Motivated by the task to replace toxic lead halide perovskites with lead-free environmentally benign light-harvesting materials for photovoltaics, we have synthesized two new hybrid bromometallates, (AH2)4[Sb2Br10(SbBr6)2(Br)2] (1) and (AH2)2[(BiBr6)(SbBr6)]·2H2O (2), where A = 1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane. Their crystal structures show combinations of Sb3+/Sb5+ (1) or Bi3+/Sb5+ (2) centers each surrounded by six Br- anions forming distorted (Sb3+ or Bi3+) or almost regular (Sb5+) octahedra. These octahedra are arranged in the crystal structure in a perfectly ordered way owing to weak Br⋯Br interactions within the inorganic anionic part and to hydrogen bonds linking inorganic anions and organic cations. The electronic structures of both compounds are alike in that they have M3+/Br- states (M = Sb or Bi) dominating the top of the valence band and acceptor in-gap states formed by the Sb5+/Br- interactions. Such an electronic structure leads to the reduced band gap of 1.27 (1) and 1.58 eV (2), favorable for creating light-harvesting materials for photovoltaics. We support our data by powder and single-crystal X-ray diffraction study, 121Sb Mossbauer spectroscopy, and optical spectroscopy. We infer that tailoring the band gap is a very important step on the way to lead-free light-harvesting materials for photovoltaic applications.

Low-dimensional metal halides emerge as materials for optoelectronics beyond perovskite photovoltaic applications. In a search for physical grounds of optical halometallate properties differences, we have investigated two homologous dications of cyclic aliphatic amines that are homopiperazine (Hpipe, C5H12N2, 1,4-diazocycloheptan) and piperazine (Pipe, C4H10N2, 1,4-diazocyclohexan) as structure-directing agents. Mixing of solutions of respective cations and PbI2 in concentrated hydroiodic acid results in obtaining new compound (HpipeH2){PbI5} (I)& sdot;H2O (1) and (PipeH2){PbI5}(I)& sdot;H2O (2), the latter being described in the literature. 1 and 2 demonstrate analogous yet non-isomorphous crystal structures, they share an identical anionic substructure, composed by a zigzag chain-like cis-{PbI5}3- 1D-anion and an isolated I- ion, as well as the same packing of all structural fragments. This rare situation among low-dimensional hybrid metal halide structures provides a unique platform for disentangling the effects of closely related cations on the supramolecular organization, more importantly, on the geometry of the halometallate anion without packing nuances, and, consequently, on optical properties, especially luminescence. A minor distinction in the cation's size and topology leads to dissimilar hydrogen bond systems and, most critically, distortion degrees of the iodoplumbate anion. Both compounds exhibit dual-band photoluminescence consisting of violet free exciton (FE) and yellow/orange (1/2) self-trapped exciton (STE) emission. The greater distortion of halometallate anion in 1 results in a larger Huang-Rhys factor, which governs the characteristics of the STE band and influences the thermal quenching efficiency. Vibrational spectra and thermal stability are also analyzed and correlated with structural features in this paper.

A new tricationic organic supramolecular tecton has been designed and synthesized. Contrary to known mono- and dicationic species, this new molecule, being a "three-way connector", allows assembling infinite supramolecular sheets and nets upon interaction with appropriate inorganic counterpart complex anions. In this work, triprotonated 6-amino-5,7-dimethyl-1,3-diazaadamantane, comprising two secondary and one primary nitrogen atoms, is used as a trication to form hybrid compounds with iodometallate anions by forming five hydrogen bonds at a time. It is shown that the bulky cation works simultaneously as a spacer and a connector, such that the positions of inorganic [MI6]3- anions (M = Sb or Bi) in the crystal structures are defined by five hydrogen bonds and are well-separated from each other. The latter is considered as a prerequisite for the hybrid compounds to exhibit optical properties originating from the undisturbed electronic structure of individual inorganic anions.

In pursuit of identifying less toxic hybrid compounds suitable for optoelectronic applications, we synthesized a novel homopiperazinium bromoantimonate(iii), (C5H14N2)3{Sb2Br9}2. It readily crystallized from an aqueous hydrobromic acid solution and was found to be stable both in air and upon heating up to 175 degrees C. The crystal structure of the new bromoantimonate(iii) consisted of {Sb2Br9}3- zigzag chains, which were composed of strongly trigonally distorted SbBr63- octahedral anions and C5H14N22+ dications. Weak interactions, including (N)H & ctdot;Br hydrogen bonds and Br & ctdot;Br van der Waals contacts, facilitated the assembly of the structural moieties into a three-dimensional (3D) supramolecular framework. The photoluminescence (PL) spectrum of (C5H14N2)3{Sb2Br9}2 displayed two broad bands in visible and near-infrared regions, which were scarcely detectable at room temperature but gained intensity upon cooling. Red emission at 645 nm, typically observed in zero-dimensional halometallates, was attributed to antimony 5s2 lone-pair-driven luminescence that corresponded to the emission from the self-trapped exciton (STE) state. The title compound also exhibited an atypical PL band at 880 nm, which has been discussed along with the optical properties and Raman spectrum of (C5H14N2)3{Sb2Br9}2.

