Divergent Optical Properties in an Isomorphous Family of Multinary Iodido Pentelates

Discrete Hexa- and Binuclear Heterometallic Iodobismuthate(III) Complexes with Cu(I) and Ag(I)

The rare examples of discrete anionic halobismuthates(III) with group 11 elements were obtained. Those are (3-MePyH)6[Bi4Cu2I20] (1) and (3,5-MePyC6)3[BiAgI7]2 (2) (3-MePyH = 3-methylpyridinium cation, 3,5-MePyC6=1,6-bis(3,5-dimethylpyridinium)hexane dication). Both complexes were isolated as pure phases; the optical band gaps for 1 and 2 are 1.75 and 2.23 eV, respectively.

Ternary Complexes of BiI3/CuI and SbI3/CuI with Tetrahydrothiophene

Reactions of BiI3/CuI mixtures with tetrahydrothiophene (THT) in toluene produce 2-D sheet networks BiCu3I6(THT)n (n = 2, 3, or 4), depending on reaction conditions. All three structures are based on BiI6 octahedra, which share pairs of (μ2-I)2 with Cu3(THT)n units. BiCu3I6(THT)2 features Cu2(μ2-I)2 rhombs with close Cu···Cu interactions and is accompanied by formation of the very complex HBi3Cu12I22(THT)8. Reactions of SbI3/CuI with THT in toluene produced a SbCu3I6(THT)2 network shows Cu3(μ2-THT)2 units, like its Bi congener, but Cu6(μ2-I)6 barrels rather than rhombs. Isolated SbI3 units are stacked above the Cu6I6 barrels. A molecular compound, Sb3Cu3I12(THT)6 consists of a face-sharing Sb3I12 stack, in which the Cu-THT units are bonded in asymmetric fashion about the central SbI6. Metal-halide bonds were investigated via QTAIM and NLMO analyses, demonstrating that these bonds are largely ionic and occur between the Bi/Sb and I p orbitals. Hirshfeld analysis shows significant H···H and H···I interactions. Diffuse reflectance spectroscopy (DRS) reveals band edges for the Bi species of 1.71-1.82 eV, while those for the neutral Sb complexes are in the range of 1.94-2.06 eV. Mapping of the electronic structure via density of state calculations indicates population of antibonding Bi/Sb-I orbitals in the excited state.

Copper and silver heterometallic iodoantimonates: structure, thermal stability, and optical properties

Seven heterometallic iodoantimonates with the general formula (Cat)2{[Sb2M2I10]} (M = Cu(I) (1-6), Ag(I) (7)) were prepared. X-ray diffraction data indicate that these compounds are the first Sb(III) representatives of the structural type previously known only for heterometallic iodobismuthates(III). In 3 and 4, halogen-substituted cations form halogen bonds with the heterometallic halometalate chain. 1-7 show prominent thermal stability. The estimated optical band gaps lie between 2.16 and 2.40 eV. As in heterometallic iodobismuthates, incorporation of Cu+ rather than Ag+ provides a much lower band gap.

Copper- and Silver-Containing Heterometallic Iodobismuthates: Features of Thermochromic Behavior

Nine heterometallic iodobismuthates with the general formula Cat₂{[Bi₂M₂I₁₀}] (M = Cu(I), Ag(I), Cat = organic cation) were synthesized. According to X-ray diffraction data, their crystal structures consisted of {Bi₂I₁₀} units interconnected with Cu(I) or Ag(I) atoms through I-bridging ligands, forming one-dimensional polymers. The compounds are thermally stable up to 200 °C. Optical band gaps (E_g), estimated at room temperature via diffuse reflectance measurements, range from 1.81 to 2.03 eV. Thermally induced changes in optical behavior (thermochromism) for compounds 1-9 were recorded, and general correlations were established. The thermal dependence of E_g appears to be close to linear for all studied compounds.

