Helical Coordination Polymers Based on Keggin-type POMs and N-donor Ligand

Two new 1D helical coordination polymers based on polyoxometalate were synthesized by self-assembly of Keggin-type POMs and copper salts in the presence of triangular N-heterocyclic derivatives or long-chain N-containing carboxylate ligand, that are, (H₃O)[{Cu(H₂tpim)₂}{SiMo₁₂O₄₀}] · 0.5H₂O [Htpim = 2,4,5-tri(4-pyridyl)-imidazole] ( 1 ) and [Cu₂(Hcpp)₃(cpp)(H₂O)][PMo₁₂O₄₀] · 2H₂O [Hcpp = 1-(4-cyanobenzyl)-3–2-yl)pyrazole] ( 2 ). Their structures were determined by single-crystal X-ray diffraction and further characterized by elemental analyses and TG analyses. Compounds 1 and 2 exhibit (1D→2D) interdigitated architectures assembled from 1D helical chains. In compound 1 , the achiral 2D interdigitated nets containing left- and right-handed helixes are further interdigitated with each other to form a 3D supramolecular framework. In compound 2 , adjacent 2D interdigitated layers with opposite chirality are further extended by supramolecular interactions into a 3D supramolecular network, in which non-coordinating Keggin-type POMs as guests are encapsulated.     

Facile Synthesis of MOF-derived Mn3O4@N-doped Carbon with Efficient Oxygen Reduction

Integration of MnO_x into the carbon matrix proves a viable strategy to improve the electrochemical performance of MnO_x materials. Mn₃O₄ nanoparticle-decorated N-doped carbon composites (Mn₃O₄@N-doped carbon) were facilely prepared from a non-porous eight-fold interpenetrated Zn^II-based MOF, which involves first synthesis of bimetallic Mn/Zn-MOF in one-pot reaction followed by direct pyrolysis at 1000 °C. In 0.1 m KOH solution, the optimal Mn₃O₄@N-doped carbon exhibits decent oxygen reduction activity with the onset potential (E_onset) of 0.94 V (vs. RHE) and half-wave potential (E_1/2) of 0.81 V (vs. RHE), excellent methanol tolerance as well as good durability.     

Dicyclohepta[ijkl,uvwx]rubicene with Two Pentagons and Two Heptagons as a Stable and Planar Non-benzenoid Nanographene

Polycyclic aromatic hydrocarbons with hexagons/pentagons or hexagons/heptagons have been intensively investigated in recent years, but those with simultaneous presence of hexagons, pentagons and heptagons remain rare. In this paper, we report dicyclohepta[ijkl,uvwx]rubicene ( DHR ), a non-benzenoid isomer of dibenzo[bc,kl]coronene with two pentagons and two heptagons. We developed an efficient and scalable synthetic method for DHR by using Scholl reaction and dehydrogenation. Crystal structure of DHR shows that the benzenoid rings, two pentagons and two heptagons are coplanar. The bond lengths analysis and the ICSS(1)zz and LOL-π calculations indicate that the incorporation of two formal azulene moieties has an effect on the conjugated structure. The π-electrons of benzenoid and pentagon rings are more delocalized. Cyclic voltammetry studies indicate that DHR shows multiple oxidation and reduction potentials. Interestingly, DHR exhibits unusual S₀ to S₂ absorption and abnormal anti-Kasha S₂ to S₀ emission. Moreover, crystals of DHR exhibit semiconducting behaviour with hole mobility up to 0.082 cm² V⁻¹ s⁻¹.     

