Iodobismuthates Containing One-Dimensional BiI4(-) Anions as Prospective Light-Harvesting Materials: Synthesis, Crystal and Electronic Structure, and Optical Properties

Syntheses, structures, photoelectric properties and photocatalysis of iodobismuthate hybrids with lanthanide complex cations

New iodobismuthate hybrids with lanthanide complex counter cations, [Ln(DMF)₈][Bi₂I₉] (Ln = La (1), Eu (2)) and [Tb(DMF)₈]₂[Bi₂I₉]₂ (3) (DMF = N,N-dimethylformamide), were prepared using solvated Ln(III) complexes formed in situ as structure-directing agents. The dimeric [Bi₂I₉]^3- anion moieties of compounds 1-3 are aggregated by two slightly twisted BiI₆ octahedra through face-sharing mode. The different crystal structures of 1-3 are due to the different I⋯I and C-H⋯I hydrogen bond interactions. Compounds 1-3 have narrow semiconducting band gaps at 2.23, 1.91 and 1.94 eV, respectively. Under Xe light irradiation, they exhibit steady photocurrent densities that are 1.81, 2.10 and 2.18 times higher than that of pure BiI₃, respectively. Compounds 2 and 3 exhibited higher catalytic activities than 1 in the photodegradation of organic dyes CV and RhB, which are attributed to the stronger photocurrent response derived from the redox cycles of Eu³⁺/Eu²⁺ and Tb⁴⁺/Tb³⁺.

A semiconductive copper iodobismuthate hybrid: structure, optical properties and photocurrent response

Pursuits of new types of Pb-free heterometallic halides adequate for photovoltaic applications are still urgent but challenging. In this study, by using in situ-produced [(Me)₂-(DABCO)]²⁺ (DABCO = 1,4-diazabicyclo[2.2.2]octane; Me = methyl) cations as structure-directing agents, we successfully constructed a non-perovskite copper iodobismuthate hybrid, namely [(Me)₂-(DABCO)]₂Cu₂Bi₂I₁₂ (1), which features discrete [Cu₂Bi₂I₁₂]^4- anionic moieties formed by the building units of [CuI₄] tetrahedra and [BiI₆] octahedra. UV-Vis diffuse reflectance analyses showed that compound 1 possesses semiconductive behaviors with a narrow optical bandgap of 1.80 eV. More importantly, it exhibits excellent photoelectric switching abilities, and its photocurrent density (2.30 μA cm^-2) far exceeds those of some high-performance halide-based counterparts. Different from many heterometallic analogues, noteworthily, it also has dispersive band structure and strong electronic coupling near the Fermi level, resulting in a material with small effective masses that may be responsible for the good photoelectricity. This study may offer new guidance for the design and synthesis of eco-friendly heterometallic halides with unique structures and desirable properties.

Synthesis, Crystal, and Electronic Structure of (HpipeH2)2[Sb2I10](I2), with I2 Molecules Linking Sb2X10 Dimers into a Polymeric Anion: A Strategy for Optimizing a Hybrid Compound's Band Gap

In searching for a tool for optimizing the band gap of a hybrid compound capable of serving as a light-harvesting material in lead-free photovoltaics, we synthesized a new polyiodoantimonate (HpipeH₂)₂[Sb₂I₁₀](I₂) and analyzed its crystal and electronic structure by application of X-ray crystal structure analysis, Raman and diffuse reflectance spectroscopies, and quantum chemical calculations. It was demonstrated that I₂ molecules link Sb₂I₁₀ edge-sharing octahedra into zig-zag chains, whereas the organic cations link inorganic anionic chains into a 3D structure featuring a complex pattern of covalent bonds and non-covalent interactions. Overall, these features provide the background for forming the electronic structure with a narrow band gap of 1.41 eV, therefore being a versatile tool for optimizing the band gap of a potential light-harvesting hybrid compound.

