The Structures of the Group 15 Element(III) Halides and Halogenoanions

Photophysical properties of tetrabutylammonium metal chlorides with different inorganic frameworks

The luminescence of single crystals of (TBA)PbCl₃, (TBA)₂Sb₂Cl₈, (TBA)₃Bi₂Cl₉ and (TBA)SnCl₅·2EtOH (TBA = tetrabutylammonium, EtOH = Ethanol) synthsized were assigned distinctively to the centres of self-trapped excitons (STEs), TBA⁺, TBA⁺ and co-emission of STEs and TBA⁺. This work demonstrates that organic cations without benzene or aromatic rings can also be used as the sole luminescence centres for metal halides.

Establishing Family Relations in Group 15 Halogenido Metalates with the Largest Molecular Antimony Iodide Anion

Studying structurally related families of compounds is a valuable tool in understanding and predicting material properties and has been extensively used for metal halide perovskites. Due to the variable anion structures in group 15 halogenido metalates, similar family relations are still largely missing. Herein, we present compounds featuring the [Sb_2n I_6n+4 ]^4- family of anions, including the first n=5 member in [Hpyz]₄ [Sb₁₀ I₃₄ ] (Hpyz=pyrazinium), which contains the largest halogenido pentelate anion reported to date. The optical properties of compounds featuring n=1-5 anions show a clear trend as well as an outlier, a low band gap of 1.72 eV for [Hpyz]₄ [Sb₁₀ I₃₄ ], that can be well understood using quantum chemical investigations. Also using SbI₃ and [H₂ NMe₂ ]₃ [SbI₆ ], a compound featuring a single octahedral [SbI₆ ]^3- unit, as limiting cases, we show that structure-property relationships can be established in group 15 halogenido metalates in a similar way as in metal halide perovskites, thus providing a framework for understanding new and known compounds in this emerging class of materials.

Bi(III) halometallate ionic liquids: Interactions and speciation

Bismuth containing compounds are of particular interest for optical or photo-luminescent applications in sensing, bio-imaging, telecommunications, and opto-electronics and as components in non-toxic extremely dense liquids. Bismuth(III) halometallates form highly colored novel ionic liquid based solvents for which experimental characterization and fundamental understanding are limited. In this work, Bismuth(III) halometallates incorporating chloride, bromide, and iodide have been studied via density functional theory employing B3LYP-D3BJ/aug-cc-pVDZ. Lone anions, and anions in clusters with sufficient 1-ethyl-3-methyl-imidazolium [C₂C₁Im]⁺ counter-cations to balance the charge, have been investigated in the gas- phase, and with polarizable continuum solvation. Evaluation of speciation profiles indicates that dimeric or trimeric anions are prevalent. In contrast to analogous Al systems, anions of higher charge (-2, -3) are present. Speciation profiles are similar, but not identical with respect to the halide. The Bi based anions [Bi_mX_n]^x- in the gas phase and generalized solvation environment produce multiple low energy conformers; moreover, key structural interaction patterns emerge from an analysis of ion-pair and neutral-cluster structures (Bi_mX_n)^x-(C₂C₁Im)_x ⁺ for x = 1, 2, and 3. Cation-anion interactions are weak; with Coulombic and dispersion forces predominating, anion-π structures are favored, while significant hydrogen bonding does not occur. Anion to cation charge transfer is minimal, but mutual polarization is significant, leading to local positive regions in the anion electrostatic potential surface. The key features of experimental x-ray photoelectron, UV-Vis spectra, and Raman spectra are reproduced, validating the computational results and facilitating rationalization of key features.

Using a Porphyrin Diacid Cation to Stabilize a Square-Pyramidal BiX5 (X = Br, Cl/Br) Unit

Main-group halogenido metalates are a diverse class of compounds with an intricate structural chemistry and a wide range of applications. Here, we present an unprecedented anion motif in the structural chemistry of halogenido bismuthates, a square-pyramidal BiX₅ unit. We show how the porphyrin diacid used as our compounds' counterion is templating the formation of this new motif, suggesting that other strong anion receptors may be able to stabilize unique metalate anions in future work.

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).

