Building Units Research Articles

Growth Mediated Disassembly of Cucurbit[8]uril Cross‐linked Static Cubic Self‐assembly of Silver Nanoparticles

AbstractStatic self‐assembly resides in thermodynamically stable global minima of the energy landscape, whereas dynamic self‐assembly occupies local minima of the energy profile and remains in the ordered state for a limited time via dissipation of energy to surroundings. This makes the spatiotemporal control over the assembly and disassembly mechanism easily controllable in the case of dynamic self‐assembly. However, due to the higher thermal stability of static self‐assembly, it is very challenging to perform reverse engineering on these types of systems. Herein we report growth reaction‐based reversal of static silver cubes obtained via cucurbit[8]uril (CB[8]) crosslinked self‐assembly of silver nanoparticles (AgNP). The AgNP building units with variable CB[8] surface coverage have been used as seeds onto which deposition of gold via growth reaction has been performed. The disassembly of supracube structure has been controlled by the formation of [AuCl4]−–CB[8] complex and successive reduction of [AuCl4]− to Au0 on the surface of the seed. The resulting monodispersed isotropic nanoparticles, formed from the CB[8] based cubic self‐assembly after growth, exhibit Au−Ag bimetallic nature. Quenching of the fluorogenic response from the hydrophobic dye coumarin‐7, added after growth, suggests direct interaction with the metallic nanoparticle surface after disassembly and thereby confirms successful growth reaction mediated reversal of self‐assembly.

A Multimetal Approach for the Reticulation of Iridium into Metal-Organic Framework Building Units.

Noble metal elements are ubiquitous in our everyday life, from medical applications to electronic devices and synthetic chemistry. Iridium is one of the least abundant elements, and despite its scarcity, it remains essential for efficient and active catalytic processes. Consequently, the development of heterogeneous catalysts with the presence of active iridium sites is of enormous interest as it leads to the improvement of their recyclability and reusability. Here, we demonstrate a strategy to incorporate iridium atoms into metal-organic frameworks (MOFs), as part of their secondary building units (SBUs), resulting in robust and reusable materials with heterogeneous photocatalytic activity.

A new three-dimensional barium(II) coordination polymer constructed from N,N'-bis(glycinyl)pyromellitic diimide: microwave-assisted synthesis, structure, Hirshfeld surface analysis and properties.

A new three-dimensional (3D) coordination polymer, namely, poly[diaqua[μ5-2,2'-(1,3,5,7-tetraoxo-1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole-2,6-diyl)diacetato]barium(II)], [Ba(C14H6N2O8)(H2O)2]n, (I), has been synthesized by the microwave-irradiated reaction of Ba(NO3)2 with N,N'-bis(glycinyl)pyromellitic diimide {BGPD, namely, 2,2'-(1,3,5,7-tetraoxo-1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole-2,6-diyl)diacetatic acid, H2L}. The title compound was structurally characterized by single-crystal X-ray diffraction analysis and powder X-ray diffraction analysis, as well as IR spectroscopy. In the crystal structure of (I), the BaII ion is nine-coordinated by six carboxylate O atoms from five symmetry-related L2- dianions and one imide O atom, as well as two water O atoms. The coordination geometry of the central BaII ion can be described as a spherical capped square antiprism. One carboxylate group of the ligand serves as a μ3-bridge linking the BaII cations into a one-dimensional polynuclear secondary building unit (SBU). Another carboxylate group of the ligand acts as a μ2-bridge connecting the 1D SBUs, thereby forming a two-dimensional (2D) SBU. The resulting 2D SBUs are extended into a 3D framework via the pyromellitic diimide moiety of the ligand as a spacer. The 3D Ba framework can be simplified as a 5-connected hexagonal boron nitride net (bnn) topology. The intermolecular interactions in the 3D framework were further investigated by Hirshfeld surface analysis and the results show that the prominent interactions are H...O (45.1%), Ba...O (11.1%) and C...H (11.1%), as well as H...H (11.1%) contacts. The thermal stability, photoluminescence properties and UV-Vis absorption spectra of (I) were also investigated. The coordination polymer exhibits a fluorescence emission with a quantum yield of 0.071 and high thermal stability.

