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相关概念视频

Crystal Field Theory - Octahedral Complexes02:58

Crystal Field Theory - Octahedral Complexes

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Crystal Field Theory
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
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Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
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Network covalent solids contain a three-dimensional network of covalently bonded atoms as found in the crystal structures of nonmetals like diamond, graphite, silicon, and some covalent compounds, such as silicon dioxide (sand) and silicon carbide (carborundum, the abrasive on sandpaper). Many minerals have networks of covalent bonds.
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Cyclohexane does not exist in a planar form due to the high angle and torsional strain it would experience in the planar structure. Instead, it adopts non-planar chair and boat conformations.
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Physical models representing molecular architectures of chemical compounds play essential roles in understanding chemistry. The use of molecular models makes it easier to visualize the structures and shapes of atoms and molecules.
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Adolf von Baeyer attempted to explain the instabilities of small and large cycloalkane rings using the concept of angle strain — the strain caused by the deviation of bond angles from the ideal 109.5° tetrahedral value for sp3  hybridized carbons. However, while cyclopropane and cyclobutane are strained, as expected from their highly compressed bond angles, cyclopentane is more strained than predicted, and cyclohexane is virtually strain-free. Hence, Baeyer’s theory that...
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通过合规设计选择性结晶的3D共价有机框架

Ha L Nguyen1,2, Cornelius Gropp1, Yanhang Ma3

  • 1Department of Chemistry, University of California Berkeley; Kavli Energy Nanoscience Institute at UC Berkeley; and Berkeley Global Science Institute, Berkeley, California 94720, United States.

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|November 13, 2020
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概括

研究人员设计了三角形和正方形建筑单元,以选择性地形成具有高表面积的晶体内共价有机框架 (COF). 这种形状控制是实现所需的拓和材料性能的关键.

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科学领域:

  • 材料科学
  • 化学学
  • 纳米技术

背景情况:

  • 共价有机框架 (COF) 是具有可调的晶体多孔聚合物.
  • 具有特定拓和高晶度的COF选择性合成仍然是一个挑战.
  • 控制建筑单元的形状对于定向框架组装至关重要.

研究的目的:

  • 开发一种具有fjh拓的选择性COF形成的策略.
  • 研究建筑单元在COF结晶中的作用.
  • 合成和描述具有高表面积的新型COF.

主要方法:

  • 三角形 (TTFB) 和方形 (ETTA) 建筑单元的构造设计.
  • 设计为形成 imine COF 的单元的网状结构.
  • 使用光谱,显微和X射线衍射技术进行表征.
  • 使用BET方法进行孔径和表面积分析.

主要成果:

  • 实现了具有fjh拓的选择性晶体胺COF,COF-790.
  • COF-790具有2650 m2的高布鲁纳尔-埃梅特-泰勒 (BET) 表面积.
  • 预先设计的建筑单元结构 (二面角75-90°) 对于晶体产品的形成至关重要.
  • 通过使用替代方位单位合成了两种异构型COF (COF-791和COF-792).

结论:

  • 建筑单元的合规控制是选择性COF合成的有效策略.
  • 开发的方法允许合理设计具有特定拓的晶体COF.
  • 合成的COF具有很高的孔隙性和表面积,这表明在气体储存和分离方面有潜在的应用.