Supramolecular Diiodine-Bromostannate(IV) Complexes: Narrow Bandgap Semiconductors

Three supramolecular bromostannates(IV) with "trapped" diiodine molecules, Cat₂{[SnBr₆](I₂)} (Cat = Me₄N⁺ (1), 1-MePy⁺ (2) and 4-MePyH (3)), were synthesized. In all cases, I₂ linkers are connected with bromide ligands via halogen···halogen non-covalent interactions. Articles 1-3 were studied using Raman spectroscopy, thermogravimetric analysis, and diffuse reflectance spectroscopy. The latter indicates that 1-3 are narrow band gap semiconductors.

The influence of copper on the optical band gap of heterometallic iodido antimonates and bismuthates

Halogenido metalates of heavy main group elements are versatile semiconductor materials with broad applications. Especially the iodido metalates generally show small optical band gaps, making them suitable for photovoltaics. However, the most promising results have been generated using toxic lead-based materials, raising environmental concerns, while the related and far less toxic bismuth compounds show band gaps too large for direct use in photovoltaics. The introduction of heterometals such as copper can significantly lower the band gap of iodido bismuthates and antimonates, but no clear trend could yet be established in this regard. In this work a short overview over all known copper iodido bismuthates and antimonates is given and this small family of compounds is expanded with nine charged as well as neutral complexes [E_kM_lI_m(P(R)₃)_n]^q- (E = Sb, Bi; M = Cu, Ag; R = Ph, o-tol). The compounds' crystal structures, stability and optical properties are investigated and compared to the findings of quantum chemical investigations. The main excitation is shown to be a copper to antimony or copper to bismuth charge transfer while the relative energetic position of the organic ligand orbitals influences the magnitude of the band gap. This reveals that the nature of the ligands and the coordination environment at the copper atom is crucial for designing new copper iodido antimonates and bismuthates with specific band gaps.

Multiple Roles of 1,4-Diazabicyclo[2.2.2]octane in the Solvothermal Synthesis of Iodobismuthates

Hybrid bismuth-containing halides are emerging as alternative candidates to lead-containing perovskites for light-harvesting applications, as Bi3+ is isoelectronic with Pb2+ and the presence of an active lone pair of electrons is expected to result in outstanding charge-carrier transport properties. Here, we report a family of one binary and three ternary iodobismuthates containing 1,4-diazabicyclo[2.2.2]octane (DABCO). These materials have been prepared solvothermally and their crystal structures, thermal stability, and optical properties determined. Reactions carried out in the presence of bismuth iodide and DABCO produced (C6H12N2)BiI3 (1), which consists of hybrid ribbons in which pairs of edge-sharing bismuth octahedra are linked by DABCO ligands. Short I···I contacts give rise to a three-dimensional network. Similar reactions in the presence of copper iodide produced (C8H17N2)2Bi2Cu2I10 (2) and [(C6H13N2)2BiCu2I7](C2H5OH) (3) in which either ethylated DABCO cations (EtDABCO)+ or monoprotonated DABCO cations (DABCOH)+ are coordinated to copper in discrete tetranuclear and trinuclear clusters, respectively. In the presence of potassium iodide, a unique three-dimensional framework, (C6H14N2)[(C6H12N2)KBiI6] (4), was formed, which contains one-dimensional hexagonal channels approximately 6 Å in diameter. The optical band gaps of these materials, which are semiconductors, range between 1.82 and 2.27 eV, with the lowest values found for the copper-containing discrete clusters. Preliminary results on the preparation of thin films are presented.

Unexpected Polymorphism in Bromoantimonate(III) Complexes and Its Effect on Optical Properties

Reactions of [SbBr₆]^3- containing HBr solutions with bromide salts of 1,1'-(1,2-ethanediyl)bis(pyridine) (PyC₂²⁺) or 1,1'-(1,2-ethanediyl)bis(3,5-dimethylpyridine) (3,5-MePyC₂²⁺) initially result in the formation of the deep orange complexes Cat[SbBr₅] (1 and 2), featuring unusual Sb···Br interactions in the solid state. In the mother liquor, 1 transforms into discrete binuclear (C₂Py)₂[Sb₂Br₁₀], which demonstrates polymorphism (triclinic 3 and monoclinic 4), while 2 transforms into polymeric (3,5-MePy){[SbBr₄]} (5). DFT calculations reveal that the system of noncovalent Sb···Br contacts may be responsible for the appearance of the observed optical properties (unusual deep orange coloring).