Efficient cascade reactions involving esterification, hydrogen transfer, and lactonization for biomass conversion using MOF/Metal oxide composites as heterogeneous catalysts

Development of heterogeneous catalysts with both Brønsted and Lewis acid properties has proved to be promising and useful because they offer an efficient way to cascade reactions. In this study, we present the synthesis pathway and efficacy evaluation of new composites which combined by sulfonic acid functional group modified TiO2 and MIL-101, analyzing their structure-performance correlation as heterogeneous catalysts in cascade reactions involving esterification, hydrogen transfer, and lactonization. These composites possess an open porous structure (MOF and porous TiO2), as well as active sites including Lewis acid (unsaturated coordination metal), Lewis base (Ti-OH), and Brønsted acid (-SO3H). The role of these active sites and the synergies between them were investigated through the esterification of levulinic acid and the direct synthesis of γ-valerolactone from levulinic acid and furfural under cascade reactions. The composites exhibit a 100% ethyl levulinate (EL) yield at 120°C for 6 hours, with γ-valerolactone yields reaching up to 94.5% (160 °C, 9 h) and 89.5% (160 °C, 16 h) from levulinic acid and furfural, respectively. This synergistic effect of Lewis acid/base and Brønsted acid ensures efficient esterification. The presence of a sulfonic acid group promotes the lactonization reaction, while the Meerwein-Ponndorf-Verley reduction is facilitated by the dual Cr sites located adjacent to each other in the secondary building unit of MIL-101(Cr). Moreover, the double-porous structure of porous TiO2 and MIL-101(Cr) effectively guarantees the efficient mass transfer of reactants and intermediates, leading to enhanced synergistic effects that promote more efficient reaction conversion.

2D coordination polymers of cadmium(II) and zinc(II) derived from N,N'-bis(glycinyl)pyromellitic diimide: microwave-assisted synthesis, structures, spectroscopic properties and influence of metal-ion size.

Two new two-dimensional (2D) coordination polymers (CPs), namely, poly[diaqua[μ4-2,2'-(1,3,5,7-tetraoxo-1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole-2,6-diyl)diacetato-κ4O:O':O'':O''']cadmium(II)], [Cd(C14H6N2O8)(H2O)2]n (1), and poly[[tetraaqua[μ4-2,2'-(1,3,5,7-tetraoxo-1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole-2,6-diyl)diacetato-κ4O:O':O'':O'''][μ2-2,2'-(1,3,5,7-tetraoxo-1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole-2,6-diyl)diacetato-κ2O:O']dizinc(II)] dihydrate], {[Zn(C14H6N2O8(H2O)2]·H2O}n (2), have been synthesized by the microwave-irradiated reaction of Cd(CH3COO)2·2H2O and Zn(CH3COO)2·2H2O, respectively, with N,N'-bis(glycinyl)pyromellitic diimide {BGPD, namely, 2,2'-(1,3,5,7-tetraoxo-1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole-2,6-diyl)diacetic acid, H2L}. In the crystal structure of 1, the CdII ion is six-coordinated by four carboxylate O atoms from four symmetry-related L2- dianions and two coordinated water molecules, furnishing an octahedral coordination geometry. The bridging L2- dianion links four symmetry-related CdII cations into a 2D layer-like structure with a 3,4-connected bex topology. In the crystal structure of 2, the ZnII ion is five-coordinated by three carboxylate O atoms from three different L2- dianions and two coordination water molecules, furnishing a trigonal bipyramidal coordination geometry. Two crystallographically independent ligands serve as μ4- and μ2-bridges, respectively, to connect the ZnII ions, thereby forming a 2D layer with a 3,3-connected hcb topology. Crystal structure analysis reveals the presence of n→π* interactions between two carbonyl groups of the pyromellitic diimide moieties in 1 and 2. CP 1 exhibits an enhanced fluorescence emission compared with free H2L. The framework of 2 decomposes from 720 K, indicating its high thermal stability. A comparative analysis of a series of structures based on the BGPD ligand indicates that the metal-ion size has a great influence on the connection modes of the metal ions due to different steric effects, which, in turn, affects the structures of the SBUs (secondary building units) and frameworks.

