ELECTROCHEMICAL POLYMORPHIC PHASE FORMATION IN METALS

The phenomenon of electrochemical phase formation in metals and alloys via a supercooled liquid state stage was discussed. Assuming the electrodeposited metal to be a product of formation and ultrarapid solidification of supercooled metallic liquid, a possibility of metastable phase formation during electrodeposition of polymorphous metals was suggested. It was anticipated that the polymorphic transition of the metal’s metastable form to the stable one occurs by shear, as does the martensitic transformation. To enable revealing an orientation relationship between grains of the two phases, a method for X-ray texture analysis of metals was developed using a combination of direct pole figures. It was established that the phase formation during electrodeposition of polymorphous metals produces metastable modifications typical of entities that crystallized from a liquid state at extremely high rates. In regards polymorphic transitions in metal electrodeposition, certain orientation relationships were observed between grains of the stable and the metastable phase, which is typical of phase transformations proceeding at extremely high rates. The results obtained provided additional arguments in favor of the phenomenon under discussion.

Phase relations in the CuI-SbSI-SbI3 composition range of the Cu–Sb–S–I quaternary system

The phase equilibria in the Cu-Sb-S-I quaternary system were studied by differential thermal analysis and X-ray phase analysis methods in the CuI-SbSI-SbI3 concentration intervals. The boundary quasi-binary section CuI-SbSI, 2 internal polythermal sections of the phase diagram, as well as, the projection of the liquidus surface were constructed. Primary crystallisation areas of phases, types, and coordinates of non- and monovariant equilibria were determined. Limited areas of solid solutions based on the SbSI (b-phase) and high-temperature modifications of the CuI (α1- and α2- phases) were revealed in the system. The formation of the α1 and α2 phases is accompanied by a decrease in the temperatures of the polymorphic transitions of CuI and the establishment of metatectic (3750C) and eutectoid (2800C) reactions. It was also shown, that the system is characterised by the presence of a wide immiscibility region that covers a significant part of theliquidus surface of the CuI and SbSI based phases

Mechanochemical Synthesis of the Catechol-Theophylline Cocrystal: Spectroscopic Characterization and Molecular Structure

Pharmaceutical cocrystallization offers the possibility to modify the physicochemical and biopharmaceutical properties of active pharmaceutical ingredients. The mechanochemical synthesis and spectroscopic characterization of the catechol-theophylline (CAT-TEO) cocrystal is reported. The cocrystal was prepared by the solvent-assisted grinding method. The ATR-IR spectroscopy study allowed to determine the formation of the cocrystal because the O-H and C=O stretching bands in the CAT-TEO cocrystal were shifted with respect to the starting materials, suggesting the formation of the C=O···H-O hydrogen bond interaction. Infrared spectroscopy also allowed to discard hydration of the cocrystal, and polymorphic transitions of the starting products as a consequence of the mechanochemical grinding. The X-ray powder diffraction and thermal studies confirmed the formation of a new solid phase. In the solid state 13C NMR spectra of the cocrystal, the signals were shifted with respect to the starting products. The 13C NMR chemical shifts of the CAT-TEO cocrystal were simulated by using the gauge including the atomic orbital (GIAO) method. These results showed a good correlation between the experimental and calculated 13C NMR results. Theoretical calculations and natural bonding orbital analysis (NBO) at a B3LYP/6-31G(d,p) level of theory were performed to obtain structural information of the cocrystal.

Contribution of C−H⋯π Interactions to Polymorphic Transitions of a Molecular Crystal with Disordered Fragments

Polymorphic transition is important for the functionality of crystalline materials. However, the underlying mechanism remains unclear, especially when the crystal structure contains disordered fragments. We report that C−H⋯π interactions play an important role in polymorphic transitions in a molecular crystal with disordered fragments. The crystal has three phases, namely the a (< -80°C), β (-80-40°C), and γ (< 40°C) phases, which are reversible through single-crystal-to-single-crystal transformation in association with temperature change. Disorder of bulky tert-butyl substituents appears at high-temperature in the β and γ phases. Intermolecular interaction analysis based on Hirshfeld surfaces and related fingerprint plots revealed that the proportion of π⋯π interactions decreased, while that of C−H⋯π interactions increased, at the transition from a to β phase. The proportion of C−H⋯π interactions also increased at the transition from β to γ phase, but continuously decreased in the β phase due to elevated temperature. Intermolecular interaction energies clarified the contribution of C−H⋯π interactions to the stability of high-temperature crystal β and γ phases via polymorphic transitions. Our results potentially lead to design molecular crystals with polymorphic transitions.

Contribution of C−H⋯π Interactions to Polymorphic Transitions of a Molecular Crystal with Disordered Fragments

Polymorphic transition is important for the functionality of crystalline materials. However, the underlying mechanism remains unclear, especially when the crystal structure contains disordered fragments. We report that C−H⋯π interactions play an important role in polymorphic transitions in a molecular crystal with disordered fragments. The crystal has three phases, namely the a (< -80°C), β (-80-40°C), and γ (< 40°C) phases, which are reversible through single-crystal-to-single-crystal transformation in association with temperature change. Disorder of bulky tert-butyl substituents appears at high-temperature in the β and γ phases. Intermolecular interaction analysis based on Hirshfeld surfaces and related fingerprint plots revealed that the proportion of π⋯π interactions decreased, while that of C−H⋯π interactions increased, at the transition from a to β phase. The proportion of C−H⋯π interactions also increased at the transition from β to γ phase, but continuously decreased in the β phase due to elevated temperature. Intermolecular interaction energies clarified the contribution of C−H⋯π interactions to the stability of high-temperature crystal β and γ phases via polymorphic transitions. Our results potentially lead to design molecular crystals with polymorphic transitions.