Exploration of New Birefringent Crystals in Bismuth d0 Transition Metal Selenites

The first examples of bismuth fluoride selenites with d⁰-TM/Te^VI polyhedrons, namely, Bi₄TiO₂F₄(SeO₃)₄ ( 1 ), Bi₄NbO₃F₃(SeO₃)₄ ( 2 ), Bi₄TeO₄F₂(TeO₃)₂(SeO₃)₂ ( 3 ), Bi₂F₂(MoO₄)(SeO₃) ( 4 ) and Bi₂ZrO₂F₂(SeO₃)₂ ( 5 ) have been successfully synthesized under hydrothermal reactions by aliovalent substitution. The five new compounds feature three different types of structures. Compounds 1 – 3 , containing Ti^IV, Nb^V and Te^VI respectively, are isostructural, exhibiting a new 3D framework composed of a 3D bismuth oxyfluoride architecture, with intersecting tunnels occupied by d⁰-TM/Te^VI octahedrons and selenite/tellurite groups. Interestingly, compound Bi₄TeO₄F₂(TeO₃)₂(SeO₃)₂ ( 3 ) is the first structure containing Se^IV and mixed-valent Te^IV/Te^VI cations simultaneously. Compound 4 features a new 3D structure formed by a 3D bismuth oxyfluoride network with MoO₄ tetrahedrons and selenites groups imbedded in the 1D tunnels. Compound 5 displays a novel pillar-layered 3D open framework, consisting of 2D bismuth oxide layers bridged by the [ZrO₂F₂(SeO₃)₂]⁶⁻ polyanions. Theoretical calculations revealed that the five compounds displayed very strong birefringence. The birefringence values of compounds 1 – 3 , especially, are above 0.19 at 1064 nm, which are larger than the mineral calcite. Based on the structure and property analysis, it was found that the asymmetric SeO₃ groups (and TeO₃ in compound 3 ) displayed the largest anisotropy, compared with the bismuth cations and the d⁰-TM/Te polyhedra, which is beneficial to the birefringence.     

Preparation of a Lanthanide–Titanium Oxo Cluster–Polymer Composite by CuI-Catalyzed Click Chemistry

Incorporating metal clusters within the skeleton of the organic polymers through a click reaction cannot only effectively prepare cluster–polymer composites, but also effectively avoid the cluster aggregation. Herein, an azide-containing lanthanide–titanium oxo cluster of Eu₈Ti₁₀-N₃ ( Eu₈Ti₁₀-N₃ =[Eu₈Ti₁₀(μ₃-O)₁₄(H₂O)₄(OAc)₂(tbba)₃₀(paza)₄(THF)₂] ⋅ 4 THF ⋅ 8 H₂O ( 1 ), Htbba=4-tert-butylbenzoic acid, Hpaza=4-azidobenzoate, HOAc=acetic acid, THF=tetrahydrofuran) through an in situ solvothermal reaction of 4-azidobenzoic acid and 4-tert-butylbenzoic acid. Reaction of 1 with PEG ( PEG =methoxypoly(ethyleneglycol)alkyne, 2000 g mol⁻¹) through Cu^I-catalyzed click chemistry generates a lanthanide–polymer composite of Eu₈Ti₁₀-N₃@PEG ( 2 ). Investigation with IR, ¹H NMR and ICP-OES of 2 indicates that the structural integrity of 1 is maintained in 2 . Study of the luminescent properties of 1 and 2 reveals that the quantum yield of 1 itself basically remains unchanged in 2 . Significantly, the formation of 2 cannot only effectively prevent the cluster 1 from aggregation, but also greatly enhance its solubility and adhesion to the substrate. Owing to the solubility and adhesion of luminescent materials being the key to their practical application, present work is thus of great significance for the development of metal cluster–polymer composite luminescent materials.     