Spiral Substructures of Nanowires Determined by the Universal Building Unit (Tetrablock)

Spiral Substructures of Nanowires Determined by the Universal Building Unit (Tetrablock)

Harnessing the clean energy: Phosphorus-alkynyl covalent organic frameworks for photocatalytic hydrogen production

Given the diminishing reserves of fossil fuels, the development of renewable alternative energy sources is of global importance. Photocatalytic hydrogen (H2) evolution stands out as a promising and cost-effective method to harness sunlight for producing carbon-free H2 fuel. Recently, two-dimensional (2D) covalent organic frameworks (COFs) have garnered considerable research interest in photocatalysis on account of their exceptional surface area and predictable assembly of diverse molecules with adjustable electronic properties. Herein, six 2D COFs are constructed by topologically assembling phosphorus-alkynyl functional moieties and benzene-based building units, including benzene (COF-1), triazine (COF-2), heptazine (COF-3), triphenyl-benzene (COF-4), triphenyl-triazine (COF-5), and triphenyl-heptazine (COF-6), employing first-principles calculations. Our computational results illustrate that the variation of benzene-based building units significantly regulates the electronic structures of COFs, all of which possess semiconductor properties with tunable bandgaps spanning from 1.56 to 2.56 eV. Of particular importance, COF-1, COF-2, COF-4, COF-5, and COF-6 can spontaneously stimulate the hydrogen evolution reaction (HER) under their own light-induced bias without the need for sacrificial agents and co-catalysts. Among them, COF-4 and COF-5 show the best HER activity without light-induced bias, with ΔG values of 0.02 and −0.01 eV, respectively, whose excellent photocatalytic performance can be ascribed to their appropriate electronic band structures, pronounced optical absorption, and low work functions. This finding offers profound insights for exploring other highly efficient HER photocatalysts.

Advancing Single-Particle Analysis in Synthetic Chemical Systems: A Forward-Looking Discussion.

Single-particle analysis (SPA) is a fundamental method of cryo-electron microscopy developed to resolve the structures of biological macromolecules. This method has seen significant success in structural biology, yet its potential applications in synthetic chemical systems remain underexplored. In this perspective article, SPA and associated electron microscopy techniques are first briefly introduced. It is then proposed that SPA is well-suited for structural analysis of chemical systems where discrete, identical macromolecules can be readily obtained. Applicable systems include various clusters such as coinage metal clusters, metal-oxo/sulfur clusters, metal-organic clusters, and supramolecular compounds like coordination cages and metallo-supramolecular cages. When high-quality large single crystals are unattainable, SPA provides an alternative method for determining their structures. Beyond these end products, it is suggested that SPA can be instrumental in studying synthetic intermediates of materials with specific building units, such as metal-organic frameworks and zeolites. Given that various intermediates coexist in the reaction system, a purification step is necessary before conducting SPA, which can be facilitated by soft-landing electrospray ionization mass spectrometry.

Enhancing arsenate removal through interpretable machine learning guiding the modular design of metal–organic frameworks

The modular design of metal–organic frameworks (MOFs) for enhancing arsenate (As(V)) adsorption remains a challenge. We have developed twelve interpretable machine learning prediction models by integrating six decision tree-based algorithms with two molecular fingerprints, Morgan and MACCS. The optimal XGBoost-Morgan model, with its high determination coefficient of 0.97 and low root mean square error of 11.78, not only demonstrates excellent prediction and generalization capabilities in As(V) adsorption capacity, but also validates the feasibility of modeling concepts by feature engineering adopted in this work. Our comprehensive model interpretation initiates with the molecular fragment composition of the organic linkers, the secondary building units, and the topological nets, that constitute MOFs, and structure parameters. It culminates in the proposal of a reticular chemistry design scheme specifically tailored for the adsorption of As(V) by MOFs. Furthermore, it delineates the optimal environmental conditions conducive to effective As(V) adsorption. We anticipate that our MOF design strategy will be extensively applicable to the target removal of pollutants.

