BiI6 Octahedra Research Articles

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.

A bismuth-based (III) hybrid perovskite as a highly air-stable, potential absorber with photoconductive response

Organic-inorganic hybrid perovskites materials (CH3NH3PbI3) are recently great attention in the field of optoelectronic and photovoltaic devices. But, the stability and toxicity issues of the lead have seriously affected its commercial application. Here, we described a novel lead-free hybrid bismuth-based compound, [tert-butylammonium]2 [Bi2I9] (TBI), which adopts a one-dimensional perovskite-like manner containing the corner-sharing BiI6 octahedra structure. TBI displays outstanding light-absorbing properties with a gradual absorption edge at 632 nm, and optical bandgap of ∼1.96 eV which is lower than the bandgap of CH3NH3PbBr3 and its semiconducting properties were steadily confirmed by the positive temperature-dependent conductivity along with the prominent photo-conductive responses in the range of (20 °C) 320–420 K (80 °C). In addition, TBI also shows brilliant phase stability from 1 day to 48 days in the open atmosphere, being much higher than CH3NH3PbI3. This result suggests the potentials of TBI as the excellent absorber for photovoltaic and solar cell applications.

Synthesis, Structure, and Characterization of 4,4'-(Anthracene-9,10-diylbis(ethyne-2,1-diyl))bis(1-methyl-1-pyridinium) Bismuth Iodide (C30H22N2)3Bi4I18, an Air, Water, and Thermally Stable 0D Hybrid Perovskite with High Photoluminescence Efficiency.

4,4'-(Anthracene-9,10-diylbis(ethyne-2,1-diyl))bis(1-methyl-1-pyridinium) bismuth iodide (C30H22N2)3Bi4I18 (AEPyBiI) was obtained as a black powder by a very simple route by mixing an acetone solution of BiI3 and an aqueous solution of C30H22N2I2. This novel perovskite is air and water stable and displays a remarkable thermal stability up to nearly 300 °C. The highly conjugated cation C30H22N2 2+ is hydrolytically stable, being nitrogen atoms quaternarized, and this accounts for the insensitivity of the perovskite toward water and atmospheric oxygen under ambient conditions. The cation in aqueous solution is highly fluorescent under UV irradiation (emitting yellow-orange light). AEPyBiI as well is intensely luminescent, its photoluminescence emission being more than 1 order of magnitude greater than that of high-quality InP epilayers. The crystal structure of AEPyBiI was determined using synchrotron radiation single-crystal X-ray diffraction. AEPyBiI was extensively characterized using a wide range of techniques, such as X-ray powder diffraction, diffuse reflectance UV-vis spectroscopy, Fourier transform infrared (FTIR) and Raman spectroscopies, thermogravimetry-differential thermal analysis (TG-DTA), elemental analysis, electrospray ionization mass spectroscopy (ESI-MS), and photoluminescence spectroscopy. AEPyBiI displays a zero-dimensional (0D) perovskite structure in which the inorganic part is constituted by binuclear units consisting of two face-sharing BiI6 octahedra (Bi2I9 3- units). The C30H22N2 2+ cations are stacked along the a-axis direction in a complex motif. Considering its noteworthy light-emitting properties coupled with an easy synthesis and environmental stability, and its composition that does not contain toxic lead or easily oxidable Sn(II), AEPyBiI is a promising candidate for environmentally friendly light-emitting devices.

Large Conjugated Bis/Triimidazolium Derivatives Directed Iodobismuthates(III): Syntheses, Structures, and Visible-Light-Induced Photocatalytic Properties

