Four-Step Spin Crossover in a New Cyano-Bridged Iron-Silver Coordination Polymer

Spin-crossover complexes with multistep transitions attract much attention due to their potential applications as multi-switches and for data storage. A four-step spin crossover is observed in the new iron(II)-based cyanometallic guest-free framework compound Fe(2-ethoxypyrazine)₂{Ag(CN)₂}₂ during the transition from the low-spin to the high-spin state. A reverse process occurs in three steps. Crystallographic studies reveal an associated stepwise evolution of the crystal structures. Multiple transitions in the reported complex originate from distinct Fe^II sites which exist due to the packing of the ligand with a bulky substituent.     

Bicomponent Cocatalyst Decoration on Flux-assisted CaTaO2N Single Crystals for Photocatalytic CO2 Reduction under Visible Light

Cubic-like CaTaO₂N photocatalysts with high crystallinity and uniform particle size were successfully prepared by the flux-assisted nitridation method. The growth of CaTaO₂N single crystals under different synthesis conditions was systematically investigated to understand the effects of the crystallinity and optical property on photocatalytic performance of CO₂ reduction. Moreover, the modification of CaTaO₂N single crystals with core-shell Ni−Ag bicomponent cocatalyst by two-step decoration process gave a 2.4 times higher amount of CO evolution than the deposition of sole Ag cocatalyst, because of the synergistic effects of bicomponent cocatalyst on the interfacial electron transfer and surface catalytic process. This study provides a valuable way to construct high-crystalline photocatalysts with effective bicomponent cocatalyst for visible-light-driven CO₂ reduction with H₂O.     

Ag(I)-Catalyzed/Acid-Mediated Cascade Cyclization of ortho-Alkynylaryl-1,3-dicarbonyls to Access Arylnaphthalenelactones and Furanonaphthol Libraries via Aryl-Disengagement

ortho-Alkynylarylketone derivatives were employed as key precursors for a one-pot synthesis of arylnaphthalenelactone and furanonaphthol libraries. In this work, we discovered a cost-effective protocol to prepare arylnaphthalenelactones in one-pot using inexpensive starting material, malonate ester, which was conveniently functionalized leading to a variety of structures. Moreover, we also found an unexpected oxy-dearylation reaction which could be used to synthesize furanonaphthol analogs. These novel methods could be applied to a broad range of substrates to give the corresponding products in up to 83% yield. Notably, these classes of compounds exhibited more significant inhibition against protein-tyrosine phosphatase 1B (PTP1B) enzyme than a standard compound, ursolic acid.     

The covalent functionalization of few-layered MoTe2 thin films with iodonium salts

Covalent functionalization of 2D materials provides a tailored approach towards tuning of their chemical, optical, and electronic properties making the search for new ways to graft small molecules important. Herein, the reaction with (3,5-bis(trifluoromethyl)phenyl)iodonium salt is revealed as an effective strategy for functionalization of MoTe₂ thin films. Upon decomposition of the salt, the generated radicals graft covalently as aryl-(CF₃)₂ groups at the surface of both metallic (1T’) and semiconducting (2H) polymorphs of MoTe₂. Remarkably, the reactivity of the salt is governed by the electronic structure of the given polymorph. While the functionalization of the metallic MoTe₂ occurs spontaneously, the semiconducting MoTe₂ requires activation by light. The reaction proceeds with the elimination of oxide from the original films yielding the functionalized products that remain protected in ambient conditions, presenting a viable solution to the ageing of MoTe₂ in air.     

基于抛光基材的热蒸镀铜箔生长高平整单层石墨烯薄膜

在石墨烯的化学气相沉积工艺中,铜箔是决定石墨烯薄膜质量的重要因素。传统铜箔由于制备工艺的限制,存在大量的缺陷,导致石墨烯薄膜的成核密度较高。本工作选用抛光铝板、抛光不锈钢板、微晶玻璃和SiO₂/Si作为基材,用热蒸镀法制备了不同粗糙度的铜箔,并详细讨论了以该系列铜箔生长高平整度石墨烯薄膜的条件及铜箔对石墨烯薄膜品质的影响。实验结果表明,铜箔以(111)取向为主,与基材分离后,表面具有纳米级平整度。在生长石墨烯后,从SiO₂/Si剥离的铜箔成核密度是4种基材中最小的。同时,从SiO₂/Si剥离的铜箔晶体结构变化最不明显,具有良好的结晶性,表面几乎不存在铜晶界缺陷。当压强为3 000 Pa,氢气和甲烷流速分别为300 mL/min和0.5 mL/min时,可以获得约1 mm横向尺寸的石墨烯单晶晶畴。     

New Palladium – ZrO2 Nano-Architectures from Thermal Transformation of UiO-66-NH2 for Carbonylative Suzuki and Hydrogenation Reactions

