多频 EPR 研究和密度函数 g-tensor 对持久性有机甲基复合物的计算
Stéphanie Frantz1, Heiko Hartmann, Natasa Doslik
1Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany.
Journal of the American Chemical Society
|August 29, 2002
概括
使用高频 EPR.研究了带有桥接配体的二核基离子复合体. 该abcp连接体增强了金属的超精密合和g异形性,由DFT计算证实.
科学领域:
- 无机化学 无机化学 有机化学
- 有机金属化学 有机金属化学
- 频谱学是一种光谱学.
背景情况:
- 的二核基离子复合物,特别是[[{mu-L}[{Re{CO}}}}}3Cl}}{2}}{*}}-其中L是2,2'-azobispyridine (abpy) 或2,2'-azobis{5-chloropyrimidine) (abcp),由于它们的电子特性而引起人们的兴趣.
- 了解这些复合体中的电子结构和金属参与对于调整它们的反应性和特性至关重要.
研究的目的:
- 为了研究二核基基离子复合体与abpy和abcp桥接连体的电子性质.
- 阐明桥接联体的pi接受能力与由此产生的g异性和金属高精度合之间的关系.
- 用理论密度函数计算来验证实验发现.
主要方法:
- 在冷溶液上,以各种频率 (9.5,94,230,285 GHz) 进行了电子磁共振 (EPR) 谱学.
- 红外 (IR) 和UV/Vis光谱学被用来描述氧化还原系统的特征.
- 密度函数理论 (DFT) 的计算被用来建模电子结构和预测EPR参数.
主要成果:
- 高频EPR实验揭示了不同的g组件,与X频段测量不同,X频段测量只提供同位素金属高精度合.
- 与abpy复合体相比,abcp复合体,具有更强的pi-接受联体,表现出更大的a 185,187 Re) 值和g异构性 (g 1 - g 3)).
- DFT计算支持实验观测,表明abcp系统在单独占用的分子轨道中金属的参与更大,从而提高了g的异构性.
结论:
- 桥接联体的pi接受能力显著影响二核基离子复合物的电子特性和EPR参数.
- 高频EPR对于解决异构相互作用和更深入了解这种复杂物体电子结构至关重要.
- 计算方法有效地补充实验数据,为旋转密度分布和g异构的观察趋势提供理论基础.
相关概念视频
02:30Stability of Substituted Cyclohexanes
This lesson discusses the stability of substituted cyclohexanes with a focus on energies of various conformers and the effect of 1,3-diaxial interactions.
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
01:20¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)
When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...
01:28Stability of Conjugated Dienes
Introduction
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
01:37NMR Spectroscopy of Benzene Derivatives
Simple unsubstituted benzene has six aromatic protons, all chemically equivalent. Therefore, benzene exhibits only a singlet peak at δ 7.3 ppm in the 1H NMR spectrum. The observed shift is far downfield because the aromatic ring current strongly deshields the protons. Any substitution on the benzene ring makes the aromatic protons nonequivalent, and the protons split each other. The peak is, therefore, no longer a singlet and the splitting pattern and their associated coupling constants depend...
01:17Electron Paramagnetic Resonance (EPR) Spectroscopy: Organic Radicals
Ideally, an unpaired electron shows a single peak in the EPR spectrum due to the transition between the two spin energy states. However, coupling interactions can occur between the spins of the unpaired electron and any neighboring spin-active nuclei. This hyperfine coupling results in hyperfine splitting, where the EPR signal is split into multiplets. The signals split into 2nI + 1 peaks, where n is the number of equivalent nuclei and I is the nuclear spin. These splitting patterns provide...
01:12Double Resonance Techniques: Overview
Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...
Spin decoupling is usually achieved by...