Organic template-free synthesis of CHA zeolite by hydrothermal conversion of magadiite with the assistance of seeds and an investigation of crystallization mechanism

This study aims to explore the process of pure CHA zeolite production by a hydrothermal magadiite transformation method, with the chemical formulation of 36 NaOH: 40 SiO2: Al2O3: 400H2O, running for 7 h at 80 °C with 12 wt% seeds. Considering various synthesis factors such as NaOH/SiO2, temperature, and seeds dosage etc., XRD, SEM, FT-IR, Solid-state MAS NMR and ESI-MS were applied to investigated to discuss the transformation behavior and mechanism in both solid and liquid phase. The results indicated that the changes of secondary building units had a formation sequence progresses from 6 R s to D6Rs, and oligomers in liquid phases would take part in the formation of CHA framework. In conclusion, the study demonstrates a novel pathway for the highly efficient and green synthesis of CHA zeolite via seed-assisted hydrothermal conversion of magadiite.

Recognition and order of multiple sidechains by metal-organic framework enhances the separation of hexane isomers.

Porous materials perform molecular sorting, separation and transformation by interaction between their framework structures and the substrates. Proteins also interact with molecules to effect chemical transformations, but rely on the precise sequence of the amino acid building units along a common polypeptide backbone to maximise their performance. Design strategies that positionally order sidechains over a defined porous framework to diversify the internal surface chemistry would enhance control of substrate processing. Here we show that different sidechains can be ordered over a metal-organic framework through recognition of their distinct chemistries during synthesis. The sidechains are recognised because each one forces the common building unit that defines the backbone of the framework into a different conformation in order to form the extended structure. The resulting sidechain ordering affords hexane isomer separation performance superior to that of the same framework decorated only with sidechains of a single kind. The separated molecules adopt distinct arrangements within the resulting modified pore geometry, reflecting their strongly differentiated environments precisely created by the ordered sidechains. The development of frameworks that recognise andorder multiple sidechain functionality by conformational control offers tailoring of the internal surfaces within families of porous materials to direct interactions at the molecular level.

GFP Chromophore Integrated Conjugated Microporous Polymers toward Bioinspired Photocatalytic CO2 Reduction to CO.

The development of highly active, durable, and low-cost metal-free catalysts for the photocatalytic CO2 reduction reaction (CO2RR) is an efficient and environmentally friendly solution to address significant problems like global warming and high energy demand. In the present study, we have demonstrated the design and synthesis of a donor-acceptor based conjugated microporous polymer (CMP), TPA-GFP, by integrating an electron donor, tris(4-ethynylphenyl)amine (TPA), with a green fluorescent protein chromophore analogue (Z)-4-(2-hydroxy-3,5-diiodobenzylidene)-1-(4-iodophenyl)-2-methyl-1H-imidazol-5(4H)-one (o-HBDI-I3) (GFP). In comparison to nondonor 1,3,5-triethynylbenzene (TEB) based TEB-GFP CMP, photocatalytic CO2 reduction using donor-acceptor based TPA-GFP CMP displays a 3-fold increment of CO production yield with a maximum CO yield of 1666 μmol g-1 at 12 h. Further, the CO selectivity increases significantly from a mere 54% in TEB-GFP to an impressive 95% in TPA-GFP. The impressive CO2 reduction efficiency and selectivity for TPA-GFP can be attributed to the efficient light-harvesting capability and facile charge separation and migration through donor-acceptor building units of the CMP. The mechanistic aspect of the photocatalytic CO2 reduction process is explored using in situ DRIFTS and DFT calculation, and a plausible photocatalytic mechanism is proposed.

Promising Functional Structural Building Unit Trisulfimide (SO2N)33– and Its Contributions to Second Harmonic Generation and Birefringence

Promising Functional Structural Building Unit Trisulfimide (SO₂N)₃^3– and Its Contributions to Second Harmonic Generation and Birefringence

O-arylation reaction over lanthanide metal–organic framework: Synthesis, structure and catalytic reaction