Three-dimensional Octameric Assembly of Icosahedral M13 Units in [Au8Ag57(Dppp)4(C6H11S)32Cl2]Cl and its [Au8Ag55(Dppp)4(C6H11S)34][BPh4]2 Derivative

The high-dimensional (that is, three-dimensional (3D)) assembly of nanomaterials is an effective means of improving their properties; however, achieving this assembly at the atomic level remains challenging. Herein, we obtained a novel nanocluster, [Au₈Ag₅₇(Dppp)₄(C₆H₁₁S)₃₂C_l2]Cl (Dppp=1,3-bis(diphenylphosphino)propane) showing a 3D octameric assembly mode involving the kernel penetration of eight complete icosahedral Au@Ag₁₀Au₂ units for the first time. The atomically precise structure was determined by single-crystal X-ray diffraction, and further confirmed by thermogravimetric analysis, X-ray photoelectron spectroscopy, and electrospray ionization mass spectrometry measurements. Furthermore, ligand-induced transformation prompted the conversion of [Au₈Ag₅₇(Dppp)₄(C₆H₁₁S)₃₂Cl₂]Cl, with complete octameric fusion into [Au₈Ag₅₅(Dppp)₄(C₆H₁₁S)₃₄][BPh₄]₂, with incomplete octameric fusion. These observations will hopefully facilitate further research on the assembly of M₁₃ nanobuilding blocks.     

Two-Coordinate Copper(I)/NHC Complexes: Dual Emission Properties and Ultralong Room-Temperature Phosphorescence

As a kind of photoluminescent material, Cu^I complexes have many advantages such as adjustable emission, variable structures, and low cost, attracting attention in many fields. In this work, two novel two-coordinate Cu^I-N-heterocyclic carbene complexes were synthesized, and they exhibit unique dual emission properties, fluorescence and phosphorescence. The crystal structure, packing mode, and photophysical properties under different conditions were systematically studied, proving the emissive mechanism to be the locally excited state of the carbazole group. Based on this mechanism, ultralong room-temperature phosphorescence (RTP) with a lifetime of 140 ms is achieved by selective deuteration of the carbazole group. These results deepen the understanding of the luminescence mechanism and design strategy for two-coordinate Cu^I complexes, and prove their potential in applications as ultralong RTP materials.     

“Self-Lockable” Liquid Crystalline Diels–Alder Dynamic Network Actuators with Room Temperature Programmability and Solution Reprocessability

Novel main-chain liquid crystalline Diels—Alder dynamic networks (LCDANs) were prepared that exhibit unprecedented ease for actuator programming and reprocessing compared to existing liquid crystalline network (LCN) systems. Following cooling from 125 °C, LCDANs are deformed with aligned mesogens self-locked at room temperature by slowly formed Diels–Alder (DA) bonds, which allows for the formation of solid 3D actuators capable of reversible shape change, and strip walker and wheel-capable light-driven locomotion upon either thermally or optically induced order–disorder phase transition. Any actuator can readily be erased at 125 °C and reprogrammed into a new one under ambient conditions. Moreover, LCDANs can be processed directly from melt (for example, fiber drawing) and from solution (for example, casting tubular actuators), which cannot be achieved with LCNs using exchangeable covalent bonds. The combined attributes of LCDANs offer significant progress toward developing easily programmable/processable LCN actuators.     

高β相聚偏氟乙烯基复合体系的制备及压电性能

为了提高聚偏氟乙烯(PVDF)的压电性能,需要寻找有效的途径来提高PVDF的电活性相(β相)含量。 通过水热法成功合成了Ag、ZnO以及二者复合(Ag-ZnO)的3种类型纳米粒子,并与PVDF共混形成PVDF复合薄膜。 通过表征PVDF复合材料的形貌,结晶性能和压电性能,可以发现Ag-ZnO复合纳米粒子的协同作用可以有效提高PVDF的结晶性能和压电性能。 此外,通过单轴拉伸可以使得所有PVDF膜的β相含量得到进一步提高,其中拉伸后的PVDF/Ag-ZnO纳米颗粒(P-C)的β相物质的量分数最高,达到70.0％,最佳的压电系数(d₃₃)达到了31.0 pC/N。     

Co_2Si@C催化剂的合成及其加氢脱硫性能

采用微波法制备了Co_2Si@C催化剂并对其在加氢脱硫反应中的催化性能进行了研究.通过XRD、 XPS、 TEM和N_2-物理吸附表征分析Co_2Si@C催化剂的组成和结构. Co_2Si@C催化剂具有一致的介孔结构,高钴含量(21%)、高比表面积(116.6 m~2·g~(-1))和均匀分布的纳米粒子.由于硅原子对钴原子结构和参数的修饰、纳米粒子效应和高金属含量等因素, Co_2Si@C催化剂在温和的反应条件下(340℃和3.0 MPa)具有良好的加氢脱硫活性和对直接脱硫(DDS)反应途径的高选择性,产物联苯的选择性超过了60%.     

