Abella Laura, Philips Adam, Autschbach Jochen
Department of Chemistry , University at Buffalo, State University of New York Buffalo , New York 14260-3000 , United States.
J Phys Chem Lett. 2020 Feb 6;11(3):843-850. doi: 10.1021/acs.jpclett.9b03432. Epub 2020 Jan 21.
Solvated sodium anions (Na) were thought to behave essentially like isolated gas-phase ions that interact only weakly with their environments. For example, Na NMR signals for solvated Na are very sharp, despite the potential for strong quadrupolar broadening. The sharp NMR signals appear to indicate a nearly spherical electron density of the ion. For the present study, ab initio molecular dynamics simulations and quadrupolar relaxation rate calculations were carried out for the Na/Na [2.2.2]cryptand system solvated in methylamine, followed by detailed analyses of the electric field gradient at the sodium nuclei. It is found that Na does not behave like a quasi-free ion interacting only weakly with its environment. Rather, the filled 3s shell of Na interacts weakly with the ion's own core and the nucleus, causing Na to appear in NMR experiments like a free ion.
溶剂化的钠离子（Na⁻）被认为其行为本质上类似于孤立的气相离子，与周围环境的相互作用很弱。例如，尽管存在强烈的四极展宽可能性，但溶剂化Na⁻的Na NMR信号非常尖锐。尖锐的NMR信号似乎表明离子具有近乎球形的电子密度。在本研究中，对溶解在甲胺中的Na⁻/Na [2.2.2]穴状配体体系进行了从头算分子动力学模拟和四极弛豫速率计算，随后详细分析了钠原子核处的电场梯度。结果发现，Na⁻的行为并不像仅与周围环境弱相互作用的准自由离子。相反，Na⁻充满电子的3s壳层与离子自身的核和原子核弱相互作用，导致Na⁻在NMR实验中表现得像一个自由离子。
