CrystEngComm最新文献

The segregation of potassium ions during the growth of NBT-KBT (Na_(1−x)/2 Bi_0.5 TiO₃-K_x/2 Bi_0.5 TiO₃) single crystals via the high-temperature solution growth (self-flux) method is challenging. In this context, the present study performs potassium segregation in grown single crystals with varying potassium contents. The incorporation of low potassium content in the grown crystals is confirmed via elemental analysis. Further, a relationship between the initial sodium and potassium concentrations in the solute and their final compositions in the crystal is established. Moreover, the impact of potassium segregation on the structural, piezoelectric, dielectric and ferroelectric properties of the NBT-KBT single crystals is thoroughly investigated. To understand the impact of potassium substitution, structural transformations are analyzed using line profile analysis and Rietveld refinement. Near the morphotropic phase boundary (MPB), the simultaneous presence of rhombohedral and tetragonal phases is observed, leading to a synergistic enhancement of functional properties, such as piezoelectricity, dielectric permittivity, and ferroelectric polarization. Increasing the potassium concentration leads to a rise in the depolarization temperature, implying relatively strong resistance to thermal depolarization. Notably, near the MPB, the piezoelectric and ferroelectric properties reach their maximum, attributed to the structural phase coexistence and optimized domain configurations. Further, the Landau–Devonshire theory describes the temperature-dependent evolution of the ferroelectric behavior, where strong and stable polarization is observed at low temperatures. As temperature increases, domain stability weakens, leading to the emergence of ergodic relaxor characteristics, as reflected by relatively slim P–E loops. These results emphasize the importance of ionic size and domain evolution in enhancing the thermal stability and ferroelectric performance of lead-free NKBT piezoelectrics at the morphotropic phase boundary. These findings provide an effective approach for growing NBT-KBT single crystals with the desired composition and offer insights for optimizing lead-free piezoelectrics for sensor and actuator applications.

The metastable zone width (MSZW) during the cooling crystallization of sulfamethazine–acetylsalicylic acid (SMZ–ASA) cocrystal system in acetonitrile (ACN) exhibits different patterns with variations in coformer ratios and saturation temperatures. Studies were carried out at a fixed 0.3 °C min⁻¹ cooling rate in 20 mL with three agitation rates (100, 400, and 800 RPM), across a saturation temperature range of 15–35 °C with ASA/SMZ molar ratios ranging from 2.5–9.61. Polynomial surface fitting of the induction time data was employed to assess the dependence of MSZW on solute concentration and saturation temperature, where the concentration range was varied between 30–70 mM for SMZ and 100–400 mM for ASA. The results revealed that both coformers' composition and temperature strongly influence MSZW. Importantly, a non-monotonic trend was observed, with the MSZW broadening at higher saturation temperatures for fixed ASA/SMZ ratios, an atypical behavior compared to conventional cooling crystallization. These findings emphasize the system-specific complexity of cocrystal nucleation and the intertwined influence of solute composition and saturation temperature.

“Bridge-flipped isomers” are pairs of organic molecules differing only in the reversal of a bridge of atoms connecting two major parts of the molecules. Among the benzylideneanilines, the isomerism is R–CHN–R′ vs. R–NCH–R′ (R, R′ = aryl). Isomorphous pairs of bridge-flipped benzylideneanilines are rare. This study is focused on pairs of molecularly centrosymmetric bis-benzylideneanilines to determine whether the tendency of centrosymmetric molecules to be located on crystallographic inversion centers, in combination with their overall similarity in molecular space-filling requirements, may promote their isomorphism. A survey of the Cambridge Structural Database for centrosymmetric bridge-flipped bis-benzylideneaniline pairs of the R–CHN–C₆H₄–NCH–R vs. R–NCH–C₆H₄–CHN–R type identified 23 pairs, only two of which are isomorphous. A survey for bridge-flipped diimine pairs of the R–CHN–NCH–R vs. R–NCH–CHN–R type identified six pairs, none of which are isomorphous. Conformational differences attributed to steric interaction between the bridge C–H hydrogen atom and a ring hydrogen atom account for most of the non-isomorphous cases. From examination of whether similar intermolecular packing motifs involving organic fluorine might promote isomorphism between molecularly centrosymmetric pairs, described here are the crystal structures of three pairs of bridge-flipped bis-benzylideneanilines prepared by reaction of 2-(trifluoromethyl)benzaldehyde, 3-(trifluoromethyl)benzaldehyde, and 4-(trifluoromethyl)benzaldehyde with p-phenylenediamine and by reaction of 2-(trifluoromethyl)aniline, 3-(trifluoromethyl)aniline, and 4-(trifluoromethyl)aniline with terephthalaldehyde. The 3-(trifluoromethyl) isomers, located on inversion centers and nearly planar, are isomorphous. Certain bis-benzylideneanilines assume crystal structures isomorphous with those of the corresponding bis-stilbene or bis-azo compound, although whether they do so more readily than with their bridge-flipped isomer has not been determined.

