The lone-pair-electron-driven phase transition and order-disorder processes in thermochromic (2-MIm)SbI4 organic-inorganic hybrid

The easy to prepare and stable in air (2-methylimidazolium) tetraiodoantimoniate(iii) single-crystals with optical band gap of 2.17(1) eV at room temperature have been synthesized. The crystal structure features one-dimensional [SbI₄]^-_n anionic chains, which are intercepted with stacks of 2MIm⁺ ions. At 294/295 K, it undergoes a structural phase transition to an incommensurately modulated phase as a result of subtle, lone-pair-electron-driven distortions of the anions. Separately from the anion displacements, the ordering of 2MIm⁺ countercations takes place over a wide temperature range of the modulated phase. The disorder changes from dynamic to static around 200 K, which affects the crystal structure leading to discontinuities and step-like contraction of the lattice parameters. The material is thermochromic with prominent color changes, from raspberry to yellow at low temperatures. The calculated electronic structures and observed optical properties signify its semiconducting character.

Fourier transform infrared and Raman spectroscopy in the study of phase transitions in dipyrazolium iodide triiodide: Experimental and theoretical analysis

The paper presents the Infrared and Raman spectra of the powdered [C₃N₂H₅⁺]₂[I^-∙I₃^-] crystal at the temperature intervals of 11-270K, covering two low-temperature phase transitions: discontinuous at 182/188K (cooling/heating) and continuous at 254K. The research shows that the vibrational states of the pyrazolium cations change significantly during discontinuous phase transition (III→II), while the continuous nature of successive structural transformation is more subtle and displays an insignificant change in the temperature coefficient of numerous vibrations during the II→I PT at 254K. The spectacular changes at Raman spectra above 188K confirm a huge rebuilding of inorganic network from [I^-∙I₃^-] to [I₄^2-]. Additionally, a complete geometry optimization was carried out in the solid state in order to obtain minimum structures and bonding properties. The theoretical results correspond well with the experimental data. Moreover, the infrared spectrum in harmonic approximation was calculated, and a comparative vibrational analysis was performed. CRYSTAL09 vibrational results appear to be in a good agreement with the experimental ones.

Structure–property relationships in hybrid (C3H5N2)3[Sb2I9] and (C3H5N2)3[Bi2I9] isomorphs

Two hybrid crystals imidazolium iodoantimonate(iii) and iodobismuthate(iii) have been synthesized and characterized in a wide temperature range (100–350 K) by means of X-ray diffraction, dielectric spectroscopy, proton magnetic resonance, FT-IR spectroscopy and optical observations.

Periodic and incommensurately modulated phases in a (2-methylimidazolium)tetraiodobismuthate(iii) thermochromic organic–inorganic hybrid

Incommensurately modulated crystal structure of a (2-methylimidazolium)tetraiodobismuthate(iii) thermochromic organic–inorganic hybrid.

Unprecedented transformation of [I−·I3−] to [I42−] polyiodides in the solid state: structures, phase transitions and characterization of dipyrazolium iodide triiodide

Dipyrazolium iodide triiodide, [C₃N₂H₅⁺]₂[I⁻·I₃⁻], has been synthesized and studied by means of X-ray diffraction, differential scanning calorimetry, dielectric measurements, and UV-Vis spectroscopy.