Vibrational motions and nuclear spin relaxation in paramagnetic complexes: Hexaaquonickel(II) as an example
Vibrational motions and nuclear spin relaxation in paramagnetic complexes: Hexaaquonickel(II) as an example
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DOI：
10.1063/1.1446848
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发表时间：
2002-03-08
影响因子：
4.4
通讯作者：
Kowalewski, J
中科院分区：
文献类型：
--
作者：
Kruk, D;Kowalewski, J
镍 (II) 水溶液中的质子顺磁弛豫增强 (PRE) 用由 E-g 和 T-2g 对称性的阻尼振动运动引起的电子自旋弛豫来描述。阻尼振动在分子框架中产生可变振幅和可变主方向的瞬态零场分裂 (ZFS)，并通过 Smoluchowski 方程进行建模。该模型的参数是通过两种方法的组合获得的：首先，ZFS 的量子化学计算作为镍（II）离子配位壳几何形状的函数，其次，分子动力学模拟生成金属周围水位置的轨迹。电子自旋动力学的描述以两种方式包含在 PRE 的计算中：使用传统的 Solomon-Bloembergen-Morgan 方法以及通过更一般的慢运动理论。将计算出的 PRE 作为磁场的函数（无需任何可调参数）与实验数据进行比较。计算 PRE 的两种方法彼此一致，并且与强磁场下的实验数据一致。在低场下，模型预测的 PRE 差异很大，只有通用模型与实验符合合理。 (C) 2002 年美国物理研究所。
The proton paramagnetic relaxation enhancement (PRE) in an aqueous solution of nickel(II) is described in terms of electron spin relaxation caused by damped vibrational motions of E-g and T-2g symmetry. The damped vibrations generate a transient zero-field splitting (ZFS), of variable amplitude and variable principal direction in the molecular frame, and are modeled by the Smoluchowski equation. The parameters of the model are obtained from a combination of two approaches: first, quantum-chemical calculations of the ZFS as a function of the geometry of the coordination shell of the nickel(II) ion and, second, molecular-dynamic simulations generating a trajectory of water positions around the metal. The description of the electron spin dynamics is included in the calculations of the PRE in two ways: Using the traditional Solomon-Bloembergen-Morgan approach and also by means of the more general slow-motion theory. The calculated PRE as a function of the magnetic field, free of any adjustable parameters, is compared with the experimental data. The two methods of calculating the PRE agree with each other-and with the experimental data-at high magnetic field. At low field, the models predict very different PRE, and only the general model is in reasonable agreement with the experiments. (C) 2002 American Institute of Physics.