The development of efficient and stable catalysts for ammonia decomposition is crucial for hydrogen production, addressing the challenges of hydrogen storage and transport. Nickel-based catalysts serve as promising alternatives to noble metals, yet they face challenges such as sintering and limited stability. This study focuses on the preparation and performance of Ce–Zr solid-solution-supported Ni-based catalysts to enhance their catalytic activity and durability. For comparison, a Y–Zr–O-supported catalyst was also prepared to elucidate the unique role of the Ce–Zr support. The Ni_2.5/Ce_xZr_1−xO₂ and Ni_2.5/Y_xZr_1−xO₂ catalysts were synthesized via the sol–gel method. XRD confirmed the formation of fluorite-structured Ce–Zr solid solutions (Ce_0.16Zr_0.84O₂, Ce_0.5Zr_0.5O₂, and Ce_0.6Zr_0.4O₂), while the Y–Zr system formed only a Y_0.18Zr_0.82O₂ phase due to its ionic radius mismatch. Characterization techniques including SEM, BET, XPS, H₂-TPR, and TPD revealed that the Ni/Ce_0.6Zr_0.4O₂ catalyst exhibited a high specific surface area (122.35 m² g⁻¹), abundant oxygen vacancies, excellent Ni dispersion, and optimal metal–support interaction. The Ni/Ce_0.6Zr_0.4O₂ catalyst achieved nearly 100% ammonia conversion at 550 °C under a gas hourly space velocity (GHSV) of 12 000 mL g_cat⁻¹ h⁻¹, significantly outperforming the catalysts supported on pure oxides or Y–Zr solid solutions. It also demonstrated high hydrogen production rates and exceptional stability over a 60-hour test with less than 5% activity loss. Its enhanced performance is attributed to the synergistic effects of the Ce–Zr solid solution, which improve the oxygen mobility, stabilize the structure, and facilitate NH₃ activation and N₂ desorption. This work demonstrates an effective strategy for designing non-noble metal catalysts with high efficiency and stability for the industrial decomposition of ammonia.

We have synthesized a series of fluorine substituted 2-methylpropanamide compounds including a pair of polymorphs with the fluorine substitution at the aromatic ring and methyl carbon to investigate the relevance of weak non-covalent interactions in the solid-state. The compounds are structurally characterized using the single crystal X-ray diffraction technique and their supramolecular behaviours are explored methodically regarding the contribution of strong hydrogen bonds like N–H⋯O, acting in conjunction with C–H⋯O, and the ancillary support of weak C–H⋯F interaction. PIXEL calculations allowed for the estimation of the different intermolecular interaction energies of the derived dimers and the overall lattice energies of the different crystalline solids. It is observed that the molecular motifs consisting of C(sp²)–H⋯F–C(sp²) interaction are more stable in comparison to other C–H⋯F interactions. QTAIM analysis further supports these interactions via a topological analysis of the electron density distribution at the bond critical point. A detailed experimental and computational evaluation has been carried out to evaluate the effect of the environment surrounding the carbon atom, i.e. the role of hybridization of the carbon atom, connected to the acceptor fluorine atom and the donor hydrogen atom as well.

Structural reproducibility, in terms of ligand conformation and subsequent predictability, has been explored for five-membered imide-based ligands. Three dicarboxylic acids, based on a pyromelliticdiimide core appended with amino acids, have been synthesised, structurally characterised, and used in the (attempted) synthesis of coordination polymers. The diacids differ in steric bulk at the α-carbon by varying the precursor between glycine (2× H), alanine (1× H, 1× CH₃) and aminoisobutyric acid (2× CH₃). Coordination polymers containing the glycine- and alanine-derived dicarboxylates (GlyPmDI²⁻ and AlaPmDI²⁻, respectively) were synthesised, although none could be isolated containing the most sterically encumbered ligand (ibaPmDI²⁻). The glycine-based coordination polymers show close, parallel stacking of the ligands, whereas the alanine-based coordination polymers do not. The conformation of the coordinating group with respect to the core of the ligand was studied by comparison of crystallographic data and computationally minimised structures. The preferred geometry of the ligand is shown to be dependent on the α-carbon substituents. For each ligand the geometry is reasonably predictable despite the ability of the terminal groups to rotate freely in solution.

