CrystEngComm最新文献

Two approaches are proposed for obtaining heterospin complexes with an anion-radical of difurazanopyrazine L – a paramagnetic derivative of 4H,8H-bis(1,2,5-oxadiazolo)[3,4-b:3′,4′-e]pyrazine. Aqua 3d metal complexes [ML₂(H₂O)₄]·2H₂O (M = Ni and Co) were synthesized using saturated solutions of reagents with a large excess of M(NO₃)₂. Ammine complexes [ML₂(NH₃)₄] (M = Ni and Cu) were obtained from the reaction of M(NO₃)₂ with NaL(H₂O)₃ in a stoichiometric ratio in the presence of concentrated aqueous ammonia (28%). In all complexes, metal ions coordinate L via N atoms of the pyrazine ring. Molecules of the complexes are linked into a framework by hydrogen bonds. It was found that in [ML₂(NH₃)₄] strong antiferromagnetic exchange interactions are realized between anion-radicals from neighboring molecules, determining the magnetic behavior of the phase as a whole. Whereas in [ML₂(H₂O)₄]·2H₂O, the exchange interactions are ferromagnetic in nature. This is due to the presence of water molecules in the structure, which provide a displacement of the complex molecules relative to each other and, as a consequence, a weakening of the interactions between adjacent L.

Drug discovery and development is an indispensable sector of R&D, and it is of immense significance due to its relevance and direct impact on human life. However, the discovery of new drugs is an evolving and onerous process with critically low success rates, and the majority of potential drugs face physicochemical limitations. Among the known drugs, poor solubility is a serious limitation, and about 90% of discovered drugs and 40% of commercial drugs are class II and IV drugs with poor aqueous solubility. Crystal engineering has appeared as a facile, quicker, and green approach to address the physicochemical limitations of drugs, including their poor aqueous solubility, through a non-covalent strategy involving the development of polymorphs, pharmaceutical co-crystals, and organic salts. This perspective includes a discussion on the definition, classification, and nomenclature of binary crystal forms; a basic understanding of the design method of pharmaceutical co-crystals (ΔpK_a rule, coformer screening, and synthon concept); synthetic methods and scale-up processes of co-crystallization; crystal nucleation; phase diagrams; and opportunities and challenges in the area.

Two-dimensional (2D) layered transition metal dichalcogenides (TMDCs) can form spiral structures via a screw-dislocation-driven mechanism, which leads to changes in their crystal symmetry and layer stackings that generate attractive physical properties different from their bulk and few-layer crystals. However, the controllable growth of 2D spiral TMDC crystals is still challenging, and the width-dependent optical properties of these spiral structures with different widths need to be further studied. Here, we report the controllable growth of high-yield 2D spiral WS₂ flakes through a chemical vapor deposition route via utilizing spin-coated Na₂WO₄ and Na₂MoO₄ powders as the precursors. Systematic characterizations elucidated that these 2D spiral WS₂ flakes consist of triangular monolayer flakes as the bottom part and spiral microribbons with different widths as the upper part, and the microribbons stacked on the triangular monolayer flakes present a width-dependent optical performance. Finally, the growth mechanism of these unique structures is ascribed to the existence of screw dislocations. These spiral TMDC structures are prospective candidates for probing the physical properties of layered materials and exploring novel applications in functional nanoelectronic and optoelectronic devices.

Zn₃P₂, made from earth-abundant elements, is a promising candidate for thin-film solar cells but faces limitations due to difficulties in achieving n-type doping and its large lattice mismatch with commercial substrates and a high thermal expansion coefficient, causing defects and cracks. Graphene substrates can address these challenges thanks to its weak van der Waals interactions with Zn₃P₂ allowing for mechanical transfer of the thin film and strain-free growth. This study compares five graphene substrates for quasi-van der Waals epitaxial (q-vdWe) growth of polycrystalline Zn₃P₂ thin films using molecular beam epitaxy. Surface features like steps and wrinkles on graphene were identified as main nucleation sites for Zn₃P₂, provided the graphene has minimal point defects. The highest-quality thin films, with the largest grain sizes, were grown on H-CVD graphene on the Si-face of 6H-SiC, featuring solely terraces of atomic height. All substrates showed comparable growth windows for crystalline Zn₃P₂, with higher growth temperatures improving crystal quality, as indicated by enhanced photoluminescence. Cryo-cathodoluminescence measurements revealed spatially localized sub-bandgap emissions, potentially linked to localized strain fields at grain boundaries of up to ±3% as identified by cross-sectional transmission electron microscopy. This work provides insights into advantages and drawbacks of utilising q-vdWe to produce Zn₃P₂ thin films for solar cell applications and highlights the effects of graphene substrate choice and growth parameters on Zn₃P₂ film quality.

