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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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Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

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Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
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Metal-Ligand Bonds02:51

Metal-Ligand Bonds

21.5K
The hemoglobin in the blood, the chlorophyll in green plants, vitamin B-12, and the catalyst used in the manufacture of polyethylene all contain coordination compounds. Ions of the metals, especially the transition metals, are likely to form complexes.
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...
21.5K
Crystal Field Theory - Tetrahedral and Square Planar Complexes02:46

Crystal Field Theory - Tetrahedral and Square Planar Complexes

44.7K
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 Solids02:18

Network Covalent Solids

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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.
To break or to melt a covalent network solid, covalent bonds must be broken. Because covalent bonds are relatively strong, covalent network solids are typically...
14.5K
Chemical Shift: Internal References and Solvent Effects01:17

Chemical Shift: Internal References and Solvent Effects

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In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...
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Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks
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金属有机框架中的旋转交叉:一个嵌入晶体的多参考研究.

I Popov1, A Tchougréeff2, E Besley1

  • 1School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom.

The Journal of chemical physics
|August 6, 2025
PubMed
概括
此摘要是机器生成的。

周期有效的晶场哈密尔顿式 (pEHCF) 方法准确地模拟了自旋交叉 (SCO) 材料. 计算揭示了影响Fe (pyridine) 2Ni (CN) 4和Fe2 (H0.67bdt) 3金属有机框架 (MOF) 中SCO行为的关键因素.

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科学领域:

  • 固态化学和材料科学 固态化学和材料科学
  • 计算凝聚物质物理学 计算凝聚物质物理学
  • 量子化学是一种量子化学.

背景情况:

  • 过渡金属 (TM) 材料中的旋转交叉 (SCO) 由于多参考电子状态而带来计算挑战.
  • 准确的电子结构计算对于理解和设计SCO材料至关重要.

研究的目的:

  • 在特定的金属有机框架 (MOF) 中应用周期有效的晶场哈密尔顿法 (pEHCF) 来研究SCO.
  • 为了研究Fe (pyridine) 2Ni (CN) 4和Fe2 (H0.67bdt) 3MOF中的电子结构和旋转状态转换.

主要方法:

  • 使用周期有效的晶体场哈密尔顿式 (pEHCF) 方法进行电子结构计算.
  • 计算了自旋状态的相对能量,并确定了退化线.
  • 分析了自旋状态对联体位置和原子间距离的依赖性.

主要成果:

  • 在Fe(pyridine) 2Ni(CN) 4 MOF中确定了一条严重依赖Fe-CN距离的退化线,并且显示了与pyridine连接体位置相似的阶段性行为.
  • 通过Ni的三重基态解释了Fe ((pyridine) 2Ni ((CN) 4MOF的低温磁性.
  • 证实了Fe2中Fe2离子从五重奏到单重奏的旋转转变Fe2中Fe2 ((H0.67bdt) 3MOF在300-423K之间,而Fe1离子保持低旋转.

结论:

  • 在含有TM的晶体系统中,pEHCF方法有效计算SCO特性.
  • 结构参数在研究的MOF中显著影响SCO行为.
  • 这些发现提供了对复杂材料中旋转交叉作用的机制的见解.