Crystal Growth & Design最新文献

A 0.85:0.15 cis:trans diastereoisomeric mixture of 1,4-bis(diphenylhydroxymethyl)cyclohexane has been shown to form host–guest inclusion compounds with pyridine (PYR) and the three isomeric methylpyridines (2MP, 3MP, 4MP). Diastereoisomeric mixtures of the host compound were found in the crystalline products, but with the trans isomer dominating, ranging from 69% for PYR to 97% for 4MP. Crystals selected from these mixtures for SCXRD analysis were found to comprise the cis host species (H1) for PYR and 3MP and the trans isomer (H2) in the case of 2MP and 4MP. Thermal experiments established that the most stable inclusion complex is obtained with PYR because its release occurs at a higher temperature compared with the three MPs in their respective complexes. In mixed solvent crystallization experiments, the host was usually selective toward PYR, unsurprising given that the PYR complex is the most stable of the four. We therefore suggest that this host compound has potential to separate binary mixtures of the guest solutions considered here. SCXRD analysis also established that the (guest)N···H–O(H1) hydrogen bond is shorter for PYR than the MPs, which is consistent with the higher selectivity of the host species observed for PYR. Hirshfeld surface analyses revealed more extensive C···H/H···C and H···N/N···H interactions between PYR and the host compared compared to the host–guest complexes of the MPs. The crystal structure determination on H1·2(PYR) furthermore revealed that the cyclohexyl ring adopts the unexpected boat conformation. Conformational analysis of H1·2(PYR) as well as the individual host compounds was performed through molecular modeling at the molecular mechanics (MMFF) and DFT (ωB97X-D/6-31G*) levels. This established that when the diastereoisomeric host mixture is crystallized from PYR, a comparatively high-energy host–guest complex is preferred, with a high-energy boat conformer of cis-1,4-bis(diphenylhydroxymethyl)cyclohexane being selected.

The cyclohexyl moiety of the host compound 1,4-bis(diphenylhydroxymethyl)cyclohexane adopted a higher energy boat conformation in its complex with its preferred guest species, pyridine.

Solvothermal reactions of cyclophosphazene-based hexacarboxylate (H₆L) and rigid N-donor ligands (phen = phenantroline, trp = 2,2′:6′,2″-terpyridine, 2,2′-bpy = 2,2′-bipyridine, 4,4′-bpy = 4,4′-bipyridine) resulted in four novel Cd(II) metal–organic frameworks (MOFs), formulated as ([(CH₃)₂NH₂]⁺)[{Cd₆(phen)₂(L)₂(HCOO)(H₂O)}]·4DMF·3H₂O (PCP-3), {Cd₂(trp)₂(H₂L)}]·DEF·2H₂O (PCP-4), [{Cd₃(2,2′-bpy)₂(L)(DMF)(H₂O)}]·2DMF (PCP-5), and [{Cd₆(4,4′-bpy)₂(L)₂(H₂O)₉}]·5DMF·H₂O (PCP-6). These MOFs have been successfully characterized using Fourier-transform infrared spectroscopy (FTIR), single crystal and powder X-ray diffraction (SC and PXRD), thermal analyses (TGA), scanning electron microscopy (SEM), ultraviolet–visible diffuse reflectance measurements (UV-DRS), and solid-state photoluminescence measurements. SCXRD results indicated that the cyclotriphoshazene ligand in MOFs coordinates with Cd(II) ions to give a wide variety of structures ranging from a one-dimensional (1D) tubular structure to three-dimensional (3D) porous frameworks. PCP-3 shows a 3D framework with two secondary building units (SBUs) constructed from trinuclear Cd(II) clusters. PCP-4 has a porous π–π stacking framework constructed from the 1D tubular channels through strong face-to-face π–π interactions. PCP-5 displays a two-dimensional (2D) layered framework. PCP-6 exhibits a 3D porous framework in which pillar 4,4-bpy ligands coordinate with Cd(II) ions. After the removal of guest molecules, PCP-3, PCP-4, PCP-5, and PCP-6 have substantial free volumes, which are 21.04, 17.3, 17.0, and 27.3%, respectively. All PCPs demonstrated high efficiency in photocatalytically degrading four organic dyes: methylene blue (MB), methyl orange (MO), rhodamine B (RhB), and reactive orange 16 (RO16) under UVA light irradiation. A proposed photocatalytic mechanism, based on trapping experiments, identified the O₂^•– and ^•OH as the primary reactive radicals involved in dye degradation. PCPs exhibited remarkable photocatalytic activity, achieving up to 95% degradation efficiency within 40 to 60 min. Additionally, PCPs showed excellent reusability and maintained efficiency over five consecutive runs. In addition, the thermal and photoluminescence characteristics of PCPs were thoroughly examined.

