Crystal Growth & Design最新文献

An investigation of isostructural compounds Bi₁₄MO₂₄, where M is either Cr or Mo, has been conducted under high-pressure (HP) conditions, reaching up to 30 and 40 GPa, respectively. In situ synchrotron X-ray diffraction was employed to monitor alterations in the crystal structure induced by pressure. The compounds have been studied in two different experimental conditions, under hydrostatic conditions using He as pressure transmitting medium (PTM) or under plastic deformation without PTM. Remarkably, the use of helium gas as a PTM revealed isomorphic phase transitions unobserved previously when other PTMs were used. In the case of Bi₁₄MoO₂₄, in addition to the previously documented tetragonal (I4/m) to monoclinic (C2/m) transition, two new isomorphic (monoclinic–monoclinic) phase transitions have been identified. Conversely, Bi₁₄CrO₂₄ exhibits two novel isomorphic (tetragonal–tetragonal) transitions preceding the tetragonal-monoclinic transformation. While analogous phase transitions were identified in experiments performed without PTM, an earlier pressure onset of phase transition was noted. Moreover, a new cubic phase coexisting with HP modification was observed in Bi₁₄CrO₂₄, providing insights into the behavior of these compounds under extreme conditions of shear-stress.

In this study, dehydrofluorinated poly(vinylidene fluoride)/lead zirconate titanate composites (DHF-PVDF/PZT) were prepared via solution casting, followed by hot pressing. The synergistic effect of dehydrofluorination and PZT addition on the polar phase content and electrical properties of DHF-PVDF/PZT was investigated. The polar phase content of DHF-PVDF increases to 60.76% with the introduction of 9.42% carbon–carbon double bonds and then to 84.96% with the addition of PZT. The dielectric and ferroelectric properties of DHF-PVDF/PZT composites are enhanced under the synergistic effect of PZT addition and dehydrofluorination. The dielectric constant of DHF-PVDF/8 wt %PZT at 1 kHz significantly increases (∼16.0) compared to DHF-PVDF (∼11.9), while dielectric loss remains low. DHF-PVDF/8 wt %PZT also exhibits a high discharge energy density (∼6.43 J/cm³ at 2500 kV/cm) and efficiency (∼45.6%), attributed to the strong localized electric field generated in the composites. The study leads toward a way of developing PVDF/PZT composites for high-energy density capacitors.

The work of the English anatomist George Rainey is compared with that of the Dutch naturalist Pieter Harting. While the latter is regarded as a pioneer in biomimetic inorganic crystallography for precipitating unusual crystallographic forms that mimic the products of living organisms, the work of Rainey largely has been forgotten. In fact, Rainey first prepared amorphous calcium carbonate, a material that can be molded by organisms to form biogenic crystals. Rainey’s extensive experimentation with amorphous calcareous bodies observed in a variety of organisms was at one time considered a significant and pioneering chapter in inorganic chemical morphogenesis and it should reclaim some of its former assessments. Rainey’s interpretations of crystal form and the effects of gravity on crystal growth mechanisms, however, are historical curiosities that should be left behind, except to the extent that they show how the efforts of an individual may appear diminished by the dynamic process of consensus building in science. Harting also prepared amorphous calcium carbonate, but more than a decade after Rainey. While Rainey was a quiet scholar with steady habits, Harting was a statesman, a champion of the down-trodden (albeit with prejudice), a popular educator, a temperance advocate, and a sci-fi novelist, in addition to being a professor. Harting’s public life may account for his outsized place in our collective memory. Rainey’s synthesis of amorphous calcium carbonate in the presence of gum arabic was repeated in a modern setting. Microspheres were characterized by scanning electron microscopy, established as hollow by X-ray microtomography, and were shown to have the composition of calcium carbonate by energy dispersive X-ray analysis. They were amorphous by powder X-ray diffraction.

George Rainey (1801−1884), an anatomist at St. Thomas’s Hospital in London, first described the preparation and crystallization of amorphous calcium carbonate.

The truncated geometry of the liquid–solid interface in Si, Ge, and zincblende III–V nanowires grown by the vapor–liquid–solid method has far-reaching implications in the nanowire morphology, crystal phase, and doping process. It has previously been found that the amount of truncation oscillates in synchronization with the monolayer growth cycle, which was explained within a model of Tersoff and coauthors. Here, we develop an advanced model for the oscillations of the truncated geometry in vapor–liquid–solid nanowires and study in detail different stages of monolayer growth in nanowires with such a geometry. It is shown that the large truncated volumes (on the order of one monolayer) observed experimentally in different nanowires are due to the stopping effect upon reaching zero supersaturation in a catalyst droplet. This effect is specific for small droplets, which do not contain enough material at nucleation to grow a whole monolayer from liquid. Upon reaching zero supersaturation of the liquid phase, the monolayer growth rapidly continues by taking the required amount of material from the truncation, which explains the rapid increase in the truncated volume after the stopping size. In growth conditions without a stopping size, the calculated truncation volumes are much smaller and may be even unphysically small for GaAs and other III–V nanowires. The model is applied to self-catalyzed zincblende GaAs nanowires and Au-catalyzed Si nanowires and compared to the available experimental data.