Efficient Lone-Pair-Driven Luminescence: Structure-Property Relationships in Emissive 5s2 Metal Halides

Low-dimensional metal halides have been the focus of intense investigations in recent years following the success of hybrid lead halide perovskites as optoelectronic materials. In particular, the light emission of low-dimensional halides based on the 5s2 cations Sn2+ and Sb3+ has found utility in a variety of applications complementary to those of the three-dimensional halide perovskites because of its unusual properties such as broadband character and highly temperature-dependent lifetime. These properties derive from the exceptional chemistry of the 5s2 lone pair, but the terminology and explanations given for such emission vary widely, hampering efforts to build a cohesive understanding of these materials that would lead to the development of efficient optoelectronic devices. In this Perspective, we provide a structural overview of these materials with a focus on the dynamics driven by the stereoactivity of the 5s2 lone pair to identify the structural features that enable strong emission. We unite the different theoretical models that have been able to explain the success of these bright 5s2 emission centers into a cohesive framework, which is then applied to the array of compounds recently developed by our group and other researchers, demonstrating its utility and generating a holistic picture of the field from the point of view of a materials chemist. We highlight those state-of-the-art materials and applications that demonstrate the unique capabilities of these versatile emissive centers and identify promising future directions in the field of low-dimensional 5s2 metal halides.

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.

Broad-band luminescence involving fluconazole antifungal drug in a lead-free bismuth iodide perovskite: Combined experimental and computational insights

The synthesis and characterization of a lead-free perovskite-type material, (C₁₃H₁₄N₆F₂O)₂ Bi₂I₁₀ is reported. It exhibits a zero-dimensional (0D) Bi₂I₁₀^4- octahedral unit, surrounded by a flexible tripodal antifungal ligand (H₂Fluconazole)²⁺. The several intermolecular interactions of the independent cation and the bismuth iodide octahedra were tested via the Hirshfeld surface analysis. The detailed interpretation of the vibrational modes was carried out. The band gap (Eg) of 2.10 eV agrees with the theoretical values. Upon photoexcitation, the crystals exhibit a broadband green emission peaked at 534 nm, which originates from electronic transitions within the inorganic cluster [Bi₂I₁₀]^4-. The theoretical calculations were carried out using DFT and TD-DFT methods to appraise the molecular geometry, vibrational spectra, electronic absorption spectra, frontier molecular orbitals (FOMs) and global reactivity descriptors. Calculations reveal that the energy gap (Eg) and other chemical reactivity descriptors are primarily linked to the inorganic anion and the triazolium rings (A and B) of the organic cation reflecting their importance in the activity and the antioxidant ability of the molecule.

The crystal structures of α-Rb7Sb3Br16, α- and β-Tl7Bi3Br16 and their relationship to close packings of spheres

Yellow prismatic crystals of rubidium bromido-antimonate(III) Rb7Sb3Br16 and of two different modifications of thallium bromido-bismuthate(III) Tl7Bi3Br16 were obtained by solvent-free synthesis and by precipitation from acidic aqueous solutions. X-ray diffraction analyses revealed the Tl7Bi3I16-type for α-Tl7Bi3Br16 (orthorhombic, Cmcm, a = 2324.31(8) pm, b = 1346.69(4) pm, c = 3460.0(1) pm; Pearson symbol oC312) and a new structure type for β-Tl7Bi3Br16 (monoclinic, C2/c, a = 2331.87(5) pm, b = 1343.33(3) pm, c = 3546.01(7) pm, β = 102.708(1)°; mC312). The antimonate Rb7Sb3Br16 adopts the Tl7Bi3I16-type, too (orthorhombic, Cmcm, a = 2347.16(3) pm, b = 1357.89(5) pm, c = 3539.47(9) pm; oC312). The crystal structures of α- and β-Tl7Bi3Br16 comprise alternating slabs of isolated [BiBr6]3– octahedra and [Bi2Br10]4– octahedra pairs. Both structure types are hierarchically organized and can be regarded as sphere close packing with the same stacking sequence, if octahedra and octahedra pairs are replaced by spheres of equal size. The structural relationship between the Tl7Bi3I16-type and the hydrate Na7Bi3Br16 · 18H2O, which comprises similar structural features, is discussed.

Isostructural Inorganic–Organic Piperazine-1,4-diium Chlorido- and Bromidoantimonate(III) Monohydrates: Octahedral Distortions and Hydrogen Bonds

Halogenidoantimonate(III) monohydrates of the (C₄H₁₂N₂)[SbX₅]·H₂O (X = Cl, 1 or Br, 2) formula, crystallizing in the same monoclinic space group of P2₁/n, are isostructural, with an isostructurality index close to 99%. The single crystal X-ray diffraction data do not show any indication of phase transition in cooling these crystals from room temperature to 85 K. Both hybrid crystals are built up from [SbX₆]^3– octahedra that are joined together by a common edge forming isolated bioctahedral [Sb₂X₁₀]^4– units, piperazine-1,4-diium (C₄H₁₂N₂)²⁺ cations and water of crystallization molecules. These structural components are joined together by related but somewhat different O/N/C–H···X and N–H···O hydrogen bonded systems. The evolution of structural parameters, notably the secondary Sb–X bonds along with the associated X/Sb–Sb/X–X/Sb angles and O/N/C–H···X hydrogen bonds, as a function of ligand exchange and temperature, along with their influence on the irregularity of [SbX₆]^3– octahedra, was determined. The comparison of packing features and hydrogen bond parameters, additionally supported by the Hirshfeld surface analysis and data retrieved from the Cambridge Structural Database, demonstrates the hierarchy and importance of hydrogen bond interactions that influence the irregularity of single [SbX₆]^3– units.