Mixed Group 14–15 Metalates as Model Compounds for Doped Lead Halide Perovskites

Doping and alloying are valuable tools for modifying and enhancing the properties and performance of lead halide perovskites. However, the effects of heterovalent doping with Sb³⁺ and Bi³⁺ cations are still a matter of current investigation. Due to the different charge of the dopants compared to the constituting Pb²⁺ ions, a simultaneous creation of defects is unavoidable and the influence of these defects and the actual metal substitution become entangled. Herein, we present the first 14–15 iodido metalates, (BED)₄PbE₂I₁₆ (BED=N‐benzylethylenediammonium; E=Sb (1), Bi (2)), which are model compounds for doped lead iodide perovskites and display surprisingly low band gaps of 2.01 (1) and 1.88 eV (2). Quantum chemical investigations show that this stems from a good electronic match between the PbI₆ and EI₆ units of the compounds. Our results provide a model system for doped perovskites, but also represent the first examples of a promising new class of metal halide materials.

One-Dimensional Diiodine-Iodobismuthate(III) Hybrids Cat3{[Bi2I9](I2)3}: Syntheses, Stability, and Optical Properties

One-dimensional iodine-rich iodobismuthates(III), Cat₃{[Bi₂I₉](I₂)₃} [Cat = 1,4-MePy (1) and 1-EtBMAP (2)], feature the highest amount of "trapped" diiodine units in polyhalogen-halometalates of p-block elements. Both complexes have narrow optical band gaps (1.55 and 1.63 eV, respectively) and moderate thermal stability.

Dibismuthates as Linking Units for Bis-Zwitterions and Coordination Polymers

Adducts of bismuth trihalides BiX₃ (X = Cl, Br, I) and the PS₃ ligand (PS₃ = P(C₆H₄-o-CH₂SCH₃)₃) react with HCl to form inorganic/organic hybrids with the general formula [HPS₃BiX₄]₂. On the basis of their solid-state structures determined by single-crystal X-ray diffraction, these compounds exhibit discrete bis-zwitterionic assemblies consisting of two phosphonium units [HPS₃]⁺ linked to a central dibismuthate core [Bi₂X₈]^2– via S→Bi dative interactions. Remarkably, the phosphorus center of the PS₃ ligand undergoes protonation with hydrochloric acid. This is in stark contrast to the protonation of phosphines commonly observed with hydrogen halides resulting in equilibrium. To understand the important factors in this protonation reaction, ³¹P NMR experiments and DFT computations have been performed. Furthermore, the dibismuthate linker was utilized to obtain the coordination polymer {[AgPS₃BiCl₃(OTf)]₂(CH₃CN)₂}_∞, in which dicationic [Ag(PS₃)]₂²⁺ macrocycles containing five-coordinate silver centers connect the dianionic [Bi₂Cl₆(OTf)₂]^2– dibismuthate fragments. The bonding situation in these dibismuthates has been investigated by single-crystal X-ray diffraction and DFT calculations (NBO analysis, AIM analysis, charge distribution).

The potential of dibismuthates [Bi₂X₈]²⁻ as building blocks for the synthesis of bis-zwitterions and coordination polymers has been shown. The structures of these compounds and the bonding in the dibismuthate linkers have been studied by single-crystal X-ray diffraction and DFT calculations.

(HPy)2(Py)CuBi3I12, a low bandgap metal halide photoconductor

Bismuth halides represent an emergent class of materials that combines semiconductor properties with non-toxic constituents. However, many simple bismuth halide compounds feature bandgaps that are significantly higher than those of the lead halide perovskites, which they are supposed to replace. One way to address this issue is the preparation of multinary metal halide materials that feature an additional metal ion. Here, we report on the synthesis and properties of (HPy)2(Py)CuBi3I12 (1) a new copper iodido bismuthate, a photoconductor, which shows a low band gap of 1.59 eV and good thermal and air stability.