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.

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.

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 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.

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.

Reduction of the host cationic framework charge by isoelectronic substitution: synthesis and structure of Hg7Ag2P8X6 (X = Br, I) and Hg6Ag4P8Br6.

The first compounds, Hg(7)Ag(2)P(8)X(6) (X = Br, I) and Hg(6)Ag(4)P(8)Br(6), featuring the partial isoelectronic substitution of Hg(2+) for Ag(1+) in mercury-pnicogen frameworks have been obtained and structurally characterized. The new compounds are the supramolecular assemblies built of the covalently bonded metal-pnicogen frameworks trapping guests of different complexity. The frameworks feature the perfect ordering of Hg(2+) and Ag(1+) cations and contain P(2)(4)(-) and P(6)(6)(-) phosphorus clusters. The substitution of Hg(2+) with Ag(1+) leads to the reduction in charge of the host cluster-containing cationic matrix and concomitant replacement of the monatomic X(-) guest by a lesser amount of the AgBr(3)(2)(-) anions.