[B30]−: A Quasiplanar Chiral Boron Cluster Li, Wei-Li; Zhao, Ya-Fan; Hu, Han-Shi ...
Angewandte Chemie (International ed.),
May 26, 2014, Letnik:
53, Številka:
22
Journal Article
Recenzirano
Chirality is vital in chemistry. Its importance in atomic clusters has been recognized since the discovery of the first chiral fullerene, the D2 symmetric C76.1 A number of gold clusters have been ...found to be chiral,2 raising the possibility to use them as asymmetric catalysts. The discovery of clusters with enantiomeric structures is essential to design new chiral materials with tailored chemical and physical properties.3 Herein we report the first inherently chiral boron cluster of B30− in a joint photoelectron spectroscopy and theoretical study. The most stable structure of B30− is found to be quasiplanar with a hexagonal hole. Interestingly, a pair of enantiomers arising from different positions of the hexagonal hole are found to be degenerate in our global minimum searches and both should co‐exist experimentally because they have identical electronic structures and give rise to identical simulated photoelectron spectra.
Holey chiral: The B30− cluster was characterized by photoelectron spectroscopy and ab initio calculations. A pair of planar structures with a hexagonal hole at different positions are found to be degenerate with identical electronic structures. These two isomers are enantiomers, suggesting that B30− is the first chiral boron cluster.
Lithium metal is considered a “Holy Grail” of anode materials for high‐energy‐density batteries. However, both dendritic lithium deposition and infinity dimension change during long‐term cycling have ...extremely restricted its practical applications for energy storage devices. Here, a thermal infusion strategy for prestoring lithium into a stable nickel foam host is demonstrated and a composite anode is achieved. In comparison with the bare lithium, the composite anode exhibits stable voltage profiles (200 mV at 5.0 mA cm−2) with a small hysteresis beyond 100 cycles in carbonate‐based electrolyte, as well as high rate capability, significantly reduced interfacial resistance, and small polarization in a full‐cell battery with Li4Ti5O12 or LiFePO4 as counter electrode. More importantly, in addition to the fact that lithium is successfully confined in the metallic nickel foam host, uniform lithium plating/stripping is achieved with a low dimension change (merely ≈3.1%) and effective inhibition of dendrite formation. The mechanism for uniform lithium stripping/plating behavior is explained based on a surface energy model.
A Li–Ni composite anode is achieved via a thermal infusion strategy. It exhibits stable voltage profiles (90 mV at 1.0 mA cm−2) with small hysteresis beyond 100 cycles, as well as low dimension change and effective dendrite inhibition after 100 cycles in a symmetric cell.
Aiming at the construction of novel platform for efficient light harvesting, the precise synthesis of a new family of AIEgen‐branched rotaxane dendrimers was successful realized from an ...AIEgen‐functionalized 2rotaxane through a controllable divergent approach. In the resultant AIE macromolecules, up to twenty‐one AIEgens located at the tails of each branches, thus making them the first successful example of AIEgen‐branched dendrimers. Attributed to the solvent‐induced switching feature of the rotaxane branches, the integrated rotaxane dendrimers displayed interesting dynamic feature upon the aggregation‐induced emission (AIE) process. Moreover, novel artificial light‐harvesting systems were further constructed based on these AIEgen‐branched rotaxane dendrimers, which revealed impressive generation‐dependent photocatalytic performances for both photooxidation reaction and aerobic cross‐dehydrogenative coupling (CDC) reaction.
A novel artificial light‐harvesting system based on AIEgen‐branched rotaxane dendrimers has been successfully constructed which displayed impressive generation‐dependent photocatalytic performances for both photooxidation reaction and aerobic cross‐dehydrogenative coupling reaction.
This paper is devoted to design an event-triggered data-driven control for a class of disturbed nonlinear systems with quantized input. A uniform quantizer reconstructed with decreasing quantization ...intervals is employed to reduce the quantization error. A neural network-based estimation strategy is proposed to estimate both the pseudo partial derivative and disturbances. Consequently, an input triggering rule for single-input single-output systems is provided by incorporating the estimated disturbances, the quantization error bound and tracking errors. Resorting to the Lyapunov method, sufficient conditions for synthesized error systems to be uniformly ultimately bounded are presented. The validity of the proposed scheme is demonstrated via a simulation example.
The idea of translanguaging has disrupted much of the thinking in bilingual education. A common misunderstanding, however, is that translanguaging was intended to be a language teaching strategy. ...This article seeks to explore what a translanguaging approach to language teaching entails, with specific reference to the education of minoritized and racialized bilingual and multilingual learners in the school systems in English-dominant countries such as the UK. In particular, I highlight the connections with and contributions to the inclusion and social justice agenda that the translanguaging project aims to make. Translanguaging takes one step further from multilingualism in challenging the raciolinguistic ideologies that view bilingual learners as having separate languages and languaging lives. It instead views their racial/ethnic identities and linguistic practices together, that is, their translanguaging being. My main argument here is that to use translanguaging as a pedagogy for inclusion and social justice requires a change of mindset, not just practice – that is, translanguaging pedagogy rather than pedagogical translanguaging – which can be achieved through processes of ‘co-learning’ and ‘transpositioning’.
