Hydrothermal Synthesis and Structure of a New 3D Lanthanide—Carboxylate Framework,[La（btec）1／2（H2btec）1／2（H2O）]n（H4btec=1,2,4,5—Benzeneteracarboxylic acid）

The title complex, [La(btec)_1/2(H₂btec)_1/2 (H₂O)]_n (H₄btec= 1, 2,4,5‐benzenetetracarboxylic acid) (1) was synthesized by the hydrothermal reaction of 1,2,4,5‐benzenetetracarboxylic dianhydride with La(NO₃)₃·6H₂O in H₂O, and crystallizes in the triclinic system, space group P‐1 with a = 0.64403(3) nm, b = 0.94500(4) nm, c = 0.96380(5) nm, a = 88.535(2)°, β = 100.314(2)°, γ = 76.6470(10)°, V = 1.60968(10) nm³, Z = 2, and final R = 0.0274, R_w = 0.0735. In 1, each La(m) ion is coordinated by eight oxygen atoms from six carboxylate groups and one coordinated water molecule. Two different coordination modes of H₄btec were present in the structure, one of which contains two protonated carboxylate groups to balance the charge.     

A High－efficiency Preparation, Properties and Structure of （R, S ）－and （ S, S）－Pyrrolidine－2－carboxylic Acid 3,5－Dioxa－4－boracvclo.hepta [ 2,1－α; 3,4－α′] dinaphthalen－4－yl Esters

A highly-efficient preparative procedure for ( R, S )- and ( S, S)-pyrroHdine-2-carboxyHc acid 3,5-dioxa-4-boracyclohepta[2, 1-α ; 3,4-α′] dlnaphthalen-4-yl esters [ namely ( R, S )-BNBAP and (S, S )-BNBAP] is described and the crystal structure of (R, S )-BNBAP was obtained. The data indicate that ( R, S )-BNBAP is a spirocyclic inner borate salt with almost normal te-trahedral configuration. This structural form may be the basic reason for their high chemical, optical and thermodynamic sta-bility.     

Highly efficient electrocatalytic hydrogen evolution promoted by O–Mo–C interfaces of ultrafine β-Mo2C nanostructures

Optimizing interfacial contacts and thus electron transfer phenomena in heterogeneous electrocatalysts is an effective approach for enhancing electrocatalytic performance. Herein, we successfully synthesized ultrafine β-Mo₂C nanoparticles confined within hollow capsules of nitrogen-doped porous carbon (β-Mo₂C@NPCC) and found that the surface layer of molybdenum atoms was further oxidized to a single Mo–O surface layer, thus producing intimate O–Mo–C interfaces. An arsenal of complementary technologies, including XPS, atomic-resolution HAADF-STEM, and XAS analysis clearly reveals the existence of O–Mo–C interfaces for these surface-engineered ultrafine nanostructures. The β-Mo₂C@NPCC electrocatalyst exhibited excellent electrocatalytic activity for the hydrogen evolution reaction (HER) in water. Theoretical studies indicate that the highly accessible ultrathin O–Mo–C interfaces serving as the active sites are crucial to the HER performance and underpinned the outstanding electrocatalytic performance of β-Mo₂C@NPCC. This proof-of-concept study opens a new avenue for the fabrication of highly efficient catalysts for HER and other applications, whilst further demonstrating the importance of exposed interfaces and interfacial contacts in efficient electrocatalysis.

Ultrafine β-Mo₂C nanostructures encapsulated in N-doped carbon capsules featuring O–Mo–C interfaces as the active sites for HER have been unveiled.     

Poly[[diaquamanganese(II)]‐μ3‐4‐oxido‐2‐oxo‐1,2‐dihydropyrimidine‐5‐carboxylato‐κ4O4,O5:O2:O2]

In the title compound, [Mn(C₅H₂N₂O₄)(H₂O)₂]_n, the Mn^II ion has a distorted octahedral geometry and the 4‐oxido‐2‐oxo‐1,2‐dihydropyrimidine‐5‐carboxylate (Hiso²⁻) anion acts as a μ₃:η⁴‐bridging ligand. Two oxo O atoms from different Hiso²⁻ ligands bridge two Mn^II ions, forming centrosymmetric dinuclear building blocks. Each dinuclear building block interacts with another four by the coordination of the oxide groups and carboxylate O atoms, producing a two‐dimensional framework in the ab plane. Hydrogen bonds further extend the two‐dimensional sheets into a three‐dimensional supramolecular framework.     

