CrystEngComm最新文献

This work reports, for the first time, a systematic study of the sonochemical synthesis of sodium titanates under controlled pH conditions, elucidating how the reaction medium governs phase selectivity, morphology, and electrical behavior. Sodium titanate powders were obtained via ultrasonic irradiation with pH values ranging from 2 to 14 and characterized by X-ray diffraction, FTIR, UV–vis spectroscopy, scanning electron microscopy, and impedance spectroscopy. Rietveld refinement demonstrated that the crystalline phases evolve markedly with pH: acidic media (pH 2–6) produce multiphase mixtures of Na₂Ti₆O₁₃ + TiO₂ + NaCl, moderately alkaline conditions (pH 8–10) yield biphasic Na₂Ti₆O₁₃/Na₂Ti₃O₇ with a maximum Na₂Ti₆O₁₃ content of 67 wt% at pH 10, and strongly alkaline synthesis (pH 14) stabilizes Na-rich Na₁₆Ti₁₀O₂₈ (79 wt%). UV–vis spectra revealed optical band gaps from 2.62 to 3.78 eV, and SEM analysis showed a transition from aggregated nanograins to well-defined microrods at pH 10. Impedance spectroscopy confirmed that the sample obtained at pH 10 exhibits the highest ionic conductivity (σ_DC = 9.52 × 10⁻⁴ S cm⁻¹), attributed to the predominance of tunnel-type Na₂Ti₆O₁₃. These results demonstrate that pH control within a sonochemical route represents a new and effective strategy to direct the formation of layered, tunnel, and Na-rich titanates, providing a fast, low-cost, and reproducible pathway for tailoring the structural and functional properties of sodium-based materials for energy applications.

The development of stimuli-responsive smart molecular crystals that maintain their structural integrity under mechanical stress is essential for advancing smart, functional, and adaptable crystalline materials. To achieve a combination of mechanical flexibility and acidochromism in molecular crystals, we designed two benzylideneindanone derivative-based crystals, referred to as crystals 1 and 2. Crystal 1 exhibits 2D elasticity on the (011) and (010) faces, resulting from isotropic packing features within an anisotropic layered structure. In contrast, both crystals 1 and 2 demonstrate 1D plastic behavior on the (011) face, attributed to layer migration under applied stress within the short-range domain of the crystals. Additionally, both crystals 1 and 2 show reversible acidochromism in response to acid vapor. Unlike most acid-responsive crystals that become brittle when exposed to acid, our crystals retain their mechanical flexibility while undergoing color changes in the presence of acid vapor. This unique combination of mechanical resilience and chromic response expands the potential applications in dynamic molecular crystals, including chemical sensing, reversible security tagging, and mechanically adaptive devices.

Efficient thermal decomposition of energetic materials is crucial for solid propellant energy release, yet conventional catalysts suffer from bottlenecks such as insufficient exposure of active sites and poor thermal stability. In this paper, we have synthesised four Pb(II)-based metal–organic frameworks (MOFs), Pb-MOF, Pb-MOF-1, Pb-MOF-2, Pb-MOF-3, using a solvent engineering strategy, and have investigated the evolution of different solvent-regulated crystalline morphologies by XRD and SEM, and the XPS reveals that the binding energy of the Pb–O bond is significantly reduced to 529.7 eV, which forms the electron-rich oxygen species, enhancing its catalytic ability. After the modulation of morphology, the activation energy of RDX is reduced by 50.2%, and the critical explosion temperature is increased by 21.98 °C. The Pb-MOF samples show excellent performance in catalysing the thermal decomposition of RDX. In this study, we investigate the directional evolution of MOF morphology, establish a new mechanism of morphology regulation, and provide a new methodology for the catalytic preparation of MOFs.