Among the various methods for removing carbon monoxide (CO) from hydrogen-rich (H₂-rich) gases, carbon monoxide selective methanation (CO-SMET) has become one of the most effective ones, bringing considerable advantages in terms of performance, environmental sustainability and cost. A bimetallic NiRu/η-Al₂O₃ catalyst with Ni–Ru alloy phases was prepared and its performance in the removal of CO through a selective methanation process was examined in this study. Also, a comparison was made with the NiRu/γ-Al₂O₃ catalyst. The NiRu/η-Al₂O₃ catalyst demonstrated excellent CO-SMET performance, reducing the CO concentration to below 10 ppm with over 50% selectivity between 215 and 300 °C. Its excellent catalytic performance can be ascribed to numerous Ni active sites, increased oxygen vacancies, and more acidic sites. Additionally, the NiRu/η-Al₂O₃ catalyst had the ability to resist sintering because of the formation of Ni–Ru alloy on it. Moreover, it also exhibited good catalytic stability.

The Schiff base ligand, N-salicylidene-2-amino-5-chlorobenzoic acid (sacbH₂), was initially employed in both homometallic Cu^II and heterometallic Mn^II/Cu^II coordination chemistry. A 1-D helical chain, [Cu^II₂(sacb)₂(MeOH)]_n (1), and a decanuclear 0-D heterometallic cluster, [Cu^II₈Mn^II₂(OH)₄(sacb)₈(H₂O)₂] (2), were synthesized and fully characterized. Complex 2 is one of the two highest nuclearity Mn^II/Cu^II complexes reported to date and exhibits a unique {Cu₈Mn₂(μ₃-OH)₄(μ-OR)₆(μ₃-OR)₂(μ-O₂CR)₂}⁶⁺ core composed of two oppositely oriented pentanuclear {Cu₄Mn} units, each featuring two vertex-sharing {Cu₂Mn} triangles. The presence of the {Cu₂(sacb)₂} fragment in both species suggests a templating role of the preformed chain 1 in the assembly of molecular cluster 2. Variable-temperature dc magnetic susceptibility studies reveal predominant antiferromagnetic interactions between Cu^II⋯Mn^II and Cu^II⋯Cu^II centers, with exchange coupling constants: J₁ = −16.5(1) cm⁻¹, J₂ = −35.1(5) cm⁻¹ and J₃ = +0.7(3) cm⁻¹. These findings highlight the utility of preformed oligonuclear and polymeric 3d-metal species as building blocks for the preparation of heterometallic 3d/3d′ polynuclear complexes with novel architectures and tailored physicochemical properties.

Aluminum nitride (AlN) crystals, as a typical representative of wide bandgap semiconductor materials, are being widely used in high-performance power electronics and optoelectronics devices. However, the high-power density of the devices poses new challenges for thermal management, therefore, there is an urgent need to enhance the study of thermal properties of AlN crystals, especially for crystals with different orientations. In this work, (0001) and (10−11) oriented AlN crystals are taken as examples for comparative study. Thermal conductivity is measured from room temperature to 300 °C using a laser flash method. The data within the tested temperature range are fitted, revealing the functional forms of thermal diffusivity and thermal conductivity as a function of temperature. It is found that thermal conductivity is proportional to T⁻ⁿ, where 1 < n < 2, consistent with observations in 4H-SiC and 6H-SiC. The temperature dependent thermal properties are evaluated in both orientations revealing weak anisotropy in thermal conductivity. In addition, various factors affecting the thermal properties of AlN crystals are discussed. These findings provide valuable insights for the development of AlN-based devices.

We introduce a Hirshfeld-volume-driven equation of state (EoS) to resolve atomistic compression mechanisms in diopside (CaMgSi₂O₆) under high pressure (0–10.16 GPa). Our approach integrates topological electron density partitioning via Hirshfeld surface analysis with third order Birch–Murnaghan EoS, achieving <2% error in Hirshfeld volume (V_H) predictions versus experimental benchmarks. Critically, this method visualizes and quantifies how interatomic contacts and crystal packing evolve under compression. Hirshfeld analysis reveals a stark differential atomic compressibility: Mg atoms dominate strain absorption (ΔV_atom/V_atom = −16.2% at 10.16 GPa), followed by Ca (−12.7%), Si (−8.54%), and O (−4.60%). This hierarchy arises from the flexible coordination environments of Mg/Ca–O polyhedra (bulk modulus B₀ ≈ 85 GPa) accommodating compression via bond shortening, while the rigid SiO₄ tetrahedra (B₀ > 150 GPa) preserve the supramolecular architecture. Calibrated Hirshfeld volume-EoS parameters (V_H = 438.72 ų, B₀ = 119.0 GPa, = 3.44) align with experiments (ΔV_H < 0.03%), providing a profound link between microscopic interactions and macroscopic properties. This work establishes the Hirshfeld-driven EoS as a transformative tool for decoding structure–property relationships in molecular crystals and designing pressure-resilient functional materials.