Phase Stability and Elastic Properties of Chromium Borides with Various Stoichiometries

Phase stability is important to the application of materials. By first‐principles calculations, we establish the phase stability of chromium borides with various stoichiometries. Moreover, the phases of CrB₃ and CrB₄ have been predicted by using a newly developed particle swarm optimization (PSO) algorithm. Formation enthalpy–pressure diagrams reveal that the MoB‐type structure is more energetically favorable than the TiI‐type structure for CrB. For CrB₂, the WB₂‐type structure is preferred at zero pressure. The predicted new phase of CrB₃ belongs to the hexagonal P‐6m2 space group and it transforms into an orthorhombic phase as the pressure exceeds 93 GPa. The predicted CrB₄ (space group: Pnnm) phase is more energetically favorable than the previously proposed Immm structure. The mechanical and thermodynamic stabilities of predicted CrB₃ and CrB₄ are verified by the calculated elastic constants and formation enthalpies. The full phonon dispersion calculations confirm the dynamic stability of WB₂‐type CrB₂ and predicted CrB₃. The large shear moduli, large Young’s moduli, low Poisson ratios, and low bulk and shear modulus ratios of CrB₄? PS_C and CrB₄? PS_D indicate that they are potential hard materials. Analyses of Debye temperature, electronic localization function, and electronic structure provide further understanding of the chemical and physical properties of these borides.     

Visible‐Light‐Active Elemental Photocatalysts

Seeking visible‐light‐active photocatalysts for efficient solar‐energy conversion has become an intensifying endeavor worldwide. In this concept paper, general requirements for finding new visible‐light‐active photocatalysts are briefly introduced, and recent progress in exploring elemental photocatalysts for clean‐energy generation and environmental remediation are reviewed. Finally, opportunities and challenges facing elemental photocatalysts are discussed.     

Self‐Assembly of Anionic Porphyrins and Alkaline or Alkaline Earth Metal Ions Mediated by Cucurbit[7,8]uril

Nanoscaled coordination polymers based on biologically prevalent ions have potential applications in drug delivery and biomedical imaging. Herein, coordination polymer nanoparticles of anionic porphyrins, including meso‐tetra(4‐carboxyphenyl)‐porphyrin (H₂TCPP^4?) and meso‐tetra(4‐sulfonatophenyl)‐porphyrin (H₂TPPS^4?), and alkaline or alkaline earth metal cations, such as K⁺ and Ca²⁺, were constructed in aqueous solution in the presence of cucurbit[7]uril (CB7) or cucurbit[8]uril (CB8). UV/Vis absorption and fluorescence spectroscopy, dynamic light scattering (DLS), scanning electron spectroscopy (SEM), and atomic force microscopy (AFM) were applied to explore the assembly and particle formation of porphyrin anions and metal cations mediated by CBn. The particle size depends on the kinds of CBn and metal cations and their concentrations. The uptake of H₂TPPS^4? particles by tumor cells (A549 cells) was found to be more efficient than H₂TPPS^4? at 37 °C, showing the application potential of such assembled particles in biology and medicine.     

基于偶氮联吡啶配体的银和钴配位聚合物的构筑与性质

通过将2个4,4''-联吡啶基团用偶氮基团连接,我们合成了新的配体顺式-和反式-1,2-二（（4,4''-联吡啶）-3-氮烯）（cis-L和trans-L）,并利用trans-L与银离子和钴离子构筑了配位聚合物{[Ag₂（trans-L）（ClO₄）₂]·4CH₃CN}_n（1）和{[Co（trans-L）₂（H₂O）₂]（ClO₄）₂}_n（2）。其中1为一维梯形链,链与链之间通过π-π以及Ag…Ag相互作用堆积;2为三维无限dendrimer结构,其Co中心具有合适的氧化还原电位,在以荧光素为光敏剂的条件下,可作为光催化剂实现光解水放氢。     

Copper-and Silver-Mediated Cyanation of Aryl Iodides Using DDQ as Cyanide Source

A new copper and silver‐mediated cyanation of aryl iodides with DDQ as a cyanide source is achieved, providing nitriles with good yields. This new approach represents a safe method leading to aryl nitriles.