The role of halide anion identity and the influence of reaction solvent on the resulting halogen-bonded assembly was explored by combining 1,4-diiodo-tetrafluorobenzene (p-F₄DIB) with trimethylbenzyl ammonium halides (NMe₃BzX, X = Cl, Br, I) in diverse organic solvents. Iodide salts predominantly yielded solvated crystalline products when the salt cocrystallized in an equimolar ratio with p-F₄DIB. In solvent systems where the iodides did not crystallize as solvates, the salt:organoiodine ionic cocrystal ratio departed from the 1 : 1 reaction stoichiometry, producing 8 : 3, 4 : 5, or 2 : 3 cocrystals. In contrast, bromide and chloride analogues favored unsolvated forms, with chloride consistently producing a single 1 : 1 motif across multiple solvents. A small number of solvated forms were isolated in the Br and Cl series, typically at matched donor : acceptor ratios. Notably, chloride and bromide salts formed nearly indistinguishable halogen-bonded networks, apart from differences attributable to anion size. These results emphasize the delicate balance between solvent, stoichiometry, and halide identity in directing halogen-bond-driven crystallization.

Herein, terahertz time-domain spectroscopy (THz-TDS) is used to measure the terahertz spectra of methylparaben (MeP) in the frequency range of 0.5–3.0 THz at different temperatures of 300 K, 330 K, 360 K, and 390 K. Theoretical calculations were conducted using the quasi-harmonic approximation (QHA) method at temperatures of 180 K, 240 K, 300 K, and 360 K. The influence of temperature on the terahertz response of MeP molecules was explored in depth. Both the experimental and theoretical results indicate that as the temperature increases, the terahertz spectrum of this frequency band tends to shift towards the low-frequency region. To further explore the mechanism of this phenomenon, we further used the VMARD method combined with atomic displacement maps to allocate and analyze the vibration modes of each absorption peak at different temperatures. The results indicate that with changes in temperature, there are significant differences in the dominant mechanisms and motion distribution characteristics of each vibration mode, but their motion is still mainly concentrated in the rotational motion of molecules or functional groups. In addition, we used an independent gradient model based on the Hirshfeld partition (IGMH) method combined with atoms in molecules (AIM) theory to explore the effect of temperature on weak interactions in MeP crystals. It was found that the strength of hydrogen bonds varies with temperature, which in turn affects the basic characteristics of weak interactions. This study not only deepens the understanding of the thermodynamic behavior of MeP molecules, but also provides an important theoretical basis and technical support for the thermal stability regulation of materials in the food, cosmetics, and pharmaceutical industries.

Additive-mediated regulation of calcium phosphate phase transitions is critical for synthesizing bone-like mineral structures in vitro. The main calcium phosphate phases involved in mineralization include amorphous calcium phosphate (ACP), dicalcium phosphate dihydrate (DCPD), octacalcium phosphate (OCP), and hydroxyapatite (HAp). This paper reviews the role of additives in these phase transitions. Additives are often adsorbed onto calcium phosphate surfaces, inhibiting transitions from ACP, DCPD, and OCP to HAp. Additives can act as nucleation templates or reduce particle size, promoting the transition from ACP to HAp. The concentration and addition timing of additives significantly influence their role in the ACP-to-HAp transition. Surface energy, incorporation of additives, and interactions with ions in solution also play an important role in calcium phosphate phase transitions.

A controlled two-step approach for generating furosemide polymorphs through multicomponent crystal formation followed by desolvation was investigated. Furosemide was crystallised with five pyridine derivatives—pyridine (FUR·PYRw), 3-picoline (FUR·3PIC), 4-picoline (FUR·4PIC), 2,3-lutidine (FUR·23LUT), and 2,4-lutidine (FUR·24LUTw)—using slow evaporation and liquid-assisted grinding methods. Single-crystal X-ray diffraction analysis revealed 1 : 1 drug : coformer stoichiometry in all structures, while infrared spectroscopy confirmed the protonation states. Thermogravimetric analysis revealed solvent content and additional water inclusion in the pyridine and 2,4-lutidine crystals, while thermal behaviour was monitored using differential scanning calorimetry. Powder X-ray diffraction indicated that FUR·3PIC, FUR·PYRw and FUR·23LUT single crystals represent the bulk crystallisation batch, whereas crystals of FUR·4PIC and FUR·24LUTw showed differences with the bulk. The five multicomponent crystals were desolvated at ambient temperature and pressure for at least six months, then dried over silica gel desiccant for another two months. FUR·3PIC crystals showed excellent stability over eight months, and no changes in the crystal structure were observed. The desolvation of FUR·4PIC resulted in the physical mixture of known furosemide polymorphs, while the desolvation of crystals of FUR·23LUT, FUR·24LUTw, and FUR·PYRw resulted in three new solid forms, which must still be fully characterised.

