Solving the Hydration Structure of the Heaviest Actinide Aqua Ion Known: The Californium(III) Case
Solving the Hydration Structure of the Heaviest Actinide Aqua Ion Known: The Californium(III) Case
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DOI：
10.1002/anie.200906129
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发表时间：
2010-01-01
影响因子：
16.6
通讯作者：
Marcos, Enrique Sanchez
中科院分区：
文献类型：
--
作者：
Galbis, Elsa;Hernandez-Cobos, Jorge;Marcos, Enrique Sanchez
自从核技术开始以来，锕系元素离子的溶液化学一直是一个基本问题，因为溶剂稳定了锕系元素的高氧化态。[1]开发程序以避免锕系元素从已经积累的核废料迁移到自然水系统是一个非常活跃的领域。[2]锕系元素离子在溶液中的主要性质之一是溶剂化，因为它与络合、沉淀和分解过程密切相关。较重的锕系元素的稀有性和危险性，随着原子序数的急剧增加，阻碍了对沿着该系列的趋势的全面检查，超过了该系列的中间。[3]铥阳离子CmIII通常被认为是最重的锕系元素物种，近年来它引起了实验和理论界的广泛关注。[3，4]对含水三价镧系元素的系统研究揭示了金属-氧距离的收缩和总第一配位数沿着系列的减少。[5]最近的调查，使用扩展X射线吸收精细结构（EXAFS）技术研究，如果这种收缩发生在一个单调的或不规则的方式沿沿着系列。[6]可获得的锕系元素直到Cm III的数据表明类似的收缩，[3，5，7]尽管由于结构数据的不确定性，特别是关于水合数的不确定性，以及关于系列后半部分的信息稀缺，无法给出结论性的答案。在这一系列研究的中间部分，只有一项关于Berkelium（Bk III）的研究报告[8]和一项由我们中的一个人进行的关于californium（III）的初步EXAFS研究。[9]由于CfIII在锕系中的位置，足够精确地测定其配位数和CfO距离，无疑可以阐明锕系收缩的问题。由于这种元素极其稀少，这一目标使这项研究更具基础性而非应用性。具有Cf 3 O键的CfIII的最相似的晶体学数据是Cf（IO 3）3的单晶，其呈现出显著扭曲的三帽三角棱柱，具有宽范围的Cf 3 O距离（2.353-2.921）。[10]这种有限的信息不符合根据常规EXAFS数据分析回答问题所需的准确度。在这里，我们提出了一种替代的方式来研究这种极端的情况下，通过耦合新的高度精细EXAFS数据中获得的锕系元素专用光束线在欧洲同步辐射设施（ESRF，格勒诺布尔），与第一蒙特卡罗（MC）模拟的CfIII在水中。使用了基于从头算量子力学（QM）势能面和可极化和灵活的MCDHO水模型[11]的专门开发的CfOH 2分子间势。图1显示了使用两种模型结构的CfIII水溶液的实验和拟合的k2加权EXAFS光谱，正方形反棱柱构型（SA;见图2a）代表水的八配位。
The solution chemistry of actinide ions has been a fundamental question since the beginning of the nuclear technologies, given that the solvent stabilizes the high oxidation states of actinides.[1] The development of procedures to avoid the migration of actinides from the already accumulated nuclear waste into natural water systems is a field of great activity.[2] One of the primary properties of actinide ions in solution is their solvation, as it is intimately joined to complexation, precipitation, and resolution processes. The rareness and hazardousness of the heavier actinide elements, which steeply increase with the atomic number, has prevented a complete examination of the trends along the series, beyond the middle of the series.[3] The curium cation CmIII has often been considered as the heaviest actinide species characterized, and it has attracted much attention from both experimental and theoretical views in recent years.[3, 4] Systematic studies of the aqueous trivalent lanthanides have revealed a contraction of the metal–oxygen distance and a decrease of the total first coordination number along the series.[5] Recent investigations using extended X-ray absorption fine structure (EXAFS) techniques have examined if this contraction takes place in a monotone or an irregular way along the series.[6] The data available for the actinide series up to CmIII indicates a similar contraction,[3, 5, 7] although a conclusive answer cannot be given owing to the uncertainty of the structural data, particularly concerning the hydration number, and the scarce information on the second half of the series. Beyond the middle of the series, there is only one study reported for berkelium (BkIII)[8] and a preliminary EXAFS study for californium (III) carried out by one of us.[9] Owing to the position of CfIII in the actinide series, an accurate enough determination of the coordination number and CfÀO distance could certainly shed light on the question of the actinide contraction. This objective gives the study a more fundamental than applied character, owing to the extreme rareness of this element. The most similar available crystallographic data of CfIII with CfÀO bonds is that of single crystals of Cf (IO3) 3, which present a significantly distorted tricapped trigonal prism with a wide range of CfÀO distances (2.353–2.921).[10] This limited information does not meet the required level of accuracy for answering the question on the basis of a conventional EXAFS data analysis. Herein we present an alternative way to study this extreme case, by coupling new highly refined EXAFS data obtained in an actinide-dedicated beamline in the European Synchrotron Radiation Facility (ESRF, Grenoble), with the first Monte Carlo (MC) simulations of CfIII in water. Specifically developed CfÀOH2 intermolecular potentials based on ab initio quantum mechanical (QM) potential energy surfaces and the polarizable and flexible MCDHO water model [11] have been used. Figure 1 shows the experimental and fitted k2-weighted EXAFS spectra of a CfIII aqueous solution using two model structures, the square antiprism configuration (SA; see Figure 2a), which represents an octacoordination of water