Ethionamide (ETH) is a second-line antituberculosis drug, but its aqueous solubility is poor. A cocrystal/salt screen of ETH with fluorobenzoic acid (FBA) coformers afforded four cocrystals and one salt of ETH, namely, ETH-4-fluorobenzoic acid (4FBA, cocrystal), ETH-3,4-difluorobenzoic acid (34DFBA, cocrystal), ETH-2,4,5-trifluorobenzoic acid (245TFBA, cocrystal), ETH-2,3,4,5-tetrafluorobenzoic acid (2345TFBA, cocrystal), and ethionamidium-2-fluoro-6-hydroxybenzoate (2F6HBA, salt). The new crystalline multicomponent cocrystal-salt (MCCS) forms were characterized by powder X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, single crystal X-ray diffraction, and FT-IR analysis. Structural analysis showed that the acid-pyridine, hydroxyl-pyridine, and thioamide dimer synthons stabilize ETH cocrystals/salt structures. The cocrystals/salt exhibit remarkable improvement in solubility, dissolution, and diffusion at pH 7 in phosphate buffer solution. The ability of fluoro compounds to increase membrane diffusion and bioavailability of drugs as MCCS complexes may be of general applicability for poor solubility and permeability drugs.

One-step purification of acetylene (C₂H₂) from carbon dioxide (CO₂) using CO₂-selective adsorbents is urgently needed but strategically challenging due to their similar physicochemical properties. In this work, we designed a series of isostructural flexible porous coordination polymers (PCPs) modulating the gate-opening pressure for C₂H₂ through linker substitution, preserving high CO₂ uptake at low pressure, and enabling a customizable inverse selectivity of CO₂/C₂H₂. By exploring both pillar and capping ligand substitutions, we found that pillar-ligand substitution in the PCPs allows rational control of the gate-opening behavior for C₂H₂ to achieve highly selective adsorption of CO₂ while discriminating C₂H₂, achieving high CO₂/C₂H₂ uptake ratio (8.5) and selectivity (232.5), which are comparable to other benchmark materials. Furthermore, dynamic breakthrough experiments suggest that our PCPs effectively achieve an inverse CO₂/C₂H₂ separation at 298 K and 1 bar. Consequently, high-purity C₂H₂ (>99.5%) could be obtained from the CO₂/C₂H₂ mixture through a simple one-step column purification. Combining crystallographic structural analyses, we found that the significant structural deformation differences after pillar-ligand substitution compared with capping ligand substitution can rationally control the gate-opening behavior. This simple design strategy allows for reasonable control of the gating behavior of porous materials.

We report here the self-assembly of a fully protected l-3,4-dihydroxyphenylalanine (Boc-l-Dopa(Bn)₂-OMe) under several conditions. Depending on the organic solvent or solvent mixture, this simple molecule self-assembles into different supramolecular structures, sometimes behaving as a low-molecular-weight gelator. Indeed, we observed the formation of organogels in alcohols, as confirmed by rheological analyses. In contrast, in solvent mixtures, long crystalline fibers were formed, and we could obtain single crystals suitable for X-ray diffraction analysis through a vapor diffusion technique. The deep X-ray diffraction analyses allowed us to determine the structure of the crystals, of the gels, and of the fiber-like aggregates and to deduce that the molecule always self-assembles like antiparallel β-sheets, driven by intermolecular hydrogen bonding and π–π stacking interactions.

The diketonate complexes M(acac)₂ (M = Pd (1), Pt (2)) were cocrystallized with bis(perfluoropyridin-4-yl)tellane (Py^F₂Te). Single-crystal X-ray studies of the resulting adducts revealed that the binding mode and stoichiometry between the coformers dramatically depend on the identity of metal sites. Pd(acac)₂ formed adduct 1₃·(Py^F₂Te)₂ where Te···C_acac and π_hole···Pd noncovalent interactions were detected. In contrast to 1, Pt(acac)₂ formed adduct 2·Py^F₂Te where the Te···Pt metal-involving chalcogen bond was observed. Various DFT methods, including the calculation of fully optimized dimeric assemblies and their mutated dimers, allowed for a detailed examination of the corresponding metal-involving noncovalent interactions. Our findings support the notion that metal-involving interactions are the primary structure-determining factors, and the formal transition to the Te···Pt chalcogen bond can be attributed to the increased d_z²-nucleophilicity of the platinum atom compared to the palladium site.

A cyclic triamide of 2,5-dibromo-4-ethylaminobenzoic acid, which has a fixed axial chirality, was prepared in racemic and enantiopure forms. The structures of the corresponding crystals and homochiral molecular assembly formation were analyzed from the viewpoint of intermolecular interactions. Although the packing arrangements in the two types of crystals were similar, the packing difference suggested the importance of the C═O···Br–C contact for the chiral assembly. A statistical analysis of amides with the above contact revealed a correlation between the molecular assembly type (hetero- or homochiral) and the contact angle of adjacent molecules interacting through C═O···Br bonding. Specifically, in the absence of aryl groups, the O···Br–C angles closer to 180° facilitated the assembly of molecule pairs into a chiral arrangement. In contrast, the opposite trend was observed in the presence of one or more aryl groups. Furthermore, the chiral and racemic crystals displayed different preferences for the C═O···Br angle, indicating its importance in determining crystal chirality. Our approach extended the scope of the previously reported method and demonstrated its applicability to compounds with other skeletons.