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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >The structure and bonding of Y, Eu, U, Am and Cm complexes as studied by quantum chemical methods and X-ray crystallography
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The structure and bonding of Y, Eu, U, Am and Cm complexes as studied by quantum chemical methods and X-ray crystallography

机译：量子化学方法和X射线晶体学研究Y，Eu，U，Am和Cm配合物的结构和键合

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Two isomers of Y/Eu(TTA)_3(OH_2) complexes and their structures were identified by single crystal X-ray diffraction, and their geometry and bond distances were also determined using quantum chemical (QM) methods. The data from the two methods agree very well, suggesting that QM is appropriate for calculating structures for which no experimental data are available. This method was therefore used to determine the structures of U/Am/Cm(TTA)_3(OH_2)_2 both in gas phase and in CPCM models of CCl_4, CHCl_3, and H_2O. In these calculations the metal sites were described using the f-in-core approximation, comparing small- and large-core pseudopotentials (SPP and LPP) with their corresponding segmented basis sets. The difference between the Y/Eu-O bond distances between the LPP and SPP is less than 0.02 ?. However, in the actinide complexes the LPP results in larger An-O distances and the difference between the LPP and SPP results decreases from about 0.20 ? in the U-complex to 0.05 ? in the Am- and 0.04 ? in the Cm-complex. The chemical bonding studied by population analysis indicates that there is a significant back bonding in U(TTA)_3(OH_2)_2 from filled orbitals centered on uranium into empty π* orbitals on coordinated oxygen; there is some evidence of back-bonding also in the americium complex, but a significantly smaller effect in the europium and curium species. The relative energy of the two isomers indicates they may be present in solution in comparable amounts, suggesting the possibility of exchange between them. The X-ray structures suggest two exchange pathways, a topological "twist" mechanism and a site exchange involving the opening of a TTA chelate ring.
机译：Y / Eu（TTA）_3（OH_2）配合物的两个异构体及其结构通过单晶X射线衍射鉴定，并使用量子化学（QM）方法确定其几何形状和键距。两种方法的数据非常吻合，这表明质量管理适合计算没有可用实验数据的结构。因此，该方法用于确定气相和CCl_4，CHCl_3和H_2O的CPCM模型中U / Am / Cm（TTA）_3（OH_2）_2的结构。在这些计算中，使用核内f近似描述了金属位点，将小核和大核假电位（SPP和LPP）与其对应的分段基础集进行了比较。 LPP和SPP之间的Y / Eu-O键距离之差小于0.02Ω。然而，在act系元素络合物中，LPP导致较大的An-O距离，并且LPP和SPP结果之间的差从约0.20≤P降低。在U复数中为0.05？在Am-和0.04中？在Cm-complex中。通过种群分析研究的化学键表明，U（TTA）_3（OH_2）_2有明显的反向键，从以铀为中心的填充轨道变为配位氧上的空π*轨道。在complex络合物中也有一些回键的证据，但是对and和cur物种的影响要小得多。两种异构体的相对能量表明它们可能以可比较的量存在于溶液中，表明它们之间可能发生交换。 X射线结构表明存在两种交换途径，一种拓扑“扭曲”机制和涉及TTA螯合环打开的位点交换。

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