SPME-GC-MSD for Determination of Nine Phenyl Compounds in Snow Water in Beijing China

Solid phase microextraction (SPME) then capillary gas chromatography with mass spectrometric detection have been used for determination of nine phenyl compounds in snow water in Beijing City. Headspace extraction with a fiber coated with 100 µm PDMS was used to extract the compounds. Extraction and desorption times were optimized at 8 and 2 min, respectively. Relative standard deviation (RSD) of the analytical method was found to be less than 5%. The linear range was wide and limits of detection were less than 5 ng mL⁻¹ for the nine target analytes. Several phenyl compounds at ng mL⁻¹ levels were detected in snow samples in Beijing, indicating the corresponding air pollution.     

Preparation and characterization of vanadium(IV) oxide supported on SBA-15 and its catalytic performance in benzene hydroxylation to phenol using molecular oxygen

Preparation of dispersed transition metal oxides catalyst with low oxidation state still remains a challenging task in heterogeneous catalysis.In this study,vanadium oxides supported on zeolite SBA-15 have been prepared under hydrothermal condition using V 2 O 5 and oxalic acid as sources of vanadium and reductant,respectively.The structures of samples,especially the oxidation state of vanadium,and the surface distribution of vanadium oxide species,have been thoroughly characterized using various techniques,including N 2-physisorption,X-ray diffraction(XRD),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),UV-visible spectra(UV-Vis) and UV-visible-near infrared spectra(UV-Vis-NIR).It is found that the majority of supported vanadium was in the form of vanadium(IV) oxide species with the low valence of vanadium.By adjusting hydrothermal treatment time,the surface distribution of vanadium(IV) oxide species can be tuned from vanadium(IV) oxide cluster to crystallites.These materials have been tested in the hydroxylation of benzene to phenol in liquid-phase with molecular oxygen in the absence of reductant.The catalyst exhibits high selectivity for phenol(61%) at benzene conversion of 4.6%,which is a relatively good result in comparison with other studies employing molecular oxygen as the oxidant.     

Epoxidation reaction of perfluoroalkenes with tert-amine N-oxide

Straight-chain aliphatic terr-amine N-oxides were found to be useful oxidizing agent for epoxidation of tri- and tetra-substituted perfluoroalkenes under mild conditions in high yields.The process for epoxidation by employing tri-n-butylamine N-oxide gave the best result in the reagent survey.     

杠杆教学的高端备课

从杠杆的本质出发,提出杠杆是“放大”或“缩小”力的装置.按照从特殊到一般的顺序进行杠杆的教学,通过强化研究思路,全面介绍杠杆分类,从而使杠杆教学达到一个新的水平.     

Tailorable PC71BM Isomers: Using the Most Prevalent Electron Acceptor to Obtain High‐Performance Polymer Solar Cells

Despite being widely used as electron acceptor in polymer solar cells, commercially available PC₇₁BM (phenyl‐C₇₁‐butyric acid methyl ester) usually has a “random” composition of mixed regioisomers or stereoisomers. Here PC₇₁BM has been isolated into three typical isomers, α‐, β₁‐ and β₂‐PC₇₁BM, to establish the isomer‐dependent photovoltaic performance on changing the ternary composition of α‐, β₁‐ and β₂‐PC₇₁BM. Mixing the isomers in a ratio of α/β₁/β₂=8:1:1 resulted in the best power conversion efficiency (PCE) of 7.67 % for the polymer solar cells with PTB7:PC₇₁BM as photoactive layer (PTB7=poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl]]). The three typical PC₇₁BM isomers, even though sharing similar LUMO energy levels and light absorption, render starkly different photovoltaic performances with average‐performing PCE of 1.28–7.44 % due to diverse self‐aggregation of individual or mixed PC₇₁BM isomers in the otherwise same polymer solar cells.