Understanding lanthanoid(III) hydration structure and kinetics by insights from energies and wave functions.
Understanding lanthanoid(III) hydration structure and kinetics by insights from energies and wave functions.
复制标题
DOI：
10.1021/ic500991x
复制
发表时间：
2014-06
影响因子：
4.6
通讯作者：
Jun Zhang;Norah Heinz;M. Dolg
中科院分区：
文献类型：
--
作者：
Jun Zhang;Norah Heinz;M. Dolg
从能量和波函数两个方面对镧系元素三价离子的水合作用进行了理论研究。在增量方案的帮助下，首次在CCSD（T）水平上使用大基组计算了镧系元素（III）水配合物。这些计算证明，SCS-MP2是几乎一样准确的CCSD，从而使我们能够给出最准确的第一原理水合吉布斯自由能和可靠的首选配位数（CN）的镧系元素（III）水配合物：9，8，和两者，分别为轻，重，和中间镧系元素。通过一系列波函数分析，探讨了特定氯化萘优先选择的深层次原因。一个意想不到的观察是，随着Ln从钐到镥，九水镧系元素配合物中的Ln-O键变得更弱，而它们变得更短。因此，由于封端Ln-O键变得更容易破坏，较重的镧系元素将优选低CN，即，8.在此基础上和以前的工作的其他小组，镧系元素（III）离子的水交换动力学模型的建议。该模型表明，中间镧系元素中出现的中等强度的封端Ln-O键有利于在水交换过程中形成双帽三角棱镜中间体。这解释了一些核磁共振实验，更重要的是，一个观察，困惑了研究人员很长一段时间，即，在镧系元素的中间区域，交换速率达到最大值，但在镧系元素的开始和结束处，交换速率较低。这种非平凡的行为的上限Ln-O键的解释，并认为确定镧系元素（III）离子的水合行为。
The hydration of all trivalent lanthanoid (Ln) ions is studied theoretically from two aspects: energy and wave function. With the help of the incremental scheme, for the first time the lanthanoid(III) aqua complexes are computed at the CCSD(T) level using large basis sets. These computations prove that SCS-MP2 is nearly as accurate as CCSD, thus enabling us to give the most accurate first principle hydration Gibbs free energies and reliable preferred coordination numbers (CNs) of lanthanoid(III) aqua complexes: 9, 8, and both, for light, heavy, and intermediate lanthanoids, respectively. Then a series of wave function analyses were performed to explore the deeper reasons for the preference of specific CNs. An unexpected observation is that as Ln goes from samarium to lutetium, the capping Ln-O bonds in nona-aqua lanthanoid complexes become weaker while they get shorter. Therefore, as the capping Ln-O bonds are getting easier to disrupt, heavier lanthanoids will prefer a low CN, i.e., 8. On the basis of this and previous work of other groups, a model for the water exchange kinetics of lanthanoid(III) ions is proposed. This model suggests that the capping Ln-O bonds of moderate strength, which occur for intermediate lanthanoids, are advantageous for the formation of a bicapped trigonal prism intermediate during water exchange. This explains some NMR experiments and, more importantly, an observation which puzzled investigators for a long time, i.e., that the exchange rate reaches a maximum for the middle region but is low at the beginning and end of the lanthanoid series. This nontrivial behavior of capping Ln-O bonds is interpreted and is believed to determine the hydration behavior of lanthanoid(III) ions.