Under the direction of large conjugated organic species, a series of novel iodobismuthates(III), [Me3BIP][BiI6] (1, Me3BIP = N,N′,N″-trimethyl-3,5-bis(imidazole-1-yl)pyridine), [Me3BIP][Bi2I9] (2), [Me3TIP][Bi2I9] (3, Me3TIP = N,N′,N″-trimethyl-tris[4-(1H-imidazole-1-yl)-phenyl]amine), and [Me3TIB][Bi2I9] (4, Me3TIB = N,N′,N″-trimethyl-1,3,5-tris(1-imidazolyl)benzene), were synthesized via the solvothermal method. These iodobismuthates display two types of structures: 1 contains a [BiI6]3– monometallic unit, and 2–4 possess binuclear [Bi2I9]3– clusters, which are formed by two BiI6 octahedra via face-sharing. The reactants BIP, TIP, and TIB were in situ transformed into [Me3BIP]3+ in 1 and 2, [Me3TIP]3+ in 3, and [Me3TIB]3+ in 4 through the direct N-methylation reaction. UV–visible spectra analyses imply that all compounds possess potential semiconductor properties with narrow band gaps of 2.14, 2.02, 2.09, and 2.07 eV for 1–4, respectively. Compound 3 has high visible-light-driven photocatalytic degradation activity and good recyclability to organic pollutants. Radical trapping experiments combined with theoretical calculations show that the conjugated organic cations contribute to the narrow band gaps of the semiconductors, which can efficiently restrain the recombination of photogenerated electron–hole pairs, resulting in a good photocatalytic efficiency and stability under visible-light irradiation. It is expected that the work will shed useful insights in exploitation of novel halometallates with narrow energy gaps by employing large conjugated organic templates.

Layered Arrangement of 1D Wavy Chains in the Lead‐Free Hybrid Perovskite (PyrCO2H)2BiI5: Structural Investigations and Properties

AbstractLead free organic‐inorganic hybrid perovskites have attracted increasing attention because of their variety of applications such as photovoltaics or lighting. Here, we reported a new iodobismuthate organic‐inorganic perovskite (PyrCO2H)2BiI5 where PyrCO2H+ is the 4‐carboxy‐1‐methylpyridinium. In the room temperature orthorhombic phase, the one‐dimensional (1D) inorganic framework which consists of cis‐connected corner‐sharing BiI6 octahedra, exhibits a sinusoidal deformation along the chain axis, while a regular chain leading to a sub‐cell is found in the high temperature phase (T>390 K). An original structural feature is the relative position of consecutive 1D chains in planes leading to a layered character of this organic‐inorganic compound. The electrical properties as function frequencies and temperatures have been studied in particular allowing the extraction of Rg and further the calculation of σg=f(T). Interestingly, a change of activation energy is detected at the phase transition temperature (390 K). The higher value of activation energy above 390 K can be attributed to change of the conduction mechanism involving ionic conduction.

Solvent-Mediated 1,ω-Bis(isoquinoline)alkane/Iodobismuthate Hybridized Isomers: Structures and Packing Mode Dependent-Photoluminescence/Thermochromisms

The hybridization of 1,4-bis(isoquinoline)butane (BIQBT2+) cation with iodobismuthate under different solvents produce two isomers α-[(BIQBT)(BiI4)2]n (α-1, in CH3OH/H2O mixed solvent, Triclinic system with P-1 space group) and β-[(BIQBT)(BiI4)2]n (β-1, in CH3OH, Monoclinic system with P21/c space group). The 1-D (BiI4) n n− chains are constructed from the opposite edge-sharing BiI6 octahedra. The (BIQBT)2+ in α-isomer adopts the planar configuration, and that in β-isomer presents the chair-like configuration, as a result, different packing modes (intercalating quasi-3-D mode for α-1 and interlocking 2-D mode for β-1) are observed. Interestingly, from α-1 to β-1, distortion degree of BiI6 octahedron and π–π stacking interaction decrease, but hydrogen bonds number increase. Consequently, due to different packing mode, photoluminescence/thermochromisms can be found in α-1, but those of β-1 are vanished, Theoretical calculation was conducted to disclose the structure/thermochromism correlation.

Novel Viologen/Iodobismuthate Hybrids: Structures, Thermochromisms and Theoretical Calculations

Under the template of methyl viologen (MV2+ = methyl viologen) and ethyl viologen (EV2+ = ethyl viologen), two new viologen/iodobismuthate hybrids, (MV)5(Bi2I10)(Bi2I9)2 (1) and (EV)3(Bi4I18) (2) have been structurally determined. The highly interesting feature of 1 lies in its combination of two kinds of dimeric iodobismuthate clusters, i.e. (Bi2I10)4− and (Bi2I9)3− in one lattice induced by MV2+, which are constructed from edge- and face-sharing BiI6 octahedra respectively. But the (Bi4I18)6− tetramer in 2 is based on edge- and vertex-sharing BiI6 octahedra. C–H···I hydrogen bonds contribute to the formation of quasi-3-D networks. The smaller gap of 1 might be led by more versatile C–H···I hydrogen bond interactions due to the presence of mixed type iodobismuthate clusters. Two hybrids display reversible thermochromism behaviors. Theoretical calculation suggests that the terminal iodine is dominated in electron transfer of thermochromisms, rather than bridged iodine.