Influence of interaction between organic cation and inorganic unit in bi-based hybrid perovskites for photoelectronic properties

With the increase of the passion on lead-free perovskites, more and more endeavor focused on halobismuthates. Here, we have introduced the p-iodoaniline and p-phenylenediamine into Bi-based hybrid materials, and two photoactive iodobismuthate named p-phenylenediamine iodobismuthate (PDABI) and p-iodoaniline iodobismuthate (PIDBI) were prepared. Their single structures, band gaps, thermostability and other properties were explored. The structure results revealed that they all have 1D BiI₄ ^- anion chains with edge-shared BiI₆ octahedron. The DFT result revealed that PIDBI had an inherent interaction between the I substituent in p-iodoaniline cation and the Bi atom in inorganic BiI₄ ^- anion chains. The photodetector assembled by PDABI and PIDBI revealed that the interaction provided by symmetric p-phenylenediamine has a positive effect on PIDBI's optoelectronic properties compared to the role of asymmetric p-iodoaniline in PDABI.

A new metal complex-templated silver iodobismuthate exhibiting photocurrent response and photocatalytic property

An organic-inorganic hybrid silver iodobismuthate characteristic of the infrequent [Ag₂BiI₆L₂] cluster (L = I or I₃) and with a unique Ag/Bi molar ratio (2/1), namely, [Zn(bipy)₃]₂Ag₂BiI₆(I)_1.355(I₃)_1.645 (bipy = 2,2'-bipyridine; 1), was solvothermally synthesized, and structurally, optically, and theoretically studied. Intriguingly, compound 1 exhibited semiconductor behavior with an optical band gap of 2.33 eV, which endowed it with excellent photoelectric and photocatalytic properties. Electronic structure calculations further revealed that the relative separate conduction band (CB) and valence band (VB) in compound 1 may be responsible for the good optical activity. This study also includes the Hirshfeld surface analyses, thermogravimetric measurements and X-ray photoelectron spectroscopy (XPS) characterization.

Bismuth(III) Iodide Complexes with 1-Ethyl-4-Dimethylaminopyridinium: Structure, Thermal Stability, and Optical Properties

Abstract

Polynuclear bismuth(III) iodide complexes with 1-ethyl-4-dimethylaminopyridinium (1-EtDMAP)4[Bi8I28] (1) and (1-EtDMAP)BiI4 (2) have been obtained by the reactions of bismuth(III) iodide with an organic iodide salt cations in organic solvents and characterized by X-ray diffraction. The optical properties and thermal stability of the obtained compounds have been studied.

Molecular and Supramolecular Structures of Triiodides and Polyiodobismuthates of Phenylenediammonium and Its N,N-dimethyl Derivative

Despite remarkable progress in photoconversion efficiency, the toxicity of lead-based hybrid perovskites remains an important issue hindering their applications in consumer optoelectronic devices, such as solar cells, LED displays, and photodetectors. For that reason, lead-free metal halide complexes have attracted great attention as alternative optoelectronic materials. In this work, we demonstrate that reactions of two aromatic diamines with iodine in hydroiodic acid produced phenylenediammonium (PDA) and N,N-dimethyl-phenylenediammonium (DMPDA) triiodides, PDA(I₃)₂⋅2H₂O and DMPDA(I₃)I, respectively. If the source of bismuth was added, they were converted into previously reported PDA(BiI₄)₂⋅I₂ and new (DMPDA)₂(BiI₆)(I₃)⋅2H₂O, having band gaps of 1.45 and 1.7 eV, respectively, which are in the optimal range for efficient solar light absorbers. All four compounds presented organic–inorganic hybrids, whose supramolecular structures were based on a variety of intermolecular forces, including (N)H⋅⋅⋅I and (N)H⋅⋅⋅O hydrogen bonds as well as I⋅⋅⋅I secondary and weak interactions. Details of their molecular and supramolecular structures are discussed based on single-crystal X-ray diffraction data, thermal analysis, and Raman and optical spectroscopy.

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.

The solvothermal syntheses, crystal structures, and optical properties of four new iodobismuthates containing 1,4-diazabicyclo[2.2.2]octane (DABCO) are described. In the absence of hydriodic acid, DABCO can act as a ligand instead of acting as a countercation.

Synthesis and supramolecular organization of the iodide and triiodides of a polycyclic adamantane-based diammonium cation: the effects of hydrogen bonds and weak I⋯I interactions

Adamantane-like divalent building blocks and iodide or polyiodide anions combine into supramolecular architectures with the help of various noncovalent forces ranging from strong hydrogen bonds to secondary and weak I⋯I interactions.

