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Colors and Magnetism03:02

Colors and Magnetism

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Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human...
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Valence Bond Theory02:42

Valence Bond Theory

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Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
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Trends in Lattice Energy: Ion Size and Charge02:54

Trends in Lattice Energy: Ion Size and Charge

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An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a compound is a measure of the strength of this attraction. The lattice energy (ΔHlattice) of an ionic compound is defined as the energy required to separate one mole of the solid into its component gaseous ions. For the ionic solid sodium chloride, the lattice energy is the enthalpy change of the process:
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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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Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

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In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis.
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Paramagnetism01:30

Paramagnetism

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Paramagnets are materials with unpaired electrons that possess a finite magnetic moment. In the absence of a magnetic field, these moments are randomly oriented, and thus the net moment is zero. Under an external field, a torque acting on the moments tends to align them along the field's direction. However, the random thermal motion of electrons produces a torque opposite to the external field and tries to disorient the moments. These two competing effects align only a few moments along the...
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Hyperspectral Imaging as a Tool to Study Optical Anisotropy in Lanthanide-Based Molecular Single Crystals
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与时间和总体平均结构相比,溶液中的磁性兰化物化合物的结构演变

Barak Alnami1, Jon G C Kragskow1, Jakob K Staab1

  • 1Department of Chemistry, The University of Manchester, Manchester M13 9PL, U.K.

Journal of the American Chemical Society
|June 16, 2023
PubMed
概括
此摘要是机器生成的。

在MRI对比剂中,磁性异性显著影响了对磁性转移. 动态模拟显示了很大的分子几何波动,对于准确建模NMR/MRI行为和放松时间至关重要.

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Preparation, Purification, and Characterization of Lanthanide Complexes for Use as Contrast Agents for Magnetic Resonance Imaging
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Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
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Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
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科学领域:

  • 磁共振
  • 计算化学
  • 生物物理

背景情况:

  • 在核磁共振 (NMR) 和磁共振成像 (MRI) 中,磁性敏感性异构是对磁性转移的关键.
  • 之前对C3对称的MRI对比剂的研究强调了对影响磁性异构的分子几何和溶剂相互作用的敏感性.
  • 理想化的结构模型可能无法捕捉溶液中的分子的动态性质.

研究的目的:

  • 使用ab initio分子动力学研究溶液中的基于兰他尼德的MRI对比剂的动态分子几何.
  • 了解化物-氧结合角度的动态变化如何影响单个分子水平上的磁性异性离子和磁性转移.

主要方法:

  • 初始分子动力学模拟以建模溶液中的动态分子几何.
  • 完成活跃空间自相一致场 (CASSCF) 旋转轨道计算以确定磁性异构.
  • 对O-Ln-C3角度的振荡及其与伪接触移动的相关性进行分析.

主要成果:

  • 观察到兰酸氧键与伪C3轴之间的角度的大幅度振荡.
  • 证明这些几何波动会导致伪接触 (双极) 偏磁性NMR转移的显著振荡.
  • 时间平均变化与实验数据很好地对齐, 但波动突出了静态模型的局限性.

结论:

  • 动态分子几何学在确定MRI对比剂的偏磁转移方面发挥着关键作用.
  • 理想化的结构模型不足以完全描述溶液动态及其对NMR/MRI参数的影响.
  • 这些发现需要在对磁性敏感系统中的电子和核放松时间进行先进的建模方法.