New Approaches to N‑Heterocyclic-Carbene-Coordinated Iminoborane and Borenium Species

The synthesis, characterization, and reactivity of an iminoborane–N-heterocyclic carbene (NHC) adduct were described. The reaction of DmpNHB­(OEt)­Br [1; Dmp = 2,6-bis­(2,4,6-trimethylphenyl)­phenyl] with 2 equiv of 1,3-diimethyl-4,5-dimethylimidazol-2-ylidene (IMe4) resulted in the formation of an iminoborane–NHC complex 2. Both X-ray analysis and density functional theory calculations revealed the double-bond character of the BN bond in 2. Interestingly, compared with the corresponding Lewis-base-free iminoborane, 2 features a nitrogen atom with increased electron density, which could be attributed to coordination of the NHC. Similar to the isoelectronic species imine, this nitrogen center in 2 can be easily attacked by electrophiles. Indeed, the reaction of 2 with trimethylsilyl triflate (Me3SiOTf) afforded an NHC-stabilized borenium cation 3, representing a facile strategy to prepare cationic tricoordinate boron species

Uncoordinated Hexafluorosilicates in a Microporous Metal–Organic Framework Enabled C₂H₂/CO₂ Separation

Metal–organic frameworks (MOFs) represent a kind of low-energy physisorbent with modifiable pores and framework structures; however, a deep understanding of how these structural features influence properties is a prerequisite for the rational design and development of tailor-made materials for advanced applications. In this report, a MOF, [Ni2(TCPP-Ni)1/4(TPIM)2(COOH)­F]­[(Me2NH2)­SiF6]·xS (SDU-CP-1; S = solvent molecules, SDU = Shandong University, and CP = coordination polymer), assembled by tetrakis­(4-carboxyphenyl)­porphyrin (TCPP-Ni) and 2,4,5-tris­(4-pyridyl)­imidazole (TPIM) ligands as well as Ni2+ cations is reported. Interestingly, inorganic SiF62– anions do not serve as the pillars like precedents in the framework but are just counterions, which endows SDU-CP-1 with high uptake for C2H2 and adsorption selectivity (2.5–4.2) for C2H2/CO2 at room temperature, as certified by gas adsorption and separation experiments and grand canonical Monte Carlo calculation

Highly Water-Stable Zn₅ Cluster-Based Metal–Organic Framework for Efficient Gas Storage and Organic Dye Adsorption

The development of multi-functional materials as physical adsorbents for gas storage and dye adsorption is of utmost importance for ecological environment management. Ionic metal–organic frameworks (MOFs) with exchangeable counterions would easily be modified to enhance their performance. Herein, we report a novel {Zn5}-based MOF (SDU-CP-2) with the dimethylamine cation [(CH3)2NH2]+ in its crystal structure, which can be readily exchanged with Li+ ions and cationic dyes. Consequently, it exhibits high CO2 and C2H2 adsorption capacities as well as charge/size-selective adsorption of dye molecules. The adsorption of SDU-CP-2 toward cationic dyes was confirmed to be efficient in terms of recyclability and ion-exchange mechanisms. The column filler experiment and high water stability decisively supported its potential application in waste water treatment

Modulating CO₂ Adsorption in Metal–Organic Frameworks via Metal-Ion Doping

One novel metal–organic framework {[Ni₆(OH)₄­(BTB)_8/3­(H₂O)₆]·4H₂O·9DMF}_<i>n</i> (DMF = dimethylformamide) based on 1,3,5-benzenetribenzoic acid (H₃BTB) was successfully synthesized under basic condition at room temperature, featuring a unique twofold interpenetrated <b>pcu</b>-type net with [Ni₆(OH)₄­(COO)₈­(H₂O)₆] cluster as building block. Its gas-adsorption behaviors were investigated and modified by utilizing metal^II-doped procedure, which was certified to be a highly effective pathway in enhancing CO₂ uptake capacity

A new model predictive control approach integrating physical and data-driven modelling for improved energy performance of district heating substations

District heating (DH) substations play a crucial role in ensuring the efficient and effective distribution of thermal energy necessary to provide space heating for buildings. However, optimizing their operation for energy savings while still ensuring indoor comfort poses significant challenges due to the complex dynamics of building demand and the inertia of building envelopes. To address these challenges, this study introduces a novel model predictive control (MPC) approach that combines a reduced-order physical model with a machine learning-based data-driven model to jointly optimize the operation parameters of a DH substation. In this approach, a reduced-order physical model is first used to capture essential operational principles and energy behaviors of the DH substations and generate candidate solutions for the control of the DH substations. Then, a data-driven model is constructed by integrating a Long Short-Term Memory model and a Back-propagation Neural Network, leveraging historical operational data of the DH substation concerned. The data-driven model is further formulated into a data-driven MPC framework to identify optimal control solutions from all candidates provided by the physical model. To evaluate the proposed approach, a data-driven surrogate model is developed using real operational data. Comparative analysis against the original fuzzy rule-based control strategy and a pure data-driven strategy demonstrates a substantial reduction in heat consumption of 4.77% and 19.47%, respectively. Moreover, compared with using a reduced-order physical model alone, this approach achieves additional benefits in reducing the energy consumption of the DH substation and minimizing indoor temperature fluctuations within the end-users

Prediction of a Kinetic Pathway for Fabricating the Narrowest Zigzag Graphene Nanoribbons on Cu(111)

