在Co(II) 三pyrazolylmethanes中,取决于场和温度的偏磁放松增强
Nuwanthika D Kumarage1, Amy R Marts1, Matthew P Grindle1
1Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States.
Inorganic chemistry
|September 19, 2023
概括
核磁共振对磁性放松增强揭示了二-三pyrazolylborate复合体中的Jahn-Teller动态. 这些动态影响电子放松时间和激活障碍,不同于相关的trispyrazolylborate复合体.
科学领域:
- 无机化学 无机化学
- 物理化学 物理化学
- 核磁共振光谱学 核磁共振光谱学
背景情况:
- (II) 复合物与trispyrazolylborate (Tp) 和相关联体因其有趣的电子和结构性质而闻名.
- 雅恩-泰勒动力学可以显著影响过渡金属复合物的磁性和光谱性行为.
- 偏磁放松增强剂 (PREs) 是电子自旋动力学和溶液中的分子运动的敏感探针.
研究的目的:
- 在 bis-trispyrazolylmethane (Tpm) (II) 复合物中研究 Jahn-Teller 动态,使用场和温度依赖的 NMR PREs.
- 为了确定这些动态的电子放松时间 (T1e) 和激活障碍.
- 阐明不同放松机制和分子参数对观察到的NMR数据的贡献.
主要方法:
- 综合场和温度依赖的核磁共振 (NMR) 偏磁放松增强 (PRE) 测量在[Co(Tpm) 2][BF4]2.2.
- 分析PRE数据以提取电子放松时间 (T1e) 和激活障碍.
- 密度函数理论 (DFT) 和完整的活性空间自相一致场 (CASSCF) 计算以建模电子结构和振动模式.
主要成果:
- 建立了关于bis-Tpm (II) 复合体中的分子三轴Jahn-Teller动态的证据.
- 提取了电子放松时间 (T1e),显示了取决于场的行为和与相关的Tp复合体相比~40%更高的激活屏障.
- 灵敏度 (库里) 放松对线宽有显著的贡献 (20-35%),而9.5 Å的分子半径表明对比的影响.
结论:
- 该研究证实了[Co(Tpm) 2+中的Jahn-Teller动态,并将电子相关时间的差异归因于更高的Jahn-Teller激活屏障.
- 核磁共振试验对复合物的电子结构,分子动力学和放松过程之间的相互作用提供了宝贵的见解.
- 这些发现强调了将实验性NMR光谱学与理论计算相结合的实用性,以进行详细的机理学研究.
相关概念视频
Colors and Magnetism
11.8K
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...
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...
11.8K
Atomic Nuclei: Nuclear Relaxation Processes
676
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.
676
Paramagnetism
2.5K
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...
2.5K
¹H NMR: Interpreting Distorted and Overlapping Signals
1.1K
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
1.1K
NMR Spectroscopy: Spin–Spin Coupling
1.5K
The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved...
1.5K
Atomic Nuclei: Types of Nuclear Relaxation
323
Nuclear relaxation restores the equilibrium population imbalance and can occur via spin–lattice or spin–spin mechanisms, which are first-order exponential decay processes.
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers...
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers...
323


![Measuring the Spin-Lattice Relaxation Magnetic Field Dependence of Hyperpolarized [1-13C]pyruvate](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F59399.jpg&w=3840&q=50)