CaGdAlO₄ (CGA) crystals are promising gain media for ultrafast lasers due to their favorable thermal and optical properties. However, color center defects often introduce unwanted optical absorption, degrading laser performance. This study identifies interstitial oxygen atoms (O_i) as the dominant source of coloration in CGA crystals through a combination of X-ray photoelectron spectroscopy, optical absorption measurements, and density functional theory calculations. The remarkable consistency between the measured and calculated absorption spectra unequivocally identifies O_i as the primary defect responsible for coloration. The incorporation of O_i introduces mid-gap electronic states, leading to strong absorption in the 250–450 nm range and imparting a yellow color. We demonstrate that controlling the atmosphere during polycrystalline synthesis is crucial, i.e., using a reducing atmosphere yields white, defect-free polycrystalline powders, which subsequently enable the growth of high-quality, colorless CGA single crystals via the Czochralski method under a N₂/H₂ mixed atmosphere. This work clarifies the defect origin in CGA and provides an effective strategy for producing high-optical-quality crystals for advanced photonic applications.

A p–n BiOBr/ZnWO₄ (BZ) heterojunction was synthesized and used for the photocatalytic degradation of RhB in aqueous solution under visible-light irradiation. Notably, an optimized 0.15BZ composite (mole ratio) exhibited excellent photocatalytic activity, which is 14.7 times higher than that of bare ZnWO₄. The integration of p–n heterojunction at the interface of hierarchical nanoflake-assembled BiOBr flowers and nanoflake-assembled yolk–shell microspheres of ZnWO₄ can efficiently promote charge separation and migration, thus significantly improving the photocatalytic performance. Electron paramagnetic resonance (EPR) spectra proved that ·OH radicals were the key reactive components. Moreover, a degradation efficiency of 89.8% was maintained after four cycles, representing good durability for the BZ photocatalyst. This work offers a reasonable way for the economic synthesis of heterojunction materials, and the high-efficiency and chemically stable BiOBr/ZnWO₄ heterojunction composite might act as a promising photocatalyst in water purification applications.

In coordination chemistry research, magneto-chiral dichroism (MChD) is a unique phenomenon that occurs via the interaction of light with a magnetized chiral system. Among the various sophisticated spectroscopic techniques, MChD has become a cornerstone for probing electronic transitions in magneto-optical materials. Nevertheless, achieving strong magneto-optical responses remains a significant challenge, both experimentally, in terms of measurable signal intensity, and theoretically, in terms of accurately modelling and predicting MChD from complex electronic structures. The growing research interest in MChD stems from its dual significance: it not only offers insights into the magnetic, electronic, and chiroptical properties of molecular systems but also holds promise for technological applications such as the development of standalone optical readout mechanisms for magnetic information. The chiral heterometallic 3d–4f systems are particularly promising candidates for MChD research. Intrinsic features such as strong spin–orbit coupling, unique electronic configurations, diverse optical transitions, flexible coordination environments, and pronounced magnetic anisotropy create a molecular platform for advancing the understanding and exploration of this fascinating phenomenon. This perspective primarily highlights the current state of MChD properties in a wide range of 3d–4f coordination complexes, distilling key findings that can guide the rational design of systems with enhanced MChD effects. This article concludes by proposing experimental strategies and research directions aimed at deepening our understanding of MChD and advancing its practical applications.

