Halobismuthates with bis(pyridinium)alkane cations: Correlations in crystal structures and optical properties

Unusual isostructural Br/I substitution effect on the crystal structure and optical properties of hybrid halobismuthates

The gradual change of the optical properties of solid solutions by variation of the halogen composition is shown.

Ferroelectricity in Ethylammonium Bismuth-Based Organic-Inorganic Hybrid: (C2H5NH3)2[BiBr5]

The (C₂H₅NH₃)₂[BiBr₅] (EBB) crystals adopt the one-dimensional (1D) polymeric anionic form [BiBr₅]_∞^2-, which is preferred by halobismuthates(III) exhibiting polar properties and realized in R₂MX₅ stoichiometry. Differential scanning calorimetry and dilatometric measurements reveal reversible structural phase transitions: at 160 K (phase I → phase II) and 120 K (phase II → phase III). The resolved crystal structures of EBB show the centrosymmetric space group in phase I (Aeam), polar (Pca2₁) in phase II, and polar (Aea2) in phase III. The presence of dielectric hysteresis loops in phases II and III evidence ferroelectric properties. The dielectric response [ε*(ω,T)] of EBB close to 160 K is characteristic of ferroelectrics with a critical slowing down process. The molecular mechanism of a paraelectric-ferroelectric phase transition at 160 K is explained as "order-disorder" (assigned to the dynamics of the ethylammonium cations) and dominating "displacive" (related to strong distortion of the 1D anionic network). The optical band gap obtained from UV-vis measurements is about 2.6 eV. The conduction band minimum is formed by the hybridized Bi 6p and Br 4p states. An analysis of the CSD results for haloantimonates(III) and halobismuthates(III) ferroelectrics characterized by [MX₄]^-, [M₂X₉]^3-, [MX₅]^2-, and [M₂X₁₁]^5- anions is given.

Unexpected hydrolytic transformation of new type hybrid bromobismuthates with methylpyrazinium dications

A series of new type hybrid bromobismuthates formed by various pyrazinium cations were isolated and studied. In the systems initially containing iodide anions and monocations of substituted pyrazines, the complexes based on doubly charged cations of substituted pyrazines instead of ones based on the corresponding monocations were surprisingly formed. The variation of substituted pyrazinium cations affects not only the crystal structures of hybrid bromobismuthates via tuning the nuclearity of the anions but also the hydrolytic stability of the compounds. A thorough structural study of hydrolytic transformations was performed for halobismuthates for the first time. The results revealed a stepwise course of the process affording several products. Spectral studies of the complexes evidence that the values of optical band gaps (E_g) are low in comparison with those for similar systems which is most likely due to the cooperative effect involving the nature of the corresponding cations together with the features of the supramolecular structures of the complexes.

Symmetry breaking structural phase transitions, dielectric properties and molecular motions of formamidinium cations in 1D and 2D hybrid compounds: (NH2CHNH2)3[Bi2Cl9] and (NH2CHNH2)3[Bi2Br9]

Two organic–inorganic hybrid halobismuthates(iii), (NH₂CHNH₂)₃[Bi₂Cl₉] (FBC) and (NH₂CHNH₂)₃[Bi₂Br₉] (FBB), have been prepared with their structures revealed by single-crystal X-ray diffraction at various temperatures.

Investigations of organic–inorganic hybrids based on homopiperidinium cation with haloantimonates(iii) and halobismuthates(iii). Crystal structures, reversible phase transitions, semiconducting and molecular dynamic properties

A description of the thermal, structural, ¹H NMR, electric and optical properties of novel organic–inorganic hybrids.