The new nanocomposites, Pd/C/ZrO₂, PdO/ZrO_2, and Pd/PdO/ZrO₂, were prepared by thermal conversion of Pd@UiO-66-Zr−NH₂ (MOF) in nitrogen or air atmosphere. The presence of Pd nanoparticles, uniformly distributed on the ZrO₂ or C/ZrO₂ matrix, was evidenced by transmission electron microscopy, scanning electron microscopy (SEM), Raman and X-ray Photoelectron Spectroscopy (XPS) methods. All pyrolysed composites retained the shape of the MOF template. They catalyze carbonylative Suzuki coupling under 1 atm CO with an efficiency significantly higher than the original Pd@UiO-66-Zr−NH₂. The most active PdO/ZrO₂ composite, formed benzophenone with TOF up to 1600 h⁻¹, while by using Pd@UiO-66-Zr−NH₂, much lower TOF values, 51–95 h⁻¹, were achieved. After the reaction, PdO/ZrO₂ was recovered with the same composition and catalytic activity. Very good results were also obtained in the transfer hydrogenation of benzophenones to alcohols with Pd/C/ZrO₂ and PdO/ZrO₂ catalysts under microwave irradiation.     

Properties of the Reactants and Their Interactions within and with the Enzyme Binding Cavity Determine Reaction Selectivities. The Case of Fe(II)/2-Oxoglutarate Dependent Enzymes

Fe(II)/2-oxoglutarate dependent dioxygenases (ODDs) share a double stranded beta helix (DSBH) fold and utilise a common reactive intermediate, ferryl species, to catalyse oxidative transformations of substrates. Despite the structural similarities, ODDs accept a variety of substrates and facilitate a wide range of reactions, that is hydroxylations, desaturations, (oxa)cyclisations and ring rearrangements. In this review we present and discuss the factors contributing to the observed (regio)selectivities of ODDs. They span from inherent properties of the reactants, that is, substrate molecule and iron cofactor, to the interactions between the substrate and the enzyme's binding cavity; the latter can counterbalance the effect of the former. Based on results of both experimental and computational studies dedicated to ODDs, we also line out the properties of the reactants which promote reaction outcomes other than the “default” hydroxylation. It turns out that the reaction selectivity depends on a delicate balance of interactions between the components of the investigated system.     

Benchmarking of Density Functionals for the Description of Optical Properties of Newly Synthesized π-Conjugated TADF Blue Emitters

Computational modeling of the optical characteristics of organic molecules with potential for thermally activated delayed fluorescence (TADF) may assist markedly the development of more efficient emitting materials for organic light-emitting diodes. Recent theoretical studies in this area employ mostly methods from density functional theory (DFT). In order to obtain accurate predictions within this approach, the choice of a proper functional is crucial. In the current study, we focus on testing the performance of a set of DFT functionals for estimation of the excitation and emission energy and the excited singlet-triplet energy gap of three newly synthesized compounds with capacity for TADF. The emitters are designed specifically to enable charge transfer by π-electron conjugation, at the same time possessing high-energy excited triplet states. The functionals chosen for testing are from various groups ranging from gradient-corrected through global hybrids to range-separated ones. The results show that the monitored optical properties are especially sensitive to how the long-range part of the exchange energy is treated within the functional. The accurate functional should also be able to provide well balanced distribution of the π-electrons among the molecular fragments. Global hybrids with moderate (less than 0.4) share of exact exchange (B3LYP, PBE0) and the meta-GGA HSE06 are outlined as the best performing methods for the systems under study. They can predict all important optical parameters correctly, both qualitatively and quantitatively.     

两个基于2,5-二甲氧基对苯二甲酸和咪唑衍生物的超分子钴配位聚合物的结构及光催化反应

本文以咪唑衍生物为配体,通过水热合成法与钴离子制备出两个配位聚合物:{[Co(DTA)(1,4-DIB)(H₂O)]·H₂O}_n(1)和[Co(DTA)(1,3-BMIB)]_n(2)(1,4-DIB=1,4-二(1H-咪唑-1-基)苯; 1,3-BMIB=1,3-二(4-甲基-1H-咪唑-1-基)苯;H₂DTA=2,5-二甲氧基对苯二甲酸)。利用X射线单晶衍射、粉末衍射、热失重、元素分析、红外光谱以及固体紫外-可见光谱等对两个配合物进行了表征。结构分析证实配合物1和2是通过二维结构堆积成的三维超分子化合物。粉末衍射测试则显示两个配合物在水中有很好的稳定性。固体紫外-可见光谱显示两个配合物属半导体材料,对紫外-可见光有很强的吸收作用。在光催化实验中,配合物1和2可加快亚甲基蓝的降解速度。     

Global existence and time decay of the non-cutoff Boltzmann equation with hard potential

This paper is concerned with the Cauchy problem on the Boltzmann equation without angular cutoff assumption for hard potential in the whole space. When the initial data is a small perturbation of a global Maxwellian, the global existence of solution to this problem is proved in unweighted Sobolev spaces $H^N\left({\mathbb{R}}_{x,v}^6\right)$ with $N\ge 2$. But if we want to obtain the optimal temporal decay estimates, we need to add the velocity weight function, in this case the global existence and the optimal temporal decay estimate of the Boltzmann equation are all established. Meanwhile, we further gain a more accurate energy estimate, which can guarantee the validity of the assumption in Chen et al. (0000).