Aluminum‐ion batteries (AIBs) attract interest for their promising features of superior safety and long‐life energy storage. Organic materials with engineered active groups are considered promising ...for promoting energy storage capabilities. However, the corresponding energy density (both voltage plateau and sufficient active sites required) and stability are still unexpectedly poor. To address these challenges, here π‐conjugated organic porphyrin molecules, that is, 5,10,15,20‐tetraphenylporphyrin (H2TPP) and 5,10,15,20‐tetrakis(4‐carboxyphenyl) porphyrin (H2TCPP), are selected as the positive electrode materials for AIBs. Owing to the highly reversible coordination/dissociation with aluminum complex cations, H2TPP presents long‐term cycling stability beyond 5000 cycles at 200 mA g−1. Compared with the specific capacity of H2TCPP (≈24 mA h g−1 at 100 mA g−1), the enhanced capabilities in H2TPP (reversible specific capacity of ≈101 mA h g−1 at 100 mA g−1) are attributed to removal of the carboxyl functional groups, which plays a role in reducing the basicity of porphyrin induced via electron withdrawing effects. Additionally, the mechanism of electrochemical reaction between AlCl2+ and porphyrin as well as ionic diffusion behaviors on the surface of the electrode are investigated. The results establish a platform to develop long‐term organic aluminum batteries for safe and stable energy storage.
Stable high‐capacity organic aluminum–porphyrin batteries are assembled and the large delocalized π bond in porphyrins can effectively promote the active sites and improve stability of the molecular structures. These features allow the aluminum–porphyrin batteries to deliver long‐term stability and high rate capabilities, which enable the fabrication of a high‐capacity organic Aluminum‐ion batteries.
Boron is an interesting element with unusual polymorphism. While three-dimensional (3D) structural motifs are prevalent in bulk boron, atomic boron clusters are found to have planar or quasi-planar ...structures, stabilized by localized two-center–two-electron (2c–2e) σ bonds on the periphery and delocalized multicenter–two-electron (nc–2e) bonds in both σ and π frameworks. Electron delocalization is a result of boron’s electron deficiency and leads to fluxional behavior, which has been observed in B13 + and B19 –. A unique capability of the in-plane rotation of the inner atoms against the periphery of the cluster in a chosen direction by employing circularly polarized infrared radiation has been suggested. Such fluxional behaviors in boron clusters are interesting and have been proposed as molecular Wankel motors. The concepts of aromaticity and antiaromaticity have been extended beyond organic chemistry to planar boron clusters. The validity of these concepts in understanding the electronic structures of boron clusters is evident in the striking similarities of the π-systems of planar boron clusters to those of polycyclic aromatic hydrocarbons, such as benzene, naphthalene, coronene, anthracene, or phenanthrene. Chemical bonding models developed for boron clusters not only allowed the rationalization of the stability of boron clusters but also lead to the design of novel metal-centered boron wheels with a record-setting planar coordination number of 10. The unprecedented highly coordinated borometallic molecular wheels provide insights into the interactions between transition metals and boron and expand the frontier of boron chemistry. Another interesting feature discovered through cluster studies is boron transmutation. Even though it is well-known that B–, formed by adding one electron to boron, is isoelectronic to carbon, cluster studies have considerably expanded the possibilities of new structures and new materials using the B–/C analogy. It is believed that the electronic transmutation concept will be effective and valuable in aiding the design of new boride materials with predictable properties. The study of boron clusters with intermediate properties between those of individual atoms and bulk solids has given rise to a unique opportunity to broaden the frontier of boron chemistry. Understanding boron clusters has spurred experimentalists and theoreticians to find new boron-based nanomaterials, such as boron fullerenes, nanotubes, two-dimensional boron, and new compounds containing boron clusters as building blocks. Here, a brief and timely overview is presented addressing the recent progress made on boron clusters and the approaches used in the authors’ laboratories to determine the structure, stability, and chemical bonding of size-selected boron clusters by joint photoelectron spectroscopy and theoretical studies. Specifically, key findings on all-boron hydrocarbon analogues, metal-centered boron wheels, and electronic transmutation in boron clusters are summarized.
A series of twisted D–π–A type emitters based on the acridine donor unit and CN‐substituted pyridine, pyrimidine, and benzene acceptor units are studied. They not only allow one to systematically ...probe the influence of different acceptor strengths, but also permit one to intriguingly probe the influence of tunable conformations (twist angles) within the acceptor moieties through controlling the orientation of asymmetric heteroaromatic ring relative to the donor component. Intramolecular charge‐transfer transitions are observed in all these compounds and emission wavelengths are widely tunable from deep blue to yellow not only by the general acceptor strength due to the characters of heteroarene and CN‐substitution pattern but also by the subtle control of in‐acceptor conformation (twist angles). Small triplet‐to‐singlet energy gaps (ΔEST) and significant thermally activated delayed fluorescence (TADF) characteristics are obtained in a series of D–π–A compounds with sufficient acceptor strengths and tunable in‐acceptor conformation, yielding a series of efficient blue‐green to yellow TADF emitters with promisingly high photoluminescence quantum yields of 90%–100%. Highly efficient blue‐green to yellow TADF organic light‐emitting diodes (OLEDs) having external quantum efficiencies of up to 23.1%–31.3% are achieved using these efficient TADF emitters, which are among the most efficient TADF OLEDs ever reported.
Efficient blue‐green to yellow thermally activated delayed fluorescence emitters capable of generating 23%–31% electroluminescence external quantum efficiencies are developed adopting the acridine donor unit and cyano (CN)‐substituted pyridine and pyrimidine acceptor units. They permit systematic probing of influences of acceptor strengths and tunable conformations (twist angles) within the acceptor moieties through controlling the orientation of asymmetric heteroaromatic ring.
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