The Optical Band-Gap Evolution in Perovskite-Like Hybrid Iodobismuthates Effected by Nuclearity and Dimension: An Experimental and DFT Calculation Study

Three new perovskite-like hybrid iodobismuthates with two quaternary ammonium cations, namely (BnNEt3)3(Bi2I9) (1) (BnNEt3)4(Bi4I16) (2) and (n-Bu4N)2n(Bi4I14)n (3) (Bn = benzyl, n-Bu = n-butyl), have been synthesized by reacting BiI3 with the quaternary ammonium iodide in molar ratio 2:3 (1), 1:1(2), and 2:1 (3), respectively. All hybrids were characterized by elemental analysis, X-ray diffraction and UV–Vis spectroscopic analysis. Single-crystal X-ray diffraction revealed that hybrids 1 and 2 are di-nuclear and tetra-nuclear cluster structures respectively, while 3 is a polymeric chain structure based on a (Bi4I14) tetra-nuclear cluster unit. Their optical band-gaps have been determined as 2.19 eV(1), 2.16 eV(2), 2.02 eV(3), respectively. The optical band gaps exhibit a structure-related decrease from 1 to 3, in agreement with their color changes and the density functional theory (DFT) calculation results. The DFT calculations also reveal that there is a inversely proportional relationship between the optical Eg and the aggregation degree of the BiI6 octahedra in the hybrid iodobismuthate clusters.

A bismuth triiodide monosheet on Bi2Se3(0001)

A stable BiI3 monosheet has been grown for the first time on the (0001) surface of the topological insulator Bi2Se3 as confirmed by scanning tunnelling microscopy, surface X-ray diffraction, and X-ray photoemision spectroscopy. BiI3 is deposited by molecular beam epitaxy from the crystalline BiTeI precursor that undergoes decomposition sublimation. The key fragment of the bulk BiI3 structure, {{rm{a}}}_{infty }^{2}[I—Bi—I] layer of edge-sharing BiI6 octahedra, is preserved in the ultra-thin film limit, but exhibits large atomic relaxations. The stacking sequence of the trilayers and alternations of the Bi—I distances in the monosheet are the same as in the bulk BiI3 structure. Momentum resolved photoemission spectroscopy indicates a direct band gap of 1.2 eV. The Dirac surface state is completely destroyed and a new flat band appears in the band gap of the BiI3 film that could be interpreted as an interface state.

From Isolated Anions to Polymer Structures through Linking with I2: Synthesis, Structure, and Properties of Two Complex Bismuth(III) Iodine Iodides.

We report the synthesis, crystal structures, and optical properties of two new compounds, K18Bi8I42(I2)0.5·14H2O (1) and (NH4)7Bi3I16(I2)0.5·4.5H2O (2), as well as the electronic structure of the latter. They crystallize in tetragonal space group P4/ mmm with the unit cell parameters a = 12.974(1) and c = 20.821(3) Å for 1 and a = 13.061(3) and c = 15.162(7) Å for 2. Though 1 and 2 are not isomorphous, their crystal structures display the same structural organization; namely, the BiI6 octahedra are linked by I2 units to form disordered layers in 1 and perfectly ordered chains in 2. The I-I bond distances in the thus formed I-I-I-I linear links are not uniform; the central bond is only slightly longer than in a standalone I2 molecule, whereas the peripheral bonds are significantly shorter than longer bonds typical for various polyiodides, which is confirmed by Raman spectroscopy. The analysis of the electronic structure shows that the atoms forming the I-I-I-I subunits transfer electron density from their occupied 5p orbitals onto their vacant states as well as onto 6s orbitals of bismuth atoms that center the BiI6 octahedra. This leads to low direct band gaps that were found to be 1.57 and 1.27 eV for 1 and 2, respectively, by optical absorption spectroscopy. Luminescent radiative relaxation was observed in the near-IR region with emission maxima of 1.39 and 1.24 eV for 1 and 2, respectively, in good agreement with the band structure, despite the strong quenching propensity of I2 moieties.