Crystal structure, spectroscopic measurement, optical properties, thermal studies and biological activities of a new hybrid material containing iodide anions of bismuth(iii)

As part of our interest in halogenobismuthate(iii) organic-inorganic hybrid materials, a novel compound named bis(4,4'-diammoniumdiphenylsulfone) hexadecaiodotetrabismuthate(III) tetrahydrate with the chemical formula (C₁₂H₁₄N₂O₂S)₂[Bi₄I₁₆]·4H₂O, abbreviated as (H₂DDS)[Bi₄I₁₆], has been prepared by a slow evaporation method at room temperature. This compound was characterized by single crystal X-ray diffraction (SCXRD), spectroscopic measurements, thermal study and antimicrobial activity. The examination of the molecular arrangement shows that the crystal packing can be described as made of layers of organic [C₁₂H₁₄N₂O₂S]²⁺ entities and H₂O molecules, between which tetranuclear [Bi₄I₁₆]^4- units, isolated from each other, are inserted. The cohesion among the different molecules is assured by N-H⋯I, N-H⋯O and O-H⋯I hydrogen bonding interactions, forming a three-dimensional network. Room temperature IR, Raman spectroscopy of the title compound were recorded and analyzed. The optical properties were also investigated by both UV-vis and photoluminescence spectroscopy. Moreover, the synthesized compound was also screened for in vitro antimicrobial (Gram-positive and Gram-negative) and antioxidant activities (scavenging effect on DPPH free radicals, reducing power and total antioxidant capacity).

A Potential Checkmate to Lead: Bismuth in Organometal Halide Perovskites, Structure, Properties, and Applications

The remarkable optoelectronic properties and considerable performance of the organo lead-halide perovskites (PVKs) in various optoelectronic applications grasp tremendous scientific attention. However, the existence of the toxic lead in these compounds is threatening human health and remains a major concern in the way of their commercialization. To address this issue, numerous nontoxic alternatives have been reported. Among these alternatives, bismuth-based PVKs have emerged as a promising substitute because of similar optoelectronic properties and extended environmental stability. This work communicates briefly about the possible lead-alternatives and explores bismuth-based perovskites comprehensively, in terms of their structures, optoelectronic properties, and applications. A brief description of lead-toxification is provided and the possible Pb-alternatives from the periodic table are scrutinized. Then, the classification and crystal structures of various Bi-based perovskites are elaborated on. Detailed optoelectronic properties of Bi-based perovskites are also described and their optoelectronic applications are abridged. The overall photovoltaic applications along with device characteristics (i.e., V OC, J SC, fill factor, FF, and power conversion efficiency, PCE), fabrication method, device architecture, and operational stability are also summarized. Finally, a conclusion is drawn where a brief outlook highlights the challenges that hamper the future progress of Bi-based optoelectronic devices and suggestions for future directions are provided.

Assembling Polyiodides and Iodobismuthates Using a Template Effect of a Cyclic Diammonium Cation and Formation of a Low-Gap Hybrid Iodobismuthate with High Thermal Stability

Exploiting a template effect of 1,4-diazacycloheptane (also known as homopiperazine, Hpipe), four new hybrid iodides, (HpipeH₂)₂Bi₂I₁₀·2H₂O, (HpipeH₂)I(I₃), (HpipeH₂)₃I₆·H₂O, and (HpipeH₂)₃(H₃O)I₇, were prepared and their crystal structures were solved using single crystal X-ray diffraction data. All four solid-state crystal structures feature the HpipeH₂²⁺ cation alternating with Bi₂I₁₀^4–, I₃^–, or I^– anions and solvent water or H₃O⁺ cation. HpipeH₂²⁺ assembles anionic and neutral building blocks into polymer structures by forming four strong (N)H···I and (N)H···O hydrogen bonds per cation, with the H···I distances ranging from 2.44 to 2.93 Å and H···O distances of 1.88–1.89 Å. These hydrogen bonds strongly affect the properties of compounds; in particular, in the case of (HpipeH₂)₂Bi₂I₁₀·2H₂O, they ensure narrowing of the band gap down to 1.8 eV and provide high thermal stability up to 240 °C, remarkable for a hydrated molecular solid.

