Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, Institut des Sciences Analytiques et de Physico-chimie pour l'Environnement et les Matériaux, CNRS-UPPA-UMR-5254, Hélioparc, 2 Avenue du Président Pierre Angot, 64053 Pau, France.
Phys Chem Chem Phys. 2011 Aug 7;13(29):13222-31. doi: 10.1039/c1cp21012b. Epub 2011 Jun 27.
A novel approach is suggested to investigate the mechanisms of chemical complexation reactions based on the results of Fujii with co-workers; they have experimentally observed that several metals and metalloids demonstrate mass-independent isotope fractionation during the reactions with the DC18C6 crown ether using solvent-solvent extraction. In this manuscript, the isotope fractionation caused by the magnetic isotope effect is used to understand the mechanisms of chemical exchange reactions. Due to the rule that reactions are allowed for certain electron spin states, and forbidden for others, magnetic isotopes show chemical anomalies during these reactions. Mass-independent fractionation is suggested to take place due to the hyperfine interaction of the nuclear spin with the electron spin of the intermediate product. Moreover, the sign of the mass-independent fractionation is found to be dependent on the element and its species, which is also explained by the magnetic isotope effect. For example, highly negative mass-independent isotope fractionation of magnetic isotopes was observed for reactions of DC18C6 with SnCl(2) species and with several Ru(III) chloro-species, and highly positive for reactions of this ether with TeCl(6)(2-), and with several Cd(II) and Pd(II) species. The atomic radius of an element is also a critical parameter for the reaction with crown ether, particularly the element ions with [Kr]4d(n)5s(m) electron shell fits the best with the DC18C6 crown ring. It is demonstrated that the magnetic isotope effect in combination with the theory of orbital hybridization can help to understand the mechanism of complexation reactions. The suggested approach is also applied to explain previously published mass-independent fractionation of Hg isotopes in other types of chemical exchange reactions.
提出了一种新的方法来研究化学络合反应的机制，该方法基于 Fujii 及其同事的研究结果；他们通过溶剂-溶剂萃取实验观察到，在与 DC18C6 冠醚反应时，几种金属和类金属表现出质量独立的同位素分馏。在本文中，利用磁同位素效应引起的同位素分馏来理解化学交换反应的机制。由于反应允许某些电子自旋态发生，而其他自旋态则被禁止，因此磁同位素在这些反应中表现出化学异常。由于核自旋与中间产物的电子自旋的超精细相互作用，导致质量独立分馏发生。此外，发现质量独立分馏的符号取决于元素及其种类，这也可以用磁同位素效应来解释。例如，对于 DC18C6 与 SnCl(2)物种和几种 Ru(III)氯物种的反应，观察到磁性同位素的高度负质量独立同位素分馏，而对于该醚与 TeCl(6)(2-)和几种 Cd(II)和 Pd(II)物种的反应，则观察到高度正质量独立同位素分馏。元素的原子半径也是与冠醚反应的关键参数，特别是具有[Kr]4d(n)5s(m)电子壳层的元素离子与 DC18C6 冠环拟合得最好。证明了磁同位素效应与轨道杂化理论相结合可以帮助理解络合反应的机制。该方法还被应用于解释先前发表的其他类型化学交换反应中 Hg 同位素的质量独立分馏。
