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1. Mosaic Cu I −Cu II −In III 2D Perovskites: Pressure‐Dependence of the Intervalence Charge Transfer and a Mechanochemical Alloying Method

   https://doi.org/10.1002/ange.202300957  

   Li, Jiayi ; Matheu, Roc ; Ke, Feng ; Liu, Zhenxian ; Lin, Yu ; Karunadasa, Hemamala I. ( April 2023 , Angewandte Chemie)

   The perovskite (BA)₄[Cu^II(Cu^IIn^III)_0.5]Cl₈(1_BA; BA⁺=butylammonium) allows us to study the high‐pressure structural, optical, and transport properties of a mixed‐valence 2D perovskite. Compressing1_BAreduces the onset energy of Cu^I/IIintervalence charge transfer from 1.2 eV at ambient pressure to 0.2 eV at 21 GPa. The electronic conductivity of1_BAincreases by 4 orders of magnitude upon compression to 20 GPa, when the activation energy for conduction decreases to 0.16 eV. In contrast, Cu^IIperovskites achieve similar conductivity at ≈50 GPa. The solution‐state synthesis of these perovskites is complicated, with more undesirable side products likely from the precursor mixtures containing three different metal ions. To circumvent this problem, we demonstrate an efficient mechanochemical synthesis to expand this family of halide perovskites with complex composition by simply pulverizing together powders of 2D Cu^IIsingle perovskites and Cu^IIn^IIIdouble perovskites.

    

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2. Uncovering a CF 3 Effect on X‐ray Absorption Energies of [Cu(CF 3 ) 4 ] − and Related Copper Compounds by Using Resonant Diffraction Anomalous Fine Structure (DAFS) Measurements**

   https://doi.org/10.1002/ange.202313744  

   Alayoglu, Pinar ; Chang, Tieyan ; Yan, Connly ; Chen, Yu‐Sheng ; Mankad, Neal P. ( November 2023 , Angewandte Chemie)

   Understanding the electronic structures of high‐valent metal complexes aids the advancement of metal‐catalyzed cross coupling methodologies. A prototypical complex with formally high valency is [Cu(CF₃)₄]⁻(1), which has a formal Cu(III) oxidation state but whose physical analysis has led some to a Cu(I) assignment in an inverted ligand field model. Recent examinations of1by X‐ray spectroscopies have led previous authors to contradictory conclusions, motivating the re‐examination of its X‐ray absorption profile here by a complementary method, resonant diffraction anomalous fine structure (DAFS). From analysis of DAFS measurements for a series of seven mononuclear Cu complexes including1, here it is shown that there is a systematic trifluoromethyl effect on X‐ray absorption that blue shifts the resonant Cu K‐edge energy by 2–3 eV per CF₃, completely accounting for observed changes in DAFS profiles between formally Cu(III) complexes like1and formally Cu(I) complexes like (Ph₃P)₃CuCF₃(3). Thus, in agreement with the inverted ligand field model, the data presented herein imply that1is best described as containing a Cu(I) ion with dⁿcount approaching 10.

    

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3. Uncovering a CF 3 Effect on X‐ray Absorption Energies of [Cu(CF 3 ) 4 ] − and Related Copper Compounds by Using Resonant Diffraction Anomalous Fine Structure (DAFS) Measurements**

   https://doi.org/10.1002/anie.202313744  

   Alayoglu, Pinar ; Chang, Tieyan ; Yan, Connly ; Chen, Yu‐Sheng ; Mankad, Neal P. ( November 2023 , Angewandte Chemie International Edition)

   Understanding the electronic structures of high‐valent metal complexes aids the advancement of metal‐catalyzed cross coupling methodologies. A prototypical complex with formally high valency is [Cu(CF₃)₄]⁻(1), which has a formal Cu(III) oxidation state but whose physical analysis has led some to a Cu(I) assignment in an inverted ligand field model. Recent examinations of1by X‐ray spectroscopies have led previous authors to contradictory conclusions, motivating the re‐examination of its X‐ray absorption profile here by a complementary method, resonant diffraction anomalous fine structure (DAFS). From analysis of DAFS measurements for a series of seven mononuclear Cu complexes including1, here it is shown that there is a systematic trifluoromethyl effect on X‐ray absorption that blue shifts the resonant Cu K‐edge energy by 2–3 eV per CF₃, completely accounting for observed changes in DAFS profiles between formally Cu(III) complexes like1and formally Cu(I) complexes like (Ph₃P)₃CuCF₃(3). Thus, in agreement with the inverted ligand field model, the data presented herein imply that1is best described as containing a Cu(I) ion with dⁿcount approaching 10.

    

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4. Small‐Band‐Gap Halide Double Perovskites

   https://doi.org/10.1002/anie.201807421  

   Slavney, Adam H. ; Leppert, Linn ; Saldivar Valdes, Abraham ; Bartesaghi, Davide ; Savenije, Tom J. ; Neaton, Jeffrey B. ; Karunadasa, Hemamala I. ( August 2018 , Angewandte Chemie International Edition)

   Despite their compositional versatility, most halide double perovskites feature large band gaps. Herein, we describe a strategy for achieving small band gaps in this family of materials. The new double perovskites Cs₂AgTlX₆(X=Cl (1) and Br (2)) have direct band gaps of 2.0 and 0.95 eV, respectively, which are approximately 1 eV lower than those of analogous perovskites. To our knowledge, compound2displays the lowest band gap for any known halide perovskite. Unlike in A^IB^IIX₃perovskites, the band‐gap transition in A^I₂BB′X₆double perovskites can show substantial metal‐to‐metal charge‐transfer character. This band‐edge orbital composition is used to achieve small band gaps through the selection of energetically aligned B‐ and B′‐site metal frontier orbitals. Calculations reveal a shallow, symmetry‐forbidden region at the band edges for1, which results in long (μs) microwave conductivity lifetimes. We further describe a facile self‐doping reaction in2through Br₂loss at ambient conditions.

    

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5. Small‐Band‐Gap Halide Double Perovskites

   https://doi.org/10.1002/ange.201807421  

   Slavney, Adam H. ; Leppert, Linn ; Saldivar Valdes, Abraham ; Bartesaghi, Davide ; Savenije, Tom J. ; Neaton, Jeffrey B. ; Karunadasa, Hemamala I. ( August 2018 , Angewandte Chemie)

   Despite their compositional versatility, most halide double perovskites feature large band gaps. Herein, we describe a strategy for achieving small band gaps in this family of materials. The new double perovskites Cs₂AgTlX₆(X=Cl (1) and Br (2)) have direct band gaps of 2.0 and 0.95 eV, respectively, which are approximately 1 eV lower than those of analogous perovskites. To our knowledge, compound2displays the lowest band gap for any known halide perovskite. Unlike in A^IB^IIX₃perovskites, the band‐gap transition in A^I₂BB′X₆double perovskites can show substantial metal‐to‐metal charge‐transfer character. This band‐edge orbital composition is used to achieve small band gaps through the selection of energetically aligned B‐ and B′‐site metal frontier orbitals. Calculations reveal a shallow, symmetry‐forbidden region at the band edges for1, which results in long (μs) microwave conductivity lifetimes. We further describe a facile self‐doping reaction in2through Br₂loss at ambient conditions.

    

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