Two new hybrid iodoantimonates( iii ), (3-C 5 H 12 NO) 4 [Sb 4 I 16 ] · 2 H 2 O ( 1 , 3-C 5 H 12 NO + is 3-hydroxypiperidinium) and (4-C 5 H 12 NO) 4 [Sb 4 I 16 ] · 3 H 2 O ( 2 , 4-C 5 H 12 NO + is 4- hydroxypiperidinium), were synthesized. Their crystal structures were established. The anionic substructures of the new compounds are composed of the same tetranuclear complex anions [Sb 4 I 16 ] 4− . The differences in the structure of 3-hydroxypiperidine and 4-hydroxypiperidine are responsible for the differences in the supramolecular organization of the cationic substructures and in the packing of the structural units. The comparative analysis of hydrogen bonding systems in the structures of compounds 1 and 2 was carried out. The band gap width for compound 1 was estimated at 2.38 eV according to the direct band gap model and at 2.28 eV in terms of the indirect band gap model.

Crystal and electronic structures of a newly synthesized thiazolium pentaiodide, C 3 H 4 NS(I 5 ), were examined in detail. The title pentaiodide crystallizes in the monoclinic space group P 2 1 / m with the unit cell volume of 1289.27(6) Å 3 . Its crystal structure features branched pentaiodide chains composed of alternating I 3 − and I 2 building units, whereas the chains are further linked into a 3D array by thiazolium cations with the help of (N)H⋅⋅⋅I and S⋅⋅⋅I bonds. The electronic structure and bonding assessed by DFT calculations show that covalent interactions within the I 2 and I 3 − units are supplemented by non-covalent (N)H⋅⋅⋅I and S⋅⋅⋅I interactions, which were revealed by the electron localization function and reduced density gradient analyses.

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.

New organic-inorganic hybrid halometallates of the general formula (HpipeH 2 )-[M 2 X 10 ] · 2H 2 O, where M = Sb, Bi; X = Br, I; Hpipe is homopiperazine (C 5 N 2 H 12 ), were synthesized. The crystal structures of three new compounds, α-(HpipeH 2 ) 2 [Sb 2 I 10 ] · 2H 2 O (1) , β-(HpipeH 2 ) 2 [Sb 2 I 10 )]-2H 2 O (2) , and (HpipeH 2 ) 2 [Bi 2 Br 10 ] · 2H 2 O (3) , were determined and analyzed in comparison with the previously synthesized analog (HpipeH 2 ) 2 [Bi 2 I 10 ] · 2H 2 O (4). All four compounds have similar crystal structures, in which inorganic dioctahedral [M 2 X 10 ] 4− anions alternate with organic (HpipeH 2 ) 2+ cations and water molecules to form 3D systems based on (N)H⋯X, (N)H⋯O, and (O)H⋯X hydrogen bonds. In all structures, the (HpipeH 2 ) 2+ cation serves the same template function, forming three (N)H⋯X hydrogen bonds with halogen atoms of the inorganic anion and one (N)H⋯O bond with a water molecule. In going from Sb to Bi and from I to Br, the band gap width increases and reaches 2.89 eV for compound 3 .

The amantadinium iodoacetatobismuthate(III) [C10H15NH3·(CH3)2CO]2[BiI3.67(CH3COO)1.33] is a new hybrid halometallate with iodide ions partially replaced by oxygen-containing acetates to form stronger interaction between the anionic and cationic substructures. The title compound as well-shaped orange-red crystals was synthesized by a facile reaction in acetone solution in the presence of glacial acetic acid. The crystal structure of the compound consists of the infinite anionic chains [BiI3.67(CH3COO)1.33]2– and the countercations [C10H15NH3·(CH3)2CO]+; according to the optical absorption data, the test compound is a semiconductor with a band gap of 2.06 eV.