Two novel lanthanide based two-dimensional metal-organic framework (MOF) compounds [Tb(NDC)(NO3)(DMA)2]n (MOF-1) and [Ho(NDC)(NO3)(DMA)2]n (MOF-2) [H2NDC=2,6-naphthalenedicarboxylic acid and DMA=N,N-dimethylacetamide] have been synthesized following solvothermal route and structurally characterized. Structural analysis reveals that both the compounds are crystallized in the orthorhombic crystal system with space group Pbca. MOFs feature a “paddle-wheel” (PW) type core building units which are constructed via carboxylato oxygen coordination with lanthanide atoms. 2D lanthanide based MOFs consist of paddle-wheel building block are rare in the literature. MOF-1 and MOF-2 possess an octa-coordinated metal center. Apart from carboxylato groups, oxygen atoms of DMA and NO3− ions are also coordinated to metal centers. Paddle-wheel cores are interconnected to each other to give rise to layered network structure in both the cases. 2D layers are propagated parallel to bc plane and layers are stacked one upon another along the crystallographic a axis. Notably, both MOF-1 and MOF-2 are capable to catalyze O-arylation reaction efficiently under heterogeneous medium. However, amongst them, catalytic efficacy of MOF-1 towards O-arylation reaction is found to be better than that of MOF-2.

Leveraging multi-zone building data with machine learning-based models and genetic algorithms to optimize air handling units

Optimizing air handling units (AHUs) in multi-zone buildings presents significant challenges. As buildings become more complex, the demand for tailored temperature control across various zones becomes paramount. This study leverages multi-zone building data with machine learning-based models and optimization techniques to optimize AHUs by specifically integrating deep neural network (DNN) modeling, clustering analysis, and a genetic algorithm (GA). We developed 18 models to predict AHU supply air temperature (Tsa) and 2 models to predict chiller power consumption (P) using DNN. Clustering analysis was applied to the return air temperature (Tra) of each AHU, serving as initial conditions for the GA. The clustering analysis provided insights into the AHU operational behavior, enhancing the optimization process precision. The GA's objective function maintained the AHUs' Tsa and minimized P by adjusting parameters such as valve openings, fan frequencies, chilled water supply temperature, and cooling water flowrate. The results indicated that DNN models demonstrated high predictive accuracy, with 16 models showing an R2 higher than 0.96. The results suggested that AHU411 requires increased capacity during high Tra condition, while AHU212 needs an enhanced model with more diverse training data or the incorporation of additional influencing factors. Validation revealed that this approach improved temperature maintenance across zones, with 96 % of the data falling within demand temperature range (Tset), and achieving Tset required 41 % higher power input.

Covalent Organic Frameworks for Photocatalytic Reduction of Carbon Dioxide: A Review.

Covalent organic frameworks (COFs) are crystalline networks with extended backbones cross-linked by covalent bonds. Due to the semiconductive properties and variable metal coordinating sites, along with the rapid development in linkage chemistry, the utilization of COFs in photocatalytic CO2RR has attracted many scientists' interests. In this Review, we summarize the latest research progress on variable COFs for photocatalytic CO2 reduction. In the first part, we present the development of COF linkages that have been used in CO2RR, and we discuss four mechanisms including COFs as intrinsic photocatalysts, COFs with photosensitive motifs as photocatalysts, metalated COF photocatalysts, and COFs with semiconductors as heterojunction photocatalysts. Then, we summarize the principles of structural designs including functional building units and stacking mode exchange. Finally, the outlook and challenges have been provided. This Review is intended to give some guidance on the design and synthesis of diverse COFs with different linkages, various structures, and divergent stacking modes for the efficient photoreduction of CO2.

Self‐Calibration Temperature Sensing and Color Tunable Emission in a Bimetallic Lanthanide Metal–Organic Framework

ABSTRACTTemperature in various scientific and industrial applications requires accurate detection and measurement. Herein, a range of novel isostructural lanthanide‐based metal–organic frameworks (Ln‐MOFs), [EuxTb2−x(3,5‐pdc)3(phen)2(H2O)2]n (x = 0, Tb‐MOF; x = 2, Eu‐MOF; x = 0.002, 0.010, 0.020, 0.040, 0.080, EuxTb2−x‐MOF), were solvothermally synthesized using 3,5‐pyridinedicarboxylic acid (3,5‐H2pdc) and 1,10‐phenanthroline (phen) as ligands. Based on binuclear second building units, Ln‐MOFs exhibited 2D layered structure with sql topology. The luminescent properties of series Ln‐MOFs show systematic tuning shifted from green to red by adjusting the ratio of Eu3+ to Tb3+. The temperature sensing experiments showed that Eu0.020Tb1.980‐MOF exhibited self‐calibration temperature response in a range of 293–413 K, achieving maximum relative sensitivity (Sr) 2.46%·K−1 at 413 K, outscoring many state‐of‐the‐art temperature sensors reported in literature. This study poses great promise of the newly designed Eu0.020Tb1.980‐MOF for the ultra‐sensitive temperature sensing in diverse and large‐scale applications.