(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.

Divergent Optical Properties in an Isomorphous Family of Multinary Iodido Pentelates

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 of four new multinary iodido pentelates [PPh₄]₂[ECu₂I₇(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 [EI₆]^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.

Surprising discoveries on the way to an old compound: four transient iodido antimonates

During the synthesis of the literature-known iodido antimonate [Cu(MeCN)4]4[Sb3I11]2 (MeCN = acetonitrile), four transient compounds, [Cu(MeCN)4]4[Sb6I22]·2MeCN (1), [Cu(MeCN)4]4[Sb7I25]·MeCN (2), [Cu(MeCN)4]4[Sb10I34] (3) and [Cu(MeCN)4]4[Sb8I28] (4), were identified. The compounds appeared within hours or days and subsequently re-dissolved in the mother liquor, leading to [Cu(MeCN)4]4[Sb3I11]2 as the final product. Single crystal X-ray analysis showed that all four compounds feature unprecedented anion motifs.

A Novel Family of Polyiodo-Bromoantimonate(III) Complexes: Cation-Driven Self-Assembly of Photoconductive Metal-Polyhalide Frameworks

In the presence of different cations, reactions of [SbBr₆ ]^3- and I₂ result in a new family of diverse supramolecular 1D polyiodide-bromoantimonate networks. The coordination number of Sb, as well as geometry of assembling {I_x }^n- polyhalide units, can vary, resulting in unprecedented structural types. The nature of I⋅⋅⋅Br interactions was studied by DFT calculations; estimated energy values are 1.6-6.9 kcal mol^-1 . Some of the compounds showed strong photoconductivity in thin films, suggesting multiple feasible applications in optoelectronics and solar energy conversion.

Diimidazolium Halobismuthates [Dim]2[Bi2X10] (X = Cl-, Br-, or I-): A New Class of Thermochromic and Photoluminescent Materials

We present a novel family of polyhalide salts of Bi(III) with the general formula [Dim]₂[Bi₂X₁₀], where Dim²⁺ is the diimidazolium cation (C₉H₁₄N₄)²⁺ and X is Cl^-, Br^-, or I^-. Single-phase materials are easily obtained by means of a mild solution chemistry method performed at room temperature. This [Dim]₂[Bi₂X₁₀] family exhibits a crystal structure based on halobismuthate [Bi₂X₁₀]^4- dimers, built by distorted {BiX₆} octahedra interconnected by edge sharing, and sandwiched between two diimidazolium cations. The optical band gaps displayed by these materials (1.9-3.2 eV) allow their classification as semiconductors. Additionally, the three halides display photoluminescence with emission in the visible range. The behavior of [Dim]₂[Bi₂I₁₀] is particularly interesting, as it shows an optical band gap of 1.9 eV, a broad band photoluminescence emission, and a relatively long emission lifetime of 190 ns. Moreover, the iodide and bromide compounds also exhibit a reversible solid state thermochromism, being the first example of a bromobismuthate with this property. The diimidazolium cations play an important structural role by stabilizing the crystal structure and balancing the charges of the [Bi₂X₁₀]^4- dimers. Furthermore, density functional theory calculations suggest that they play a key role in the thermochromic behavior. Therefore, compounds [Dim]₂[Bi₂X₁₀] (X = Cl^-, Br^-, or I^-) represent a very versatile family in which the optical band gap can be tuned by changing the halide or temperature. This makes them promising new materials for different optoelectronic applications, in particular for obtaining new solar absorbers.

Iodoargentate/iodobismuthate-based materials hybridized with lanthanide-containing metalloviologens: thermochromic behaviors and photocurrent responses

New hybrids combined metalloviologens with Ag/Cu iodides exhibit reversible thermochromisms, photocurrent responses, whose mechanisms are disclosed.

Synthesis, structure and optoelectronic properties of hybrid iodobismuthate & iodoantimonate semiconducting materials

The syntheses, structures and optical absorption spectra of five iodobismuthate and nine iodoantimonate hybrid materials are presented.