3-Hydroxypiperidinium pentaiodide was synthesized by a facile reaction in concentrated aqueous HI. Its crystal structure comprises 3-hydroxypiperidinium cations and pentaiodide anions, the latter having geometry of cis-shaped chains composed of I-2 and I-3(-) building units. The analysis of interatomic distances, Raman spectroscopy data, and results of DFT calculations, including non-covalent interaction analysis, showed that the title compound exhibits a complex pattern of covalent and non-covalent interactions. Those include I-I covalent bonds and I...I halogen bonds within the I-5(-) anion as well as (N)H...I and (O)H...I hydrogen bonds and even weaker (C)H...I van-der-Waals interactions between the cations and anions.

The reaction of homopiperazine, C5N2H12, with BiBr3 in strong hydrobromic acid affords a new organic-inorganic hybrid (C5N2H14)2[BiBr6]Br·H2O. It crystallizes in the orthorhombic space group, Pbca, with unit cell dimensions of a = 15.0775 (2), b = 15.7569 (2), and c = 20.7881 (4) Å, and eight formula units per unit cell. The crystal structure features slightly distorted octahedral BiBr63− and monoatomic Br− anions in the inorganic substructure and C5N2H142+ dications and adjacent water molecules in the organic substructure. Various weak interactions that include (N)H···Br, (N)H···O, and (O)H···Br hydrogen bonds ensure the assembling of the structural moieties into a 3D supramolecular structure. (C5N2H14)2[BiBr6]Br·H2O shows two emission bands in the photoluminescence spectrum, a rather narrow deep-blue PL at 432 nm, and a broadband red PL centered at 650 nm. Their nature and relations to the crystal structure are discussed in this paper.

A new organic-inorganic hybrid [{p-(CH3)2NH—C6H4—NH3}2Cl][BiI6] was synthesized and its crystal structure was established. The hybrid consists of an inorganic anion [BiI6]3− and an organic cation [{p-(CH3)2NH-C6H4-NH3}2Cl]3+. The [BiI6]3− anions are linked via non-covalent I...I interactions between axial atoms of neighboring anions to form chains running along the c axis of the tetragonal unit cell. In the cationic part, the Cl− anion is involved in four (N)H…Cl hydrogen bonds with hydrogen atoms of the p-(CH3)2NH—C6H4—NH32+ cation, forming a two-dimensional substructure. Alternating covalent and I...I halogen bonds in the anionic substructure and cation—anion hydrogen bonds provide the formation of a three-dimensional supramolecular structure with a band gap of 1.93 eV.

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.

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.

Hexamethylenetetramine (HMT) was used as a strong base for the preparation of new hybride iodobismuthates, (HMTH)(2)BiI5 center dot(CH3)(2)C=O (1) and (HMTH)(2)BiI5 (2). They crystallize in the orthorhombic system, space group Cmcm, a = 14.4345(3), b = 20.2851(6), c = 10.1637(2) angstrom for 1 and space group Pnma, a = 12.7739(18), b = 10.2589(18), c = 19.264(4) angstrom for 2. In both crystal structures, [BiI6] octahedra share cis-vertices to form (BiI5)(2-) zigzag chains that run along the c-axis in 1 and b-axis in 2 leaving the space filled with organic moieties. 1 loses acetone upon heating transforming into 2; in turn, soaking 2 in acetone yields 1. These transformations do not affect the conformation of the (BiI5)(2-) chains but impact greatly hydrogen bonds that glue together the inorganic anionic chains and organic cations. Rearrangement of hydrogen bonds leads to the change in dimensionality of weak interaction patterns from 1D in 1 to 3D in 2. Electronic structures and spectral and optical properties of these two compounds are also discussed.

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 Bi2I104–, 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.

Crystal and electronic structure of silver-containing metal-inorganic frameworks [Ag3S](NO3) and [Ag4Te](SO4) have been examined. For [Ag3S](NO3), the crystal structure has been re-determined from X-ray single crystal diffraction data and refined to R=2.7% in order to determine the exact position of the nitrate anion. It is shown that the main structural feature of [Ag3S](NO3) and [Ag4Te](SO4) is the framework based on the combination of silver-chalcogen and silver-silver interactions, with guest oxoanions filling the cavities. Effectively, ionic interactions between guest anions and the framework differ significantly from the interactions within frameworks themselves, where the bonding analysis shows the tendency for more covalent bonding and indicates that the bonding patterns are consistent with what is regarded as metallophilic interactions.

Glycinium triiodide was synthesized and its crystal structure was determined. The crystal structure consists of alternating asymmetric triiodide anions characterized by Raman spectroscopy and glycinium cations. The cations and anions form dimers (GlyH) 2 (I 3 ) 2 via (N)H···O, (N)H···I, and (O)H···I hydrogen bonds. The dimers are further linked into chains by secondary I···I interactions between adjacent triiodide anions. The supramolecular structure of glycinium triiodide is discussed in comparison with polyiodides of various cations.