In an attempt to reveal the hydrogen bond-accepting abilities of coordinated water, a survey of Cambridge Structural Database crystal structures yielded 1229 hydrogen bonds between free water as a hydrogen bond donor and coordinated water as a hydrogen bond acceptor. These hydrogen bonds can be divided into two major groups: short linear and long nonlinear hydrogen bonds, the former being more frequent. It was revealed that the short linear hydrogen bonds of acceptor-coordinated water are longer than the hydrogen bonds of donor-coordinated water, which suggests that they are weaker. DFT calculations at the B97D/def2-TZVP level demonstrated that these interactions usually do not surpass the energy of the hydrogen bond between free water molecules (−5.02 kcal/mol) since electrostatic potentials on coordinated water oxygen are less negative than the one on free water oxygen. However, if hydrogen bonds of acceptor-coordinated water are accompanied by substantial secondary interactions, then the interaction can be stronger. The strongest calculated interaction involving a neutral transition metal complex has the energy of −9.31 kcal/mol; these interactions become stronger if complexes are negatively charged, reaching the energy of −13.19 kcal/mol. Long nonlinear hydrogen bonds of acceptor-coordinated water appear only as additional interactions to other hydrogen bonds (short and linear). This study shows that hydrogen bonds of acceptor-coordinated water are abundant in crystal structures and can provide significant stabilization to supramolecular systems with metal complexes, despite them being weaker than hydrogen bonds of donor-coordinated water.

Because of the similar physical properties of acetylene (C₂H₂) and carbon dioxide (CO₂), their efficient separation remains challenging in industry. In this work, two isomeric ultra-microporous Fe-isonicotinate frameworks (SNNU-131 and SNNU-132) were prepared by a cluster-aggregation strategy, and both show prominent acetylene and carbon dioxide adsorption and separation ability. The linear trinuclear cluster [Fe^III₂Fe^II(μ₂-O)₂(COO)₄] and its dimer, hexanuclear cluster [Fe^III₄Fe^II₂(μ₃-O)₂(μ₂-O)₂(COO)₈] were extended by isonicotinic acid linkers to generate two 8-connected supramolecular isomers with typical bcu and hex topology, respectively. Thanks to the existence of 1D quadrilateral channels with crossing size of about 7 Å and open metal sites from linear trinuclear clusters, SNNU-131 has better acetylene and carbon dioxide adsorption capacities of 88.5 and 49.9 cm³ g^–1 at 298 K and 1 bar. On the other hand, SNNU-132 with smaller triangular channels shows higher C₂H₂/CO₂ ideal adsorbed solution theory (IAST) selectivity values of 3.54–4.44, as well as a longer breakthrough interval time of 30 min g^–1 at 298 K and 1 bar. The preferred adsorption sites and density distributions of C₂H₂ and CO₂ molecules in these two metal–organic frameworks (MOFs) were further calculated by the Grand Canonical Monte Carlo (GCMC) simulations to understand their adsorption and separation performance.

A new two-dimensional coordination polymer (2D CP) {[Cd(Br-BDC)₂(DABCO)₂(DMF)]·0.5DMF}_n (BrCP-1; Br–H₂BDC = 2-bromo-1,4-benzenedicarboxylic acid and DABCO = 1,4-diazabicyclo[2.2.2]octane) was synthesized via the solvothermal reaction. Interestingly, the BrCP-1 exhibits strong luminescent property in pure aqueous media as well as in the solid state over an extended period when excited at 320 nm, emitting at 425 and 458 nm. The high luminescent property was explored for the rapid detection of tetracycline antibiotics and nitroaromatic (NAC) explosives in real-world environmental samples, including milk, river water, and soil samples. The UV–vis and fluorescence spectroscopic studies were performed to explain the resonance energy transfer and inner filter effect sensing mechanism accurately. Besides, the correction intensity (I_corr) for each analyte and correct quenching efficiency (QE_corr) were also evaluated. The density functional theory (DFT) experiment was also performed to evaluate the theoretical energy profile of respective tetracycline antibiotics and NACs, which established a proper photoinduced electron transfer (PET) mechanism.

Straight facets and sharp edges are among the most distinctive indicators of well-defined crystals and often reflect the polyhedral geometry and symmetry of the underlying close-packed, molecular structure. Curved morphologies are sometimes observed in biogenic crystals where templating or nonclassical crystallization processes (e.g., crystallization via amorphous states) occur. Here we report the formation and growth of copper-based metal–organic frameworks (MOFs) that crystallize in the hexagonal space group P622. The individual MOFs are homochiral and are formed from achiral compounds. The crystals begin as hexagonal-like structures, developing over time into complex flower-like structures having two decks joined in the center. Each deck layer has six well-defined petals with curved lateral surfaces. The growth mechanism shows initial straight petals that become progressively more curved with increased faceting. Remarkably, despite its multidomain appearance, the entire entity is a single crystal. The curved morphology is correlated to the crystallographic structure and the arrangement of nanosized channels within this structure. Crystal habits are typically considered to be inconsistent with curved morphologies. This work suggests that crystallographic explanations can support the development of such surfaces for low-density structures.