铂合金氧还原催化剂:合成、结构和性能

质子交换膜燃料电池是一种将燃料中的化学能直接转化为电能的装置,它具有转化效率高、能量密度高、低温启动、易于操作等优点,因而被认为是最具发展前景的新能源利用方式,在电动汽车、便携电源及分散式电站有着广泛应用.但是,目前质子交换膜燃料电池技术的发展面临着巨大挑战,主要问题包括高成本、低功率密度和低寿命.众所周知,质子交换膜燃料电池中的阴极氧还原反应在酸性条件下是一个复杂的四电子过程,动力学速度缓慢,限制了电池的最终性能.目前大量使用的阴极氧还原催化剂是细小的铂或铂合金纳米颗粒负载在碳载体上,其成本占燃料电池总成本的比例最大.制约燃料电池商业化发展的另一个重要问题是电池寿命低,其中氧还原催化剂的稳定性是决定电池寿命的主要因素.在这样的研究背景下,如何降低催化剂中铂的用量、提高催化剂活性和稳定性显得尤为重要,这也是近年来国内外学者研究的热点.在铂基合金催化剂中,通常采用过渡金属元素作为掺杂元素,由于原子半径不匹配(几何效应)以及电子结构不同(电子效应),合金催化剂表现出优于纯铂催化剂的催化性能.近几年,对于铂基合金催化剂的研究已取得重大进展,以合金组成和结构研究为基础,通过精确控制原子结构、调控表面电子状态以及制备工艺,获得了各种特殊形貌的催化剂,大大提高了催化活性.本文深入综述了近年来铂基合金氧还原催化剂制备、形貌和性能,特别关注了催化剂形貌和催化活性之间的关系.值得注意的是,具有有序原子排列的铂合金催化剂不仅在半电池中表现出优异活性,在实际质子交换膜燃料电池中也显示了很好的活性和稳定性.另一方面,碳载体的形貌及微观结构也对提高催化活性和稳定性起到决定性作用,通过化学手段加强金属纳米颗粒与碳载体之间的相互作用也是提高催化剂稳定性的重要途径.尽管铂基氧还原催化剂在近几年取得了重要进展,但在实际商业化过程中还存在诸多挑战,本文在综述进展的基础上,对铂基催化剂的发展提出了展望.首先,对于氧还原反应机理仍需要深入研究,采用更加精确的理论模型模拟氧还原动力学过程,以获得影响催化活性的关键因素.其次,提高催化剂在膜电极中的催化活性和利用率.目前,氧还原催化剂在半电池测试中性能优异,但是实际燃料电池操作条件下其性能远不能达到要求,这与膜电极、催化剂层及扩散层结构相关.因此,基于不同铂基催化剂的特性,合理设计膜电极组件的结构是将催化剂进行实际应用的基础.最后,催化剂的稳定性仍需进一步提高,尽管目前大部分催化剂在实验室半电池研究中表现了很好的稳定性,但在实际燃料电池中的稳定性研究还不足,而且对催化剂在膜电极中性能衰退机理的研究也非常有限.因此,对于铂基氧还原催化剂的研发仍需要国内外科研工作者不懈的努力.     

三氟乙酸酐(TFAA)促进的Stieglitz重排反应制备苯胺

本工作使用简单易得的三氟乙酸酐作为活化试剂,拓展了Stieglitz重排反应的底物适用范围,发展了一种通过C—C键断裂由苯乙基羟胺制备芳基伯胺的方法.该反应条件较为温和且对官能团具有较好的兼容性.机理研究表明,反应经历了活性三氟乙酸酯中间体的原位生成,并通过C—C和N—O键的断裂实现芳基迁移的过程.