall, these results expand the current library of an underexplored class of IB semiconductors with unique optical properties, and also enrich the understanding of DRs in ternary metal‐iron‐sulfide nanomaterials. 

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