Our crystals have a two-sided, flower-like morphology with six curved petals on each side. Despite this complexity, the crystals are single. The morphological curvature was connected to the crystal structures by indexing the planes characterizing the petals during various growth stages and examining them relative to the solvent-crystal interfaces.

We developed an accurate machine learning interatomic potential for the thermosalient molecular crystal N-2-propylidene-4-hydroxybenzohydrazide. This crystal exhibits one of the largest mechanical responses during its thermosalient phase transition. Leveraging the speed of our developed potential, we performed Gibbs free energy calculations that successfully predict phase transitions in good agreement with experimental observations. Additionally, our model accurately captures the phenomenon of negative linear thermal expansion preceding the thermosalient phase transition. We show that the energy barrier exists at phase transition temperature and that this energy is purely elastic, elucidating the physical reasons for the thermosalient effect.

Effective combination of Al clusters with functional motif is a good way to expand the application of Al cluster materials. In this work, by introducing noble-metal ions with photothermal property into the assembly of aluminum clusters, four Al₈-based mixed metal complexes, {[Al₈Ag₂(OH)₈(NA)₁₆(CH₃CN)₂]·2SO₃CF₃}_n (Ag–Al₈, NA^– = nicotinic acid), {[(H₃O)₂Al₈Ag₃Cl₉(OH)₈(NA)₂(HNA)₁₄]·AgCl₄·Ag₂Cl₇·2SO₃CF₃}_n (AgCl-Al₈), {[Al₈Cu₄Br₃(OH)₈(NA)₁₆]·NA·HNA}_n (CuBr-Al₈-1) and {[Al₈Cu₄Br₂(OH)₈(NA)₁₆]·2NA}_n (CuBr-Al₈-2), were obtained. They are all constructed by the Al₈ ring cluster as the building unit and Ag/AgCl/CuBr-pyridine N as the linkers. Moreover, the Ag–Al₈ and AgCl-Al₈ show a photothermal conversion property under the irradiation of a 980 nm infrared laser. The temperatures of Ag–Al₈ and AgCl-Al₈ can respectively increase to 50 and 32 °C, and the photothermal conversion efficiency can reach 26.62 and 28.64%. Furthermore, the photothermal performance is reversible at least five irradiation cycles. This work first reports Al–Ag mixed metal frameworks with photothermal conversion performance based on aluminum metal clusters, enriching the family of Al cluster-based frameworks and expanding their application.

We report the selective area growth of N-polar GaN μ-platelets on graphene by metal–organic vapor-phase epitaxy. In a first step, GaN nanowires grown by selective molecular beam epitaxy on patterned graphene arrays on SiO₂ are used as nucleation seeds. The initial radius of the graphene patches results in different optical and crystalline quality of the GaN μ-platelets due to different coalescence mechanisms. The use of large graphene patches (250 nm) with significant number of nanowire seeds promotes the growth selectivity on patterned graphene at the expense of the structural quality (presence of voids, stacking faults, dislocations, and inversion domains). On the contrary, the use of smaller patches (65 nm) allows to grow μ-platelets from a very limited seed number (<3 nanowires) with a significantly reduced number of extended defects. These observations have been directly related to optical measurements by cathodoluminescence and high-resolution transmission electronic microscopy observations performed on the same μ-platelets for the different graphene patch radii (65, 90, 250 nm). The formation of defects is discussed and supported by nucleation, intra- and intercoalescence mechanisms.

The uranyl ion can form strong metal–ligand bonds with phosphonate groups, making it an excellent choice for constructing water-stable MOFs. However, reactions of uranyl ion and phosphonate ligands often occur too quickly, resulting in powders rather than single crystals. In this work, we employed a metalloligand strategy and synthesized four coordination polymers with layered structures, (UO₂)Fe(notpH)·0.5H₂O (1), (UO₂)Fe₂(notpH₂)₂·0.75H₂O (2), (UO₂)Co(notpH)(H₂O)·5H₂O (3), and (UO₂)₂Co₂(notpH)₂(H₂O)₂·7H₂O (4), by reacting metalloligands M^III(notpH₃) [M = Co, Fe; notpH₆ = 1,4,7-triazacyclononane-1,4,7-triyl-tris(methylenephosphonic acid)] with UO₂(OAc)₂ under hydrothermal conditions. By optimizing the synthesis conditions, we obtained pure phases of compounds 1, 3, and 4 and studied their stability in water. Compounds 1 and 3 were stable even in boiling water, whereas compound 4 converted to 3 after 2 days in boiling water. We also investigated the proton conductive properties of compounds 1 and 3.