Non-transient thermo-/photochromism of iodobismuthate hybrids directed by solvated metal cations

Two iodobismuthate-based organic-inorganic hybrids, [M(DMSO)₈][Bi₂I₉] (M = La (1), Bi (2)), have been successfully designed and synthesized by using solvated metal cations as structure-directing agents (SDAs). 1 displays transient high-temperature thermochromism, which is similar to that of the characteristic low-temperature thermochromic properties of bulk bismuth iodide and iodobismuthate hybrids. In contrast, 2 exhibits distinguishing non-transient thermochromic properties stimulated by the different temperature ranges of the thermal treatments. More importantly, a comparison of the optical inertness of 1 and 2 also reveals novel photochromic behavior. The completely different thermo-/photo-responsive properties of 1 and 2 are mainly ascribed to the different binding abilities of the central metal cations with DMSO molecules, which cause a distinct transformation of the inorganic moiety and consequent modulation of band gaps.

Additive-assisted synthesis and optoelectronic properties of (CH3NH3)4Bi6I22

A novel iodobismuthate semiconductor (MA)₄Bi₆I₂₂ (measured bandgap of 1.9 eV) was prepared using solution methods in the presence of HgI₂ additive.

Crystal and Band-Gap Engineering of One-Dimensional Antimony/Bismuth-Based Organic-Inorganic Hybrids

Hybrid halide perovskites are emerging semiconducting materials with a diverse set of remarkable optoelectronic properties. Besides the widely studied lead halide perovskites, Pb-free metal halides such as Bi- and Sb-containing hybrid organic-inorganic materials have shown potential as semiconductors and have been deemed candidates for optoelectronic devices. Here, we report a series of 1D Sb/Bi-based organic-inorganic hybrid alloys: [4ApyH]Sb_xBi_1-xI_yBr_4-y, where 4ApyH stands for the 4-aminopyridine cations. These compounds are assembled by edge-sharing octahedral [MX₆] units stabilizing 1D chains with organic cations filled in between. The crystallographic data of eight selected complexes show that [4ApyH]Sb_xBi_1-xI_yBr_4-y has at least five phases (space group) with the difference metal and halogen content: Pbca ([4ApyH]BiI₄), Pca2₁ ([4ApyH]Sb_0.5Bi_0.5I₄), P2₁/c ([4ApyH]SbI₄ (100 K), [4ApyH]BiI₂Br₂, [4ApyH]BiBr₄, and [4ApyH]SbBr₄ (100 K)), I2/a ([4ApyH]Sb_0.5Bi_0.5I₂Br₂and [4ApyH]SbI₂Br₂), and C2/c ([4ApyH]SbI₄ (298 K) and [4ApyH]SbBr₄ (298 K)). Powder X-ray diffraction shows that the phase of the sample changes with a change of the metal and halogen ratios, and the change law accords with Vegard's law. The optical band gaps are heavily affected by the metal and halide contents, ranging from 1.94 eV for [4ApyH]BiI₄ to 2.73 eV for [4ApyH]SbBr₄. When Sb substitutes for Bi to form an alloy, the band gap increases from 1.94 for [4ApyH]BiI₄ to 1.67 eV for [4ApyH]SbI₄, from 2.13 eV for [4ApyH]BiI₂Br₂ to 2.41 eV for [4ApyH]SbI₂Br₂, and from 2.55 eV for [4ApyH]BiBr₄ to 2.73 eV for [4ApyH]SbBr₄. The conductivity of [4ApyH]Sb_xBi_1-xI₄ increased from ∼1.00 × 10^-15 to 2.14 × 10^-8 S cm^-1 with an increase of the Sb content. Solution-deposited thin films of the nine complexes show the same (110) orientation, displaying a parallel growth orientation with respect to the substrate. The devices of [4ApyH]Sb_0.8Bi_0.2I₄ and [4ApyH]SbI₄ demonstrated stable open-circuit photovoltages of 0.55 and 0.44 V, steady-state short-circuit photocurrent densities of 1.52 and 1.81 mA cm^-2, and light-to-electrical energy conversion efficiencies of 0.29% and 0.30%, respectively.