The narrowest zigzag graphene nanoribbons (nZGNRs) consisting of linearly fused benzene rings have distinctly superior electronic and spintronic properties; yet, to date, fabrication of nZGNRs via bottom-up self-assembly remains a daunting challenge. Here, based on first-principles calculations, we propose a kinetic pathway for growing nZGNRs on Cu(111) using 1,4-dibromo-2,5-bis­(bromomethyl)­benzene precursors. We show that such a precursor molecule can readily adsorb on Cu(111), accompanied by easy detachment of the four Br substituents. As building blocks for the formation of the nZGNRs, the resulting C8H6 radicals have high diffusional and rotational mobilities on the substrate. Two such radicals can fuse into an nZGNR-like dimer via covalent bond formation by overcoming a kinetic barrier of ∼1.00 eV, with the unsaturated C atoms properly located to allow additional C8H6 radicals to join and elongate the nZGNR. We further examine possible competing byproducts and find that the yields of nZGNRs can be enhanced with proper choices of the substrates. As a comparative study, the precursor molecule of 1,4-bis­(bromomethyl)­benzene has also been investigated and found to be less desirable in forming the nZGNRs. These findings provide a highly appealing route toward the fabrication of nZGNRs for potential applications in nanoelectronics and spintronics

High-Rate Solid Polymer Electrolyte Based Flexible All-Solid-State Lithium Metal Batteries

A flexible poly­(vinylidene fluoride)-polyetherimide@poly­(ethylene glycol) (PVDF-PEI@PEG) solid composite polymer electrolyte is prepared by an in situ thermal curing approach. The homogeneous PVDF-PEI composite porous membrane with an optimized PVDF and PEI weight ratio increases the amorphous phase, while the fast lithium ion transport channels are formed through the filled PEG electrolytes. The optimized polymer electrolyte exhibits high ionic conductivity of 2.36 × 10–4 S cm–1 at 60 °C and lithium ion transference number of 0.578 as well as excellent electrochemical stability window of 5.5 V. Moreover, the superior stability toward lithium metal anode enables over 3600 h cycling of the Li//Li symmetric cell at 0.1 mA cm–2. In particular, the LiFePO4//Li battery delivers high specific capacities of 132.4 and 111.5 mAh g–1 with a retention of 86.6% and 85.9% after 200 cycles at 2 C and 100 cycles at 3 C rate under 60 °C, respectively, demonstrating the feasibility as an energy storage device with high rate capability

Coexistence of Superconductivity and Nontrivial Band Topology in Monolayered Cobalt Pnictides on SrTiO₃

As an intrinsically layered material, FeSe has been extensively explored for potentially revealing the underlying mechanisms of high transition temperature (high-Tc) superconductivity and realizing topological superconductivity and Majorana zero modes. Here we use first-principles approaches to identify that the cobalt pnictides of CoX (X = As, Sb, Bi), none of which is a layered material in bulk form. Nevertheless, all can be stabilized as monolayered systems either in freestanding form or supported on the SrTiO3(001) substrate. We further show that each of the cobalt pnictides may potentially harbor high-Tc superconductivity beyond the Cu- and Fe-based superconducting families, and the underlying mechanism is inherently tied to their isovalency nature with the FeSe monolayer. Most strikingly, each of the monolayered CoX’s on SrTiO3 is shown to be topologically nontrivial, and our findings provide promising new platforms for realizing topological superconductors in the two-dimensional limit

Ultrastrong Alkali-Resisting Lanthanide-Zeolites Assembled by [Ln₆₀] Nanocages

Zeolites, as one of the most important porous materials, are most widely utilized in sorbents, catalysis, and ion-exchange fields. However, the multi-functional lanthanide-zeolites constructed exclusively by lanthanide ions and oxygen linkers are to our knowledge unknown hitherto. Herein, we, for the first time, report the unique structure and multifunctions of lanthanide zeolites (<b>1·Gd</b>, <b>1·Tb</b>, <b>1·Dy</b>), featuring 60 nuclear [Ln₆₀] nanocages as building blocks and ultrastrong alkali-resisting. These compounds possess extremely high stability and still retain single crystallinity after treatment in boiling water, 0.1 M HCl, and 20 M NaOH aqueous solutions. Magnetic studies revealed <b>1·Gd</b> has large magnetocaloric effect with −Δ<i>S</i>_m^max = 66.5 J kg^–1 K^–1, falling among the largest values known to date. Importantly, these lanthanide-zeolites themselves can efficiently catalyze the cycloaddition of CO₂ with epoxides under mild conditions. Our finding extends the conventional zeolites to lanthanide counterparts, opening a new space for seeking novel and/or multifunctional zeolites

Anisotropic Dzyaloshinskii–Moriya Interaction and Topological Magnetism in Two-Dimensional Magnets Protected by <i>P</i>4̅<i>m</i>2 Crystal Symmetry

As a fundamental magnetic parameter, Dzyaloshinskii–Moriya interaction (DMI), has gained a great deal of attention in the last two decades due to its critical role in formation of magnetic skyrmions. Recent discoveries of two-dimensional (2D) van der Waals (vdW) magnets has also gained a great deal of attention due to appealing physical properties, such as gate tunability, flexibility, and miniaturization. Intensive studies have shown that isotropic DMI stabilizes ferromagnetic (FM) topological spin textures in 2D magnets or their corresponding heterostructures. However, the investigation of anisotropic DMI and antiferromagnetic (AFM) topological spin configurations remains elusive. Here, we propose and demonstrate a family of 2D magnets with P4m2 symmetry-protected anisotropic DMI. More interestingly, various topological spin configurations, including FM/AFM antiskyrmion and AFM vortex–antivortex pair, emerge in this family. These results give a general method to design anisotropic DMI and pave the way toward topological magnetism in 2D materials using crystal symmetry