Ternary Iodido Bismuthates and the Special Role of Copper.

Two new, isostructural members of the title material class, [PPh4]4[Cu2Bi2I12] (1) and [PPh4]4[Ag2Bi2I12] (2), have been prepared via a facile solution route. The crystal structure of both compounds features a tetranuclear [M2Bi2I12]4- (M = Cu, Ag) anion that displays an unprecedented face-sharing mode of connection between BiI6 octahedra and MI4 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.

(CH3 )3 NH]3 Bi2 I9 : A Polar Lead-Free Hybrid Perovskite-Like Material as a Potential Semiconducting Absorber.

Perovskite hybrids of lead organometal halides, most notably CH3 NH3 PbI3 , have shown extremely promising applications in the field of optoelectronics, because of their remarkable semiconducting and light-absorbing properties. However, two key issues-the toxicity of lead and the poor ambient instabilities-have restrained their further commercialization. Herein, we have designed a new stable polar lead-free hybrid material by utilizing the strategy of cation substitution, [(CH3 )3 N]3 Bi2 I9 (1), which adopts the 0D inorganic perovskite-like architecture by face-sharing BiI6 octahedra. It is interesting that 1 displays excellent absorbing properties with a narrow optical band gap of ≈2.0 eV, and positive temperature-dependent conductivity confirms its semiconducting behaviors. In addition, 1 has good phase stability against decomposition under ambient conditions, much superior to that of CH3 NH3 PbI3 . This work suggests the potential of 1 as a lead-free semiconducting absorber with high phase stability for photoelectric applications.

Temperature dependence of excitonic emission in [(CH3)2NH2]3[BiI6] organic–inorganic natural self assembled bimodal quantum dots

This paper reports on the optical properties of organic – inorganic natural self assembled bimodal quantum dots (dimetylammonium) hexa-iodobismuthate [(CH3)2NH2]3[BiI6]. The crystal structure consists of isolated BiI6 octahedra, as inorganic ions, surrounded by dimethylamine cations. At room temperature, we investigate the optical properties by: UV/Vis absorption, ellipsometry, diffuse reflectance and photoluminescence. A broad Gaussian-shape luminescence band with a large stokes shift is observed in the red spectral range at 2.15 eV, due to radiative recombination of confined excitons in BiI quantum dots, suggesting that excitons are self trapped. The temperature-dependence of the PL emission is investigated. The observed S-shaped emission behavior is explained by thermal escape occurring at lower temperatures for high-energy dots and carriers being recaptured by dots emitting on the low-energy side of the distribution. A rate equation model, showing agreement with the experimental results, is used to investigate the thermal redistribution of the charge carriers. Exciton binding energies of 149.125 and 295.086 meV were determined from the modified Arrhenius analysis.

Band Gap Insensitivity to Large Chemical Pressures in Ternary Bismuth Iodides for Photovoltaic Applications

Ternary bismuth iodides (A3Bi2I9, where A is a monovalent cation) have been recently suggested as less toxic alternatives to lead halide perovskites for photovoltaic applications. Using density functional theory based calculations, we predict that the band gap in these compounds is insensitive to chemical pressure applied by changing the size of A-site cations, which is confirmed experimentally. We further show that the band gap in A3Bi2I9 compounds increases (or decreases) by stretching (or compressing) Bi2I9 bioctahedra, and the observed band gap insensitivity is a direct result of the counteractive interplay of three factors: the size of the A-site cations, the presence of H-bonds with organic A-site cations, and spin–orbit coupling (SOC) effects. Our study demonstrates that the layered structure of A3Bi2I9 compounds intrinsically limits any significant modification of their band gap and highlights the need for three-dimensional connectivity of BiI6 octahedra in order to achieve high efficiency Bi-base...

