Generic applications of 13C‐detected NMR diffusion to formulated systems with suppression of thermal convection induced by proton decoupling

Fast and effective structural/compositional analysis on formulated systems represents one of the major challenges encountered in analytical science. ¹³C‐detected diffusion represents a promising tool to tackle the aforementioned challenges, particularly in industry. Toward exploring the generic applications of ¹³C‐detected diffusion, thermal convection induced by ¹H decoupling has been identified as a key factor that resulted in significantly reduced resolution in the diffusion dimension. Optimization of experimental parameters and utilization of double‐stimulated echo‐based pulse sequence both can effectively suppress the thermal convection caused by the ¹H decoupling, the success of which allows robust and generic applications of ¹³C‐detected diffusion to systems from mixtures of small molecules, polymer blends, and copolymers to actual complex formulated systems. The method is particularly powerful in differentiating small molecules from polymers, polymer blends from copolymers, and end‐group analysis. Copyright © 2016 John Wiley & Sons, Ltd.     

Creating Coordination‐Based Cavities in a Multiresponsive Supramolecular Gel

Creating cavities in varying levels, from molecular containers to macroscopic materials of porosity, have long been motivated for biomimetic or practical applications. Herein, we report an assembly approach to multiresponsive supramolecular gels by integrating photochromic metal–organic cages as predefined building units into the supramolecular gel skeleton, providing a new approach to create cavities in gels. Formation of discrete O‐Pd₂L₄ cages is driven by coordination between Pd²⁺ and a photochromic dithienylethene bispyridine ligand (O‐PyFDTE). In the presence of suitable solvents (DMSO or MeCN/DMSO), the O‐Pd₂L₄ cage molecules aggregate to form nanoparticles, which are further interconnected through supramolecular interactions to form a three‐dimensional (3D) gel matrix to trap a large amount of solvent molecules. Light‐induced phase and structural transformations readily occur owing to the reversible photochromic open‐ring/closed‐ring isomeric conversion of the cage units upon UV/visible light radiation. Furthermore, such Pd₂L₄ cage‐based gels show multiple reversible gel–solution transitions when thermal‐, photo‐, or mechanical stimuli are applied. Such supramolecular gels consisting of porous molecules may be developed as a new type of porous materials with different features from porous solids.     

Estimation of partially specified spatial panel data models with random-effects

In this article, we study estimation of a partially specified spatial panel data linear regression with random-effects. Under the conditions of exogenous spatial weighting matrix and exogenous regressors, we give an instrumental variable estimation. Under certain sufficient assumptions, we show that the proposed estimator for the finite dimensional parameter is root-N consistent and asymptotically normally distributed and the proposed estimator for the unknown function is consistent and asymptotically distributed. Consistent estimators for the asymptotic variance-covariance matrices of both the parametric and unknown components are provided. The Monte Carlo simulation results verify our theory and suggest that the approach has some practical value.     

Hierarchically Designed Three‐Dimensional Macro/Mesoporous Carbon Frameworks for Advanced Electrochemical Capacitance Storage

Mesoporous carbon (m‐C) has potential applications as porous electrodes for electrochemical energy storage, but its applications have been severely limited by the inherent fragility and low electrical conductivity. A rational strategy is presented to construct m‐C into hierarchical porous structures with high flexibility by using a carbon nanotube (CNT) sponge as a three‐dimensional template, and grafting Pt nanoparticles at the m‐C surface. This method involves several controllable steps including solution deposition of a mesoporous silica (m‐SiO₂) layer onto CNTs, chemical vapor deposition of acetylene, and etching of m‐SiO₂, resulting in a CNT@m‐C core–shell or a CNT@m‐C@Pt core–shell hybrid structure after Pt adsorption. The underlying CNT network provides a robust yet flexible support and a high electrical conductivity, whereas the m‐C provides large surface area, and the Pt nanoparticles improves interfacial electron and ion diffusion. Consequently, specific capacitances of 203 and 311 F g^?1 have been achieved in these CNT@m‐C and CNT@m‐C@Pt sponges as supercapacitor electrodes, respectively, which can retain 96 % of original capacitance under large degree compression.     

