A brief review focuses on studies into the structural reasons for the nonlinear optical properties of crystals of the potassium titanyl phosphate family, performed at the Shubnikov Institute of Crystallography. Accurate X-ray diffraction data are discussed, providing evidence that the optical susceptibility of crystals is related not only to the alternation of long and short Ti–O bonds in the chains of TiO₆ octahedra, but to the geometry of tetrahedral anions and the alkaline cation arrangement in the structure channels, as well. The contribution of each of the three structural components depends on the crystal composition.

The crystal structure of potassium, rubidium, cesium, and ammonium hydrophthalates is analyzed based on the data in the literature. A relationship between their structure and elastic and mechanical...

A precision X-ray diffraction study of Nd5Mo3O16single crystals is performed for the first time at 30 K. Measurements in the range from room temperature to 30K showed that the unit-cell parameters...

The structure of the cubic metastable β_ms phase of La₂Mo₂O₉ single crystal has been precisely investigated by X-ray diffraction at 33 K for the first time. The measurement of the unit-cell parameter of this crystal in the range from room temperature to 33 K showed that the unit-cell parameter and volume change continuously in this range. The crystal has a similar structure at T = 33 K and at room temperature. A local lowering of the symmetry for La and Mo atoms, caused by their displacement, is confirmed, and a similar displacement (which was not observed at room temperature) is revealed for O(1) atoms. The thermal parameters for O(2) and O(3) atoms do not change with a decrease in temperature, in contrast to the thermal parameters of Mo, La, and O(1) atoms. This fact indicates that the O(2) and O3 atoms in this crystal are statically disordered.

Four BODIPY (boron-dipyrrin) dyes with various condensed aromatic moieties (phenyl, naphthyl, anthryl and pyrenyl) as 8-substituents were chosen and their supramolecular organization and properties in Langmuir–Schaefer (LS) films with different numbers of layers were investigated. The spectral characteristics of the dyes in LS-films and solution and the structure of the films were examined. The BODIPY substituent structure influences the character of the intermolecular interactions of the dyes in LS-films. The phenyl-substituted compound was found to form excimers with a long wavelength fluorescence peak at 582 nm upon the layer number increase, yet only minor bathochromic shifts of the peak position were observed for the films of the other investigated compounds. Moreover, unlike in liquid solutions, the dyes in LS-films were not found to exhibit solvatochromic properties. All of the compounds (except anthryl-substituted) were found to retain fluorescence in solid films. Transfer of films from a floating monolayer was indicated by further material analysis: the measured average periodicity corresponds to a single-layer structure of BODIPY molecules located parallel to the surface with an interplanar distance of d = 0.3 nm. The obtained results broaden the prospects of BODIPY based thin film material applications, denoting versatile modification routes leading to increased fluorescence, tunable excimer formation equilibrium and crystallinity.

The literature data and the results obtained by the authors on the study of the structure and properties of a series of polycrystalline and single-crystal samples of pure and Mg-doped oxymolybdates Ln₂MoO₆ (Ln = La, Pr, Nd) are analyzed. Presumably, the high-temperature phase I4₁/acd of Nd₂MoO₆ single crystals is retained at room temperature. The reason for the loss of the center of symmetry in the structures of La₂MoO₆ and Pr₂MoO₆ and the transition to the space group I$\overline{4}$c2 is the displacement of oxygen atoms along the twofold diagonal axes. In all structures, Mg cations are localized near the positions of the Mo atoms, and the splitting of the positions of the atoms of rare-earth elements is found. Thermogravimetric studies, as well as infrared spectroscopy data for hydrated samples of Ln₂MoO₆ (Ln = La, Pr, Nd), pure and with an impurity of Mg, confirm their hygroscopic properties.