Band gap and structure of single crystal BiI3: Resolving discrepancies in literature

Bismuth tri-iodide (BiI3) is an intermediate band gap semiconductor with potential for room temperature gamma-ray detection applications. Remarkably, very different band gap characteristics and values of BiI3 have been reported in literature, which may be attributed to its complicated layered structure with strongly bound BiI6 octahedra held together by weak van der Waals interactions. Here, to resolve this discrepancy, the band gap of BiI3 was characterized through optical and computational methods and differences among previously reported values are discussed. Unpolarized transmittance and reflectance spectra in the visible to near ultraviolet (UV-Vis) range at room temperature yielded an indirect band gap of 1.67 ± 0.09 eV, while spectroscopic ellipsometry detected a direct band gap at 1.96 ± 0.05 eV and higher energy critical point features. The discrepancy between the UV-Vis and ellipsometry results originates from the low optical absorption coefficients (α ∼ 102 cm−1) of BiI3 that renders reflection-based ellipsometry insensitive to the indirect gap for this material. Further, electronic-structure calculations of the band structure by density functional theory methods are also consistent with the presence of an indirect band gap of 1.55 eV in BiI3. Based on this, an indirect band gap with a value of 1.67 ± 0.09 eV is considered to best represent the band gap structure and value for single crystal BiI3.

Iodine‐Induced Solvothermal Formation of Viologen Iodobismuthates

AbstractReactions of BiI3, KI, 4,4′‐bipyridine (4,4′‐bipy) and alcohols (methanol, benzyl alcohol, 2‐propanol or propanol) in the presence of I2 and a small amount of water afforded four iodobismuthate complexes of N,N′‐dialkyl‐4,4′‐bipyridinium (viologen, V2+), [MV][BiI5] (1, MV2+ = N,N′‐dimethyl‐4,4′‐bipyridinium), [BzV]2[Bi2I8(μ‐I)2] (2, BzV2+ = N,N′‐dibenzyl‐4,4′‐bipyridinium), [iPV]2[Bi4I10(μ‐I)4(μ3‐I)2] (3, iPV2+ = N,N′‐diisopropyl‐4,4′‐bipyridinium) and [PV]2[Bi4I8(μ‐I)8] (4, PV2+ = N,N′‐dipropyl‐4,4′‐bipyridinium) under solvothermal conditions. The V2+ dications were formed from iodine‐induced C–O bond cleavage of alcohols followed by alkylation of 4,4′‐bipy. The Bi centre of the [BiI5]2– anion of 1 adopts a square‐pyramidal coordination geometry, whereas the [Bi2I10]4– anion of 2 consists of a dimeric structure comprising two edge‐sharing BiI6 octahedra. The tetranuclear [Bi4I16]4– anion of 3 has an incomplete double cubane structure in which two incomplete [Bi3(μ‐I)2(μ3‐I)2] cubane‐like fragments are fused by sharing two Bi and two μ3‐I atoms, whereas that of 4 contains a bent Bi4 chain in which the [Bi2I10]4– anion of 2 is fused with two BiI6 units through six shared μ‐I atoms. The optical, electrical conductivity and dielectric properties of 1–4 were also investigated.

α- to β-(dmes)BiI5 (dmes = Dimethyl(2-ethylammonium)sulfonium Dication): Umbrella Reversal of Sulfonium in the Solid State and Short I···I Interchain Contacts—Crystal Structures, Optical Properties, and Theoretical Investigations of 1D Iodobismuthates

Syntheses, X-ray structural characterization, optical properties, and electronic structures of 1D metal(III) iodide hybrids, namely, alpha-((CH(3))(2)S(CH(2))(2)NH(3))BiI(5) (1a), beta-((CH(3))(2)S(CH(2))(2)NH(3))BiI(5) (1b), ((CH(3))(2)S(CH(2))(2)NH(3))SbI(5) (2), and (HO(2)C(C(6)H(4))CH(2)NH(3))BiI(4) (3), are reported. According to the results of single-crystal X-ray diffraction analyses, the 1D inorganic chains are constructed by corner-shared M(III)I(6) octahedra in 1a, 1b, and 2 and by edge-shared ones in 3. In polymorphs 1a, 1b, and 2, the polymeric BiI(5)(2-) anionic chains are charge-balanced by the dimethyl(2-ethylammonium)sulfonium (dmes) dications. Complex 1a crystallizes in the polar space group of P2(1)cn. A spectacular umbrella reversal of half sulfonium parts together with the conformational change of half polymeric anions in the crystal structure of 1a occurs at moderate temperature (73 degrees C), leading to the beta-phase 1b, through a reversible single-crystal-to-single-crystal process. Complex 1b, as well as the isotype structure of 2, crystallize in the nonpolar acentric space group of P2(1)2(1)2(1). Because of their acentric structural characteristic, second harmonic generation (SHG) optical properties are observed in the polycrystalline powder samples of 1a, 1b, and 2. It is notable that the SHG signal of 1a is much stronger than that of 1b and 2 owing to the polarity of 1a. Remarkably, the peculiar dissymmetrical dication of dmes is able to modify the bonding features of the inorganic frameworks through shortening I...I distances between adjacent chains (d(I...I) < 4A). The structure of 3, which crystallizes in the triclinic space group P1, features a polymeric anionic chain constructed from edge-shared BiI(6) octahedra. The charge is balanced by the pairs of trans-4-(ammoniummethyl)-cyclohexane-carboxylic acid, which are linked together via the H bonding between the carboxylic groups to form a pseudodication. The results of DFT calculations based on the structures of 1a and 3 indicate that the narrower band gap in 1 appears to be associated on the one hand with a sigma* I-p/Bi-s interaction that moves the Fermi level to higher energy and on the other hand with the interchain I...I contacts.