Preparation of Tetraethylenepentamine-Functionalized 4A Zeolite for effective removal of phosphate in water

Recently, the high-concentration phosphorus-containing wastewater has been caused lots of negative influences on aquatic environment and thus driven people to develop some effective methods to remove excess of phosphate in water. In order to solve these environmental problem, in this work, a tetraethylenepentamine (TEPA) modified 4A zeolite has been prepared and used for removing phosphate. Removal of phosphate by precipitation of 4A zeolite and electrostatic action of TEPA with phosphate were determined by scanning electron microscopy, X-ray powder diffraction and Fourier infrared spectrum, and morphology and characteristic peak of TEPA-4A zeolite before and after adsorption changed significantly. In addition, the results of batch adsorption studies showed that the pH of the solution have a significant influence on the adsorption of TEPA-4A and the biggest adsorption capacity was 23 mg/g at pH = 2.3 ± 0.2. Adsorption isotherms results showed that the process was consistent with Langmuir model and the maximum adsorption capacity could reach to 28 mg/g at 25 °C. TEPA-4A adsorption processes were spontaneous endothermic reaction, and elevated temperatures were conducive to the adsorption process through kinetics and thermodynamics results. The research of TEPA modified 4A zeolite and raw 4A zeolite provides technical support for the development of 4A zeolite instead of sodium tripolyphosphate as a new type of detergent ingredient.     

Positive Periodic Solutions of Singular Third-Order Functional Differential Equations with p-Laplacian-Like Operators

Mathematical Notes - The aim of this paper is to consider singular third-order functional differential equations with p-Laplacian-like operator of the form $$\left( {{\varphi _p}\left( {x^{\prime...     

Chemical Constituents of Ampelopsis japonica

Chemistry of Natural Compounds -     

Chromone Derivatives from the Stems of Sichuan Local Sun Cured Tobacco and Their Anti-TMV Activity

Chemistry of Natural Compounds - Two new chromone derivatives (1 and 2), together with four known (3–6) ones, were isolated from the stems of a local sun cured tobacco (Fenghuang tobacco,...     

Rhodium(III)-Catalyzed Asymmetric Access to Spirocycles through C−H Activation and Axial-to-Central Chirality Transfer

Axial-to-central chirality transfer is an important strategy to construct chiral centers, where the axially chiral reagents are mostly limited to atropomerically stable ones. Reported herein is a Rh^III-catalyzed enantioselective spiroannulative synthesis of nitrones. The coupling proceeds via C−H arylation to give an atropomerically metastable biaryl, followed by intramolecular dearomative trapping under oxidative conditions with high degree of chirality transfer.     

Imine-based covalent organic framework as photocatalyst for visible-light-induced atom transfer radical polymerization

Photoinduced atom transfer radical polymerization (ATRP) is an economical and environment-friendly method for synthesizing polymers with pre-designable structures and precise molecular weight. Although significant progress for copper-mediated photoinduced ATRP has been achieved, several drawbacks still remain, such as poor electron transfer capability and absorption bands of photocatalysts near UV region. Herein, imine-based covalent organic framework, TAPPy-TPA-COF , has been synthesized as potential heterogeneous photocatalyst for photoinduced ATRP. The “living” feature of polymerizations of methyl methacrylate (MMA) can be well controlled by efficiency maintain the balance between activation and inactivation of Cu^I and Cu^II. The chain extension experiments have further demonstrated the chain-end fidelity of polymers. Meanwhile, the catalyst recycle experiments have revealed stability of TAPPy-TPA-COF toward ATRP processes. These results support the feasibility of using COFs as heterogeneous photocatalysts for copper-mediated ATRP under visible light irradiation.     

ENHANCED BLOCK-SPARSE SIGNAL RECOVERY PERFORMANCE VIA TRUNCATED e2/e1-2 MINIMIZATION

In this paper, we investigate truncated $ℓ_2/ℓ_{1−2}$ minimization and its associated alternating direction method of multipliers (ADMM) algorithm for recovering the block sparse signals. Based on the block restricted isometry property (Block-RIP), a theoretical analysis is presented to guarantee the validity of proposed method. Our theoretical results not only show a less error upper bound, but also promote the former recovery condition of truncated ℓ₁₋₂ method for sparse signal recovery. Besides, the algorithm has been compared with some state-of-the-art algorithms and numerical experiments have shown excellent performances on recovering the block sparse signals.