Potential Substitutes for Replacement of Lead in Perovskite Solar Cells: A Review

Lead halide perovskites have displayed the highest solar power conversion efficiencies of 23% but the toxicity issues of these materials need to be addressed. Lead-free perovskites have emerged as viable candidates for potential use as light harvesters to ensure clean and green photovoltaic technology. The substitution of lead by Sn, Ge, Bi, Sb, Cu and other potential candidates have reported efficiencies of up to 9%, but there is still a dire need to enhance their efficiencies and stability within the air. A comprehensive review is given on potential substitutes for lead-free perovskites and their characteristic features like energy bandgaps and optical absorption as well as photovoltaic parameters like open-circuit voltage (V OC), fill factor, short-circuit current density (J  SC), and the device architecture for their efficient use. Lead-free perovskites do possess a suitable bandgap but have low efficiency. The use of additives has a significant effect on their efficiency and stability. The incorporation of cations like diethylammonium, phenylethyl ammonium, phenylethyl ammonium iodide, etc., or mixed cations at different compositions at the A-site is reported with engineered bandgaps having significant efficiency and stability. Recent work on the advancement of lead-free perovskites is also reviewed.

Ferroelectric properties and Raman spectroscopy of the [(C4H9)4N]3Bi2Cl9 compound

The exploration of ferroelectric hybrid materials is highly appealing due to their great technological significance. They have the potential to conserve power and amazing applications in information technology. In line with this, we herein report the development of a [(C₄H₉)₄N]₃Bi₂Cl₉ tetra-alkyl hybrid compound that exhibits ferroelectric properties. The phase purity was confirmed by Rietveld refinement of the X-ray powder diffraction pattern. It crystallizes, at room temperature, in the monoclinic system with the P2₁/n space group. The outcome of temperature dependence of the dielectric constant proved that this compound is ferroelectric below approximately 238 K. The dielectric constants have been fitted using the modified Curie–Weiss law and the estimated γ values are close to 1. This confirms classical ferroelectric behavior. Raman spectroscopy is efficiently utilized to manifest the origin of the ferroelectricity, which is ascribed to the dynamic motion of cations as well as distortion of the anions. Moreover, the analysis of the wavenumbers and the half-width for δ_s(Cl–Bi–Cl) and ω(CH₂) modes, based on the order–disorder model, allowed us to obtain the thermal coefficient and activation energy near the para-ferroelectric phase transition.

The exploration of ferroelectric hybrid materials is highly appealing due to their great technological significance.

Highly efficient and very robust blue-excitable yellow phosphors built on multiple-stranded one-dimensional inorganic-organic hybrid chains

Inorganic-organic hybrid semiconductors are promising candidates for energy-related applications. Here, we have developed a unique class of multiple-stranded one-dimensional (1D) structures as very robust and efficient lighting phosphors. Following a systematic ligand design strategy, these structures are constructed by forming multiple coordination bonds between adjacent copper iodide inorganic building units Cu m I m (m = 2, 4, 6) (e.g. dimer, tetramer and hexamer clusters) and strong-binding bidentate organic ligands with low LUMO energies which give rise to infinite 1D chains of high stability and low bandgaps. The significantly enhanced thermal/photostability of these multiple-stranded chain structures is largely attributed to the multi-dentate nature and enhanced Cu-N bonding, and their excellent blue excitability is a result of using benzotriazole based ligands with low-lying LUMO energies. These facts are confirmed by Density Functional Theory (DFT) calculations. The luminescence mechanism of these compounds is studied by temperature dependent photoluminescence experiments. High internal quantum yields (IQYs) are achieved under blue excitation, marking the highest value reported so far for crystalline inorganic-organic hybrid yellow phosphors. Excellent thermal- and photo-stability, coupled with high luminescence efficiency, make this class of materials promising candidates for use as rare-earth element (REE) free phosphors in energy efficient general lighting devices.

Low-dimensional bismuth(III) iodide hybrid material with high activity for the fast removal of rhodamine B

Organic-inorganic hybrid lead-based perovskite crystal materials have been widely studied due to their excellent optical-electronic properties. However, the toxicity of lead limits their widespread use. Here, a lead-free perovskite-type compound, tetrakis(1,2,3-trimethylimidazolium) di-μ₃-iodido-tetra-μ₂-iodido-decaiodidotetrabismuth(III), (C₆H₁₁N₂)₄[Bi₄I₁₆], has been successfully synthesized by a simple solvothermal method. It exhibits a zero-dimensional (0D) tetrameric structure, including edge-sharing [Bi₄I₁₆]^4- distorted octahedra. The band gap of 2.0 eV is close to that of (NH₄)₃[Bi₂I₉]. Degradation ability measurements were performed to examine the potential application of this material as an alternative for waste-water treatment.

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.

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.