Structure and Optical Properties of Several Organic−Inorganic Hybrids Containing Corner-Sharing Chains of Bismuth Iodide Octahedra

Two organic-inorganic bismuth iodides of the form (H3N-R-NH3)BiI5 are reported, each containing long and relatively flexible organic groups, R. The norganic framework in each case consists of distorted BiI6 octahedra sharing cis vertexes to form zigzag chains. Crystals of (H3NC18H24S2NH3)BiI5 were grown from a slowly cooled ethylene glycol/2-butanol solution containing bismuth(III) iodide and AETH.2HI, where AETH = 1,6-bis[5'-(2' '-aminoethyl)-2'-thienyl]hexane. The new compound, (H2AETH)BiI5, adopts an orthorhombic (Aba2) cell with the lattice parameters a = 20.427(3) A, b = 35.078(5) A, c = 8.559(1) A, and Z = 8. The structure consists of corrugated layers of BiI5(2-) chains, with Bi-I bond lengths ranging from 2.942(3) to 3.233(3) A, separated by layers of the organic (H2AETH)(2+) cations. Crystals of the analogous (H3NC12H24NH3)BiI5 compound were also prepared from a concentrated aqueous hydriodic acid solution containing bismuth(III) iodide and the 1,12-dodecanediamine (DDDA) salt, DDDA.2HI. (H2DDDA)BiI5 crystallizes in an orthorhombic (Ibam) cell with a = 17.226(2) A, b = 34.277(4) A, c = 8.654(1) A, and Z = 8. The Bi-I bonds range in length from 2.929(1) to 3.271(1) A. While the inorganic chain structure is nearly identical for the two title compounds, as well as for the previously reported (H3NC6H12NH3)BiI5 [i.e., (H2DAH)BiI5] structure, the packing of the chains is strongly influenced by the choice of organic cation. Optical absorption spectra for thermally ablated thin films of the three organic-inorganic hybrids containing BiI5(2-) chains are reported as a function of temperature (25-290 K). The dominant long-wavelength feature in each case is attributed to an exciton band, which is apparent at room temperature and, despite the similar inorganic chain structure, varies in position from 491 to 541 nm (at 25 K).

The phases of Cs3Bi2I9 between RT and 190 K

Abstract The structure of Cs3Bi2I9 has been refined to R = 0.0165 on the basis of X-ray diffraction measurements at T = 290 K (STOE IPDS diffractometer; MoKα -radiation; 296 nonequivalent reflection with I &gt; 2σ(I)). The absorption correction was accounted for by the Gaussian method. The parameters of the hexagonal unit cell are: a = 8.409(1) Å and c = 21.243(5) Å; space group P63/mmc. The structure consists of identical perovskite-like layer fragments described by the general formula A3B2X9 (A = Cs, B = Bi, X = I) with ordered vacancies in the B-sublattice. These fragments alternate along the c-axis and are related by mirror planes which contains the shared faces of the BiI6 octahedra. The analysis of the intensities in the temperature range 288 K to 190 K indicates a reversible phase transition into a monoclinic phase at T = 218 K which is accompanied by twinning. No satellite or superstructure reflections were observed with the current resolution of the diffractometer. The X-ray results are compared wih the studies of the temperature dependence of the linear expansion coefficients, optical characteristics, and the nuclear quadrupole spectra of Cs3Bi2I9.