Actinide Polyoxo Chemistry

铀是最重的天然元素，也是核废料的主要成分。在空气和环境中，它形成称为铀酰化合物的二氧化物盐，这些化合物都是基于双电荷的线性O=U=O基团。这些化合物是非常可溶的，是有问题的环境地下水污染物。U=O键在化学上也非常坚固，并且几乎没有参与过渡金属二氧化物类似物特有的无数反应的倾向，过渡金属二氧化物类似物在生物和工业环境中具有化学和催化用途。由于相对论效应，钍，核废料的另一种成分，以及由于较低的扩散风险而感兴趣的潜在核燃料，也不具有直接的，可预测的化学性质，并且是非常软的+4金属离子。其分子氧化物的行为知之甚少，尽管来自气相研究的诱人一瞥可能是什么，表明氧代结构完全不同于其他actinyl离子。铀的人造和高放射性邻居镎与铀一样形成线性O=Np=O，但由于额外的f-电子，显示出更多的氧原子反应性。在核废料中，当氧代基团与另一种金属二氧代阳离子结合时，会与U、Np和Pu形成阳离子-阳离子复合物，使得混合物的行为更难预测。然而，通过给铀酰离子添加一个电子，我们和其他人近年来已经证明，单一还原的铀酰可以为更重的actinyls提供更好的氧反应模型。由于从地下水中沉淀铀的途径涉及初始的单电子还原为水不稳定的中间体，这些稳定的U（V）铀酰络合物是理解铀沉淀的潜在重要模型。我们的工作，以揭示类似于过渡金属含氧化学中所看到的锕系离子的反应性，集中在使用一个刚性的有机配体框架，以暴露一个氧原子。我们最近报道了一个更小，更受约束的大环，可以结合一个或两个铀或钍阳离子，到目前为止，在较低的氧化态。这也使我们能够观察金属-配体和金属-金属相互作用中的共价性。我们将使用这两个刚性配体提供的控制，使一系列的锕系氧配合物与新的几何形状。有些项目，包括更深奥的化学项目，最初预计纯粹是学术兴趣，是研究人员培训的重要组成部分。一些反应将与环境和废物相关的分子过程更相关，包括质子，电子和氧代基团重排，转移和提取。有关这些新的配合物的反应性的结果将帮助我们更好地了解更复杂的金属氧合系统中发现的核废料和environment.We将看看碳氢化合物的C-H键裂解的最活跃的锕系氧合配合物，工作在纯碳氢化合物基板，但认识到的相关性，由铀酰的光解引起的有机污染物的破坏。在ITU（卡尔斯鲁厄）的欧盟超铀研究联合研究中心工作，我们还将研究这些络合物的镎类似物。这些系统的分子性也将使单和双络合物的磁性比固态化合物更容易理解和建模。ITU的专家将能够确定这两种金属是否通过中心氧原子甚至通过配体π系统进行通信。我们还将向INE（核废料处理研究所）、卡尔斯鲁厄和美国洛斯阿拉莫斯国家实验室的合作者提供样品，以获得XAS数据，从而可以研究价轨道、金属-金属距离/相互作用（来自EXAFS）和共价性（来自配体边缘XAS）。

Uranium, the heaviest naturally occurring element, is the main component of nuclear waste. In air, and in the environment, it forms dioxide salts called uranyl compounds, which are all based around a doubly charged, linear O=U=O group. These compounds are very soluble and are problematic environmental groundwater contaminants. The U=O bonds are also extraordinarily chemically robust and show little propensity to participate in the myriad of reactions that are characteristic of transition metal dioxide analogues which have chemical and catalytic uses in both biological and industrial environments. Due to relativistic effects, thorium, another component of nuclear waste, and a potential nuclear fuel of interest due to the lower proliferation risk, also does not have straightforward, predictable chemistry, and is a remarkably soft +4 metal ion. The behaviour of its molecular oxides is poorly understood, although tantalising glimpses of what might be possible come from gas phase studies that suggest oxo structures completely unlike the other actinyl ions. Uranium's man-made and highly radioactive neighbour neptunium forms linear O=Np=O dications like uranium, but due to the extra f-electron, shows much more oxygen atom reactivity. In nuclear waste, cation-cation complexes form with U, Np, and Pu when the oxo groups bind to another metal dioxo cation, making the behaviour of the mixtures harder to predict. However, by adding an electron to the uranyl ion, we and others have shown in recent years that the singly reduced uranyl can provide a more oxo-reactive, better model for the heavier actinyls. Since the route for precipitating uranium from groundwater involves an initial one-electron reduction to an aqueous-unstable intermediate, these stable U(V) uranyl complexes are potentially important models for understanding how uranium is precipitated. Our work to uncover actinyl ion reactivity similar to that seen in transition metal oxo chemistry has focused on using a rigid organic ligand framework to expose one of the oxygen atoms. We have most recently reported a smaller, more constrained macrocycle that can bind one or two uranium or thorium cations, so far in the lower oxidation states. This also allowed us to look at covalency in the metal-ligand and metal-metal interactions. We will use the control afforded by these two rigid ligands to make a series of actinide oxo complexes with new geometries. Some, including more chemically esoteric projects, are initially anticipated to be purely of academic interest, and an important part of researcher training. Some of the reactions will have more relevance to environmental and waste-related molecular processes, including proton, electron, and oxo group rearrangement, transfer, and abstraction. Results concerning the reactivity of these new complexes will help us better understand the more complex metal oxo systems found in nuclear wastes and the environment.We will look at hydrocarbon C-H bond cleavage by the most reactive actinide oxo complexes, working on pure hydrocarbon substrates, but recognising the relevance to the destruction of organic pollutants induced by photolysis of uranyl. Working at the EU Joint research centre for transuranic research at the ITU (Karlsruhe), we will also study the neptunium analogues of these complexes. The molecularity of these systems will also make the magnetism of mono- and bimetallic complexes easier to understand and model than solid-state compounds. The experts at the ITU will be able to identify whether the two metals communicate through a central oxo atom or even through ligand pi-systems. We will also provide samples to collaborators at the INE (institute of nuclear waste disposal), Karlsruhe and Los Alamos National Labs, USA, to obtain XAS data that allow the study of the valence orbitals, metal-metal distances/interactions (from the EXAFS) and covalency (from the ligand edge XAS).