A number of new solid polyiodides of thia- and oxa-zinoquinolinium derivatives have been characterized using a combined approach of Raman spectroscopy and periodic 3D calculations of the Raman intensities. Various cation–anion ratios, including tri- and polyiodides of the complex structure [I₃⋯I₂]⁻, have been studied. For the oriented single crystal containing the [I₃⋯I₂]⁻ fragments, the polarized Raman spectra and the angular dependency of the band intensities on crystal rotation have been obtained. These techniques have allowed us to get new information on the spatial organization of the intermolecular interactions of iodine in polyiodide-anion chains. They have also shown perspectives on the geometrical characterization of complex polyiodides using Raman spectroscopy.

The interrelation between noncovalent bonds and physicochemical properties is in the spotlight due to the practical aspects in the field of crystalline material design. Such study requires a number of similar substances in order to reveal the effect of structural features on observed properties. For this reason, we analyzed a series of three substituted thiazolo[2,3-b][1,3]thiazinium triiodides synthesized by an iodocyclization reaction. They have been characterized with the use of X-ray diffraction, Raman spectroscopy, and thermal analysis. Various types of noncovalent interactions have been considered, and an S…I chalcogen bond type has been confirmed using the electronic criterion based on the calculated electron density and electrostatic potential. The involvement of triiodide anions in the I…I halogen and S…I chalcogen bonding is reflected in the Raman spectroscopic properties of the I–I bonds: identical bond lengths demonstrate different wave numbers of symmetric triiodide vibration and different values of electron density at bond critical points. Chalcogen and halogen bonds formed by the terminal iodine atom of triiodide anion and numerous cation…cation pairwise interactions can serve as one of the reasons for increased thermal stability and retention of iodine in the melt under heating.

The behaviours of the open pore (op) and closed pore (cp) phases of the flexible Ni₂(ndc)₂(dabco) (ndc – 2,6-naphthalene dicarboxylate, dabco – 1,4-diazabicyclo[2.2.2]octane, DUT-8(Ni)) metal–organic framework under high hydrostatic pressures up to 10 GPa in isopropanol and silicone oil were studied by Raman spectroscopy. Ab initio simulations of vibrational spectra were performed for the open and closed pore phases, which allowed us to disclose the characteristic vibrational modes affected by the structural transitions under pressure. Analysis of theoretical and experimental Raman data suggests that the op–cp transition involves gateway vibrations at 25 and 67 cm⁻¹, corresponding to trampoline/rotational motions of aromatic linkers. The experiments reveal the formation of new distorted cp phases at pressures higher than 2 GPa, which are formed without amorphisation. The transition between the cp phase and the distorted cp phase is reversible. The experiments also reveal the pivotal role of the pressure transmitting medium on the phase transition behaviour.

Structural transformations of metal-organic frameworks (MOFs) go through a complex energy landscape with multiple intermediate states. Although the transformations allow controlling the functional properties of the MOFs, an imbalance between MOF flexibility and rigidity sets a fundamental barrier to achieving fast and multiple transformations. Here, we study the stimuli-responsive structural transformation in a 2D MOF assembled from paddle-wheel secondary building units joined by a semi-flexible organic ligand with 1,2,4-triazole and carboxylate groups with a rigid adamantane cage between them. The structure results in a distinctive combination of MOF flexibility and rigidity, thus, facilitating a continuous transformation driven by laser light. We reveal the laser-induced anisotropic thermal expansion nature of such transformation, initiating optical changes of the 2D MOF. The latter is utilized for fast and highly repeatable optical modulation of over 10,000 cycles. The endurance of such a 2D MOF-based optical modulator during 1 year of storage at ambient conditions paves the way to design tunable and robust MOFs for diverse applications.