Colour-changing chemical sensors have found important applications in the detection of low concentrations of volatile organic compounds (VOCs). Among the most promising molecular materials are platinum pincer complexes that display rapid colour changes when exposed to a variety of VOCs. In the solid state, these rapid responses have been linked to changes in non-covalent interactions between the platinum pincer molecules and the guest VOCs. To gain a better understanding of the interactions involved, we have studied the manipulation of vapochromic or solvatochromic properties in a series of square planar platinum(II) pincer complexes through structural modification of the monodentate ligand occupying the fourth coordination site. The platinum(II) complexes are based on the 1,3-di(pyridine)benzene tridentate linker (N^C^N) skeleton with the fourth site occupied by a monodentate, anionic ligand L. The formulae of the complexes synthesised are [Pt(N^C(C(O)OMe)^N)(L)] (L = (NCO) (6), (NCS) (7), (OC(O)Me) (8), (OC(O)CF₃) (9), (OS(O)₂CF₃) (10), and (OS(O)₂(C₆H₄Me)) (11)), and the crystalline solids and solutions of these materials have been tested for solvatochromic or vapochromic changes with VOCs including dichloromethane, acetonitrile, diethyl ether, methanol and water. The complexes 6 and 7 crystallised as yellow solids, with no solvent voids in the crystal lattice. Single-crystal X-ray analyses showed that the intermolecular Pt⋯Pt separations were too long for direct Pt⋯Pt interactions. Neither material displayed solvatochromic or vapochromic properties. However, when the fourth ligand was an acetate group, complex 8, the solid displayed vapochromism, changing colour from an orange water-containing crystalline form to an anhydrous yellow form, and a blue form when treated with methanol vapour. A crystal structure analysis showed that in the orange form adjacent pincer molecules were linked together through a hydrogen bonding network involving lattice water molecules, supported by π⋯π stacking interactions. Complexes 9 and 10 both showed solvatochromism, forming a bright yellow solid when crystallised from dichloromethane but forming an orange solid when recrystallised from acetonitrile. Complex 11 displayed both vapochromic and solvatochromic properties. This complex was isolated as a purple solid, turning yellow upon treatment with methanol droplets or vapour, but this colour change could be reversed upon addition of acetonitrile.

The optical floating zone method was utilized to generate a series of single crystals (Lu_1−xTm_x)₃Al₅O₁₂ (x = 0, 0.005, 0.010, 0.015, 0.020), abbreviated as Tm:LuAG. The concentration of activated ions has a considerable impact on luminous material performance. Thus, this research focuses on the effect of Tm³⁺ concentration on the micro-structure and luminescence properties of lutetium aluminum garnet single crystals. According to XRD diffraction data processed using Rietveld refinement, the micro-structure of LuAG single crystals would be distorted by Tm³⁺ doping. When the concentration of Tm³⁺ is 0.015, the lattice symmetry is the lowest. Upon examining the emission spectra of Tm:LuAG, emission peaks of Tm³⁺ ions were identified. Various strengths of emission peaks were seen within the range of 400 to 600 nm, with the peak at 449 nm exhibiting the highest intensity, accompanied by a phenomenon of energy level splitting at this wavelength. The luminescence intensity of the Tm:LuAG single crystal reaches its highest point when the doping concentration is 0.015. As the doping concentration surpasses 0.015, the luminescence intensity gradually reduces, which causes a concentration quenching event. The optimum doping concentration of the sample is 0.015. The Blasse formula yields a critical distance of 20.80 Å in Tm:LuAG single crystals. The reason for concentration quenching in LuAG crystals is that the interaction between the electric dipole and the electric quadrupole of Tm³⁺ ions occurs. Furthermore, when the concentration of Tm³⁺ ions increases, the fluorescence lifetime decreases. Tm:LuAG single crystals have certain application potential in areas such as three-dimensional display and biological imaging.

Here we report a new tetratopic carboxylic acid ligand H₄L1 containing a fluorescent pyrrolo[3,2-b]pyrrole core, and examine its structural chemistry in two solvated forms with amide solvents and a porous strontium(II) MOF. The two solvates H₄L1·2DMF and H₄L1·4DMA exhibit similar hydrogen bonding characteristics at the N-aryl position, but are differentiated by the hydrogen bonding behaviour of the C-aryl position; while the DMF solvate forms a one-dimensional chain via carboxylic acid dimers, the DMA solvate is fully enclosed by solvent molecules occupying all hydrogen bonding sites. The tendency for the electron-rich core to avoid close π⋯π interactions in these solvates is further evident in the structure of poly-[Sr₂(L1)(DMF)₂(OH₂)]·DMF·H₂O 1, a 3-dimensional rod-packed MOF with narrow linear solvent channels. Exchange of the lattice solvent with methanol, with retention of single crystallinity, gives a framework which can be readily desolvated, and exhibits a maximum CO₂ uptake of 8 wt% at 283 K and 1 atm. The ligand is strongly fluorescent in DMSO in its protonated and deprotonated forms and exhibits characteristic solvatochromism, which is pronounced in solution and remains evident, to a lesser degree, in the fluorescent MOF 1.