Copper‐Catalyzed Difunctionalization of Activated Alkynes by Radical Oxidation–Tandem Cyclization/Dearomatization to Synthesize 3‐Trifluoromethyl Spiro[4.5]trienones

A copper‐catalyzed difunctionalizing trifluoromethylation of activated alkynes with the cheap reagent sodium trifluoromethanesulfinate (NaSO₂CF₃ or Langlois’ reagent) has been developed incorporating a tandem cyclization/dearomatization process. This strategy affords a straightforward route to synthesis of 3‐(trifluoromethyl)‐spiro[4.5]trienones, and presents an example of difunctionalization of alkynes for simultaneous formation of two carbon–carbon single bonds and one carbon–oxygen double bond.     

Tuning the electronic properties of hydrogen passivated C3N nanoribbons through van der Waals stacking

The two-dimensional (2D) C₃N has emerged as a material with promising applications in high performance device owing to its intrinsic bandgap and tunable electronic properties. Although there are several reports about the bandgap tuning of C₃N via stacking or forming nanoribbon, bandgap modulation of bilayer C₃N nanoribbons (C₃NNRs) with various edge structures is still far from well understood. Here, based on extensive first-principles calculations, we demonstrated the effective bandgap engineering of C₃N by cutting it into hydrogen passivated C₃NNRs and stacking them into bilayer heterostructures. It was found that armchair (AC) C₃NNRs with three types of edge structures are all semiconductors, while only zigzag (ZZ) C₃NNRs with edges composed of both C and N atoms (ZZCN/ CN) are semiconductors. The bandgaps of all semiconducting C₃NNRs are larger than that of C₃N nanosheet. More interestingly, AC-C₃NNRs with CN/CN edges (AC-CN/CN) possess direct bandgap while ZZ-CN/CN have indirect bandgap. Compared with the monolayer C₃NNR, the bandgaps of bilayer C₃NNRs can be greatly modulated via different stacking orders and edge structures, varying from 0.43 eV for ZZ-CN/CN with AB′-stacking to 0.04 eV for AC-CN/CN with AA-stacking. Particularly, transition from direct to indirect bandgap was observed in the bilayer AC-CN/CN heterostructure with AA′-stacking, and the indirect-to-direct transition was found in the bilayer ZZ-CN/CN with ABstacking. This work provides insights into the effective bandgap engineering of C₃N and offers a new opportunity for its applications in nano-electronics and optoelectronic devices.     

[Nb@Ge13/14]3−: New Family Members of Ge-Based Intermetalloid Clusters

During the past two decades, single-atom-centered medium-sized germanium clusters [M@Ge_n] (M=transition metals, n>12) have been extensively explored, both from theoretical perspectives and experimental gas-phase syntheses. However, the actual structural arrangements of the Ge₁₃ and Ge₁₄ endohedral cages are still ambiguous and have long remained an unresolved problem for experimental implementation. In this work, we successfully synthesize 13-/14-vertex Ge clusters [Nb@Ge₁₃]³⁻ ( 1 ) and [Nb@Ge₁₄]³⁻ ( 2 ), which are structurally characterized and exhibit unprecedented topologies, neither classical deltahedra nor 3-connected polyhedral structures. Theoretical analysis indicates that the major stabilization of the Ge backbones arises due to the substantial interaction of Ge 4p-AOs with the endohedral Nb 4d-AOs through three/four-center two-electron bonds with an enhanced electron density accumulated over the shortest Nb−Ge13 contact in 1 . Low occupancies of the direct two-center two-electron (2c–2e) Nb−Ge and Ge−Ge σ bonds point to a considerable degree of electron delocalization over the Ge cages revealing their electron deficiency.