CdInO(BO3): An oxyborate birefringent material explored from d10 metal compounds

Birefringent crystals are particularly important in optical communication and laser industries. Herein, we report the synthesis, structures, optical properties, and theoretical analyses of an oxyborate birefringence material CdInO(BO3). It has an interesting sandwich-like basic building unit (BBU) constructed by [CdO4]6− chains and [InO4]5− chains. CdInO(BO3) possesses an experimental band gap of 3.65 eV and an ultraviolet (UV) cut-off edge about 295 nm. Moreover, it exhibits a large birefringence (0.136@1064 nm), which mainly originates from the parallel arrangement of the isolated [BO3] groups. This discovery indicates that CdInO(BO3) can be a promising birefringent material.

Narrowband clusteroluminescence with 100% quantum yield enabled by through-space conjugation of asymmetric conformation

Different from traditional organic luminescent materials based on covalent delocalization, clusteroluminescence from nonconjugated luminogens relies on noncovalent through-space conjugation of electrons. However, such spatial electron delocalization is usually weak, resulting in low luminescent efficiency and board emission peak due to multiple vibrational energy levels. Herein, several nonconjugated luminogens are constructed by employing biphenyl as the building unit to reveal the structure-property relationship and solve current challenges. The intramolecular through-space conjugation can be gradually strengthened by introducing building units and stabilized by rigid molecular skeleton and multiple intermolecular interactions. Surprisingly, narrowband clusteroluminescence with full width at half-maximum of 40 nm and 100% efficiency is successfully achieved via an asymmetric conformation, exhibiting comparable performance to the traditional conjugated luminogens. This work realizes highly efficient and narrowband clusteroluminescence from nonconjugated luminogens and highlights the essential role of structural conformation in manipulating the photophysical properties of unconventional luminescent materials.

Blast Performance of Polyurea-Coated Modular Structure Composed of Fiber-Reinforced Polymer and Foam Sandwich Panels

Lightweight modular structures have become a requirement in today’s world, especially for areas that are prone to occurrence of extreme events, such as earthquakes and blasts, and are situated in difficult terrains with challenging accessibility. Sandwiched composites can be one of the most suitable building units for construction of these structures due to their engineered mechanical and physical properties. Therefore, in this numerical study, performance assessment of a sandwich modular structure in the shape of a truncated cylinder is conducted under blast load. The sandwich modular structure is composed of flat and curved carbon fiber-reinforced polymer (CFRP) and extruded polystyrene (XPS) foam sandwich panels. A three-dimensional (3D) finite element (FE) model of the sandwich modular structure is developed considering the orthotropic behavior of CFRP facesheets and the crushing foam behavior is accounted for the XPS foam core in the FE modeling. The damage assessment in the CFRP facesheet is performed using Hashin’s damage criterion. Furthermore, the effect of polyurea with varying thicknesses on the blast-resistance of the structure is investigated. The polyurea is modeled as hyperelastic material using the Mooney-Rivlin model. The influence of polyurea positioning is studied when (a) applied externally to flat and curved walls of the structure directly exposed to the blast and (b) applied internally to flat and curved walls of the structure opposite to the exposure of the blast (rear face). It is observed that the flat walls of the structure are more vulnerable to the blast load than the curved walls of the structure. Moreover, a quadratic and linear reduction in the deflection of flat and curved walls with increasing thickness of polyurea coating is obtained, respectively. In addition, with increasing thickness of the additional polyurea coating, a logarithmic reduction in the kinetic energy of the sandwich modular structure is reported.