Crystal Structure and Transport Properties of the Homologous Compounds (PbSe)5(Bi2Se3)3m (m = 2, 3)

We report on a detailed investigation of the crystal structure and transport properties in a broad temperature range (2-723 K) of the homologous compounds (PbSe)₅(Bi₂Se₃)_3m for m = 2, 3. Single-crystal X-ray diffraction data indicate that the m = 2, 3 compounds crystallize in the monoclinic space groups C2/m (No. 12) and P2₁/m (No. 11), respectively. In agreement with diffraction data, high-resolution transmission electron microscopy analyses carried out on single crystals show that the three-dimensional crystal structures are built from alternating Pb-Se and m Bi-Se layers stacked along the a axis in both compounds. Scanning electron microcopy and electron-probe microanalyses reveal deviations from the nominal stoichiometry, suggesting a domain of existence in the pseudo binary phase diagram at 873 K. The complex atomic-scale structures of these compounds lead to very low lattice thermal conductivities κ_L that approach the glassy limit at high temperatures. A comparison of the κ_L values across this series unveiled an unexpected increase with increasing m from m = 1 to m = 3, in contrast to the expectation that increasing the structural complexity should tend to lower the thermal transport. This result points to a decisive role played by the Pb-Se/Bi-Se interfaces in limiting κ_L in this series. Both compounds behave as heavily doped n-type semiconductors with relatively low electrical resistivity and thermopower values. As a result, moderate peak ZT values of 0.25 and 0.20 at 700 K were achieved in the m = 2, 3 compounds, respectively. The inherent poor ability of these structures to conduct heat suggests that these homologous compounds may show interesting thermoelectric properties when properly optimized by extrinsic dopants.

Crystal Structure and Thermoelectric Properties of the 7,7L Lillianite Homologue Pb6Bi2Se9

Pb₆Bi₂Se₉, the selenium analogue of heyrovsyite, crystallizes in the orthorhombic space group Cmcm (#63) with a = 4.257(1) Å, b = 14.105(3) Å, and c = 32.412(7) Å at 300 K. Its crystal structure consists of two NaCl-type layers, A and B, with equal thickness, N₁ = N₂ = 7, where N is the number of edge-sharing [Pb/Bi]Se₆ octahedra along the central diagonal. In the crystal structure, adjacent layers are arranged along the c-axis such that bridging bicapped trigonal prisms, PbSe₈, are located on a pseudomirror plane parallel to (001). Therefore, Pb₆Bi₂Se₉ corresponds to a ^7,7L member of the lillianite homologous series. Electronic transport measurements indicate that the compound is a heavily doped narrow band gap n-type semiconductor, with electrical conductivity and thermopower values of 350 S/cm and -53 μV/K at 300 K. Interestingly, the compound exhibits a moderately low thermal conductivity, ∼1.1 W/mK, in the whole temperature range, owing to its complex crystal structure, which enables strong phonon scattering at the twin boundaries between adjacent NaCl-type layers A and B. The dimensionless figure of merit, ZT, increases with temperature to 0.25 at 673 K.

Orthoamide und Iminiumsalze, XCI. N,N′,N″-Peralkylierte Guanidiniumsalze – Ionische Flüssigkeiten als Hilfsmittel in der Elektronenmikroskopie

Polymeric organic materials, e.g. cellulose fibres or nylon 6 (perlon), as well as inorganic materials, e.g. ceramics, can be coated with liquid or solid guanidinium salts. The coated materials can be inspected by scanning electron microscopy (SEM). The contrast and brightness of the pictures depend on the heaviest atom present in the anions. The best brightness and contrast were obtained with N,N′,N″-peralkylated guanidinium tetraiodidobismutates(III), which were prepared for the first time together with other guanidinium chloridometallates (Sb, Pb, Bi). Biological samples (cell cultures) can also be investigated by SEM with the aid of the guanidinium tetrachloridobismutate 4b after simple sample preparation.

Synthesis of Bi2Te3and (BixSb1−x)2Te3nanoparticles using the novel IL [C4mim]3[Bi3I12]

[C₄mim]₃[Bi₃I₁₂] is a promising Bi-source for the ionothermal synthesis of binary (Bi₂Te₃) and ternary tetradymite-type nanoparticles (Bi_xSb_1−x)₂Te₃(x= 0.25, 0.5, 0.75) in ionic liquid.

Heterogeneous bromination of alkenes using Bi(iii) polybromide complexes as {Br2} source

A new polybromide Bi(iii) complex (PyH)₃{[Bi₂Br₉](Br₂)} was synthesized, characterized by XRD, and used for selective bromination of alkenes.