Mechanochemical preparation of multi-component systems, such as cocrystals and salts, is at the forefront of crystal engineering, driven by its dual benefits of environmental friendliness and efficient material exploration. The intrinsic relationship between mechanochemical milling and supramolecular chemistry arises from the solvent-free nature of the milling process. This study reports the new salts of antifibrinolytic agents, aminocaproic acid (ACA) and aminomethylbenzoic acid (AMA), with various coformers, namely oxalic acid (OXA), tartaric acid (TAT), caffeic acid (CAF), 2-chloro-4-nitrobenzoic acid (CNB), saccharin (SAC), and orotic acid (ORA). Additionally, the crystal structure of the anhydrous AMA compound was determined and reported in this work. The crystal structures of the developed salts were elucidated using single-crystal X-ray diffraction analysis and further analysed by spectroscopic (FT-IR) and thermal methods (DSC and TGA). The salts of ACA with OXA resulted in two solid forms with varying stoichiometry of water molecules (ACA–OXA–H₂O (1 : 1 : 2); ACA–OXA–H₂O (1 : 1 : 1.5)), while ACA–CAF–H₂O was obtained in a 3 : 2 : 2.6 stoichiometric ratio of ACA, CAF, and H₂O in the asymmetric unit. AMA–TAT and AMA–CNB were obtained as hydrates, while AMA–OXA, AMA–SAC, and AMA–ORA were obtained as anhydrous salts. Bulk quantities of ACA and AMA salts were synthesised using both solution-based and mechanochemical ball milling techniques. Unlike conventional solution-based approaches, which typically consume significant amounts of solvents and energy, this study highlights the influence of various ball milling parameters, such as milling media, ball size, frequency, and duration, under both solvent-assisted and neat grinding conditions for the preparation of multicomponent solids of ACA and AMA. A linear correlation was observed between the percentage completion and milling frequency of the ball mill, as well as the time required for completion of the salification process. Interestingly, the different hydrate forms of ACA–OXA (ACA–OXA–H₂O (1 : 1 : 2) and ACA–OXA–H₂O (1 : 1 : 1.5)) were prepared in bulk quantities by ball milling, by fine-tuning the milling parameters, whereas the solvent-based slurry method resulted in only the ACA–OXA–H₂O (1 : 1 : 2) form.

Previous studies have shown that particle size and core–shell structure have a great impact on the electromagnetic parameters and microwave absorbing performance of materials. Here, ZnFe₂O₄ nanoparticles with a particle size of approximately 4 nm were successfully synthesized using a magnetic field-assisted steam–thermal method at 120 °C. The synthesized ZnFe₂O₄ nanoparticles were coated with silica (SiO₂) and carbon (C). The ZnFe₂O₄@C composite exhibited significantly superior microwave absorption performance, attaining a strong absorption peak of −46.2 dB at 8.80 GHz. We conducted a systematic investigation on their microstructures, electromagnetic parameters and microwave absorption performance. These results not only shed light on the understanding of interfacial effects induced by high-density interfaces formed by ultra-fine particles within the coating but also provide an appealing mode for the implementation of heterogeneous interfacial engineering using coatings.

This study successfully achieved the growth of heavily nitrogen-doped polycrystalline silicon carbide (poly-SiC) crystals via the physical vapor transport (PVT) method. Notably, poly-SiC crystals with a low resistivity of 12 mΩ cm were obtained through process optimization, demonstrating significant advancement in electrical performance. The systematic investigation focused on three critical aspects – growth temperature, chamber pressure, and post-growth wafer processing – with their synergistic effects on crystal quality comprehensively demonstrated through resistivity mapping, polytype characterization and growth rate analysis. Experimental results revealed that temperature predominantly governs the resistivity of nitrogen-doped poly-SiC through doping efficiency. By implementing a specially designed parameter decoupling strategy involving orthogonal experimental arrays and furnace structural modifications, we effectively resolved the complex inter-dependencies among temperature and pressure. By developing an advanced PVT method with low cost and easily controlled growth conditions, low-resistivity poly-SiC wafers can be produced and processed as a material for wafer bonding application.