Probing the chemistry of actinide cation-cation complexes

铀是自然产生的最重的元素，是核废料的主要成分。在空气和环境中，它会形成一种叫做铀酰化合物的二氧化盐，这些二氧化盐都是基于一个带双重电荷的线性O=U=O基团。这些都很容易溶解，是有问题的环境地下水污染物。U=O键在化学上也非常稳定，很少倾向于参与无数的氧基和氧化还原反应，而这些反应是过渡金属氧化物类似物的特征，在生物和工业环境中都有化学和催化用途。铀的人造和高放射性邻居镎也形成线性O=Np=O指示，但由于额外的f电子，表现出更多的氧原子反应性。在核废料中，当氧基团与另一种金属二氧阳离子结合时，阳离子-阳离子复合物就形成了，这使得混合物的行为更难预测，并且表明反应性较低的铀酰化不是较难处理的镎和钚类似物的良好模型。我们最近表明，我们可以“欺骗”铀酰化，使其仅与一个氧原子反应，形成一个强的O-Si共价键，其方式类似于在过渡金属氧化学中看到的。我们已经能够通过将铀酰化结合在一个刚性有机配体框架内，使两个氧原子中的一个暴露在反应中，而另一个在配体框架的腔内仍然无法进入，从而在铀化学中产生这种前所未有的行为。这使得铀酰离子的行为更像海王星离子。在国际电联的欧盟超铀研究联合研究中心工作，我们将把海王星离子放在相同的有机框架中，因为它应该更容易形成O-Si键。这种受控反应将是海王星基离子的一种新型反应。我们将利用刚性配体提供的控制来制造第一个系列的同金属和混合金属双金属，其中两种金属通过中心氧原子通信。再一次，国际电联的工作将使我们能够制造分子，从而易于研究，铀-镎系统。这些新的阳离子-阳离子配合物将帮助我们更好地了解核废料中发现的更复杂的金属氧系统，因此我们将与洛斯阿拉莫斯国家实验室合作获取XAS数据，以确定模型金属-金属距离（来自EXAFS）和共价（来自配体边缘XAS）信息。这些和低氧化态体系的磁性将与国际电联的专家合作进行研究。作为研究人员培训的一部分，还将研究更多的化学深奥项目，例如，我们将使用刚性配体来尝试捕获弯曲铀酰化的第一个例子，以及第一个U=C双键。目前估计清理我们所有核废料的费用是700亿美元（官方核退役管理局的数字），大约96%的乏燃料是可回收的铀。如果我们能更好地了解这种无处不在的二氧化铀的化学性质，它与放射性更强的邻近元素的关系，以及它是如何从环境中沉淀下来的，我们或许能帮助减少英国的核废料。

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 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 oxo-group and redox reactions that are characteristic of transition metal dioxide analogues which have chemical and catalytic uses in both biological and industrial environments. Uranium's man-made and highly radioactive neighbour neptunium also forms linear O=Np=O dications, but due to the extra f-electron, shows much more oxygen atom reactivity. In nuclear waste, cation-cation complexes form when the oxo groups bind to another metal dioxo cation, making the behaviour of the mixtures harder to predict, and suggesting that the less reactive uranyl dication is not a good model for the harder-to-handle neptunium and plutonium analogues.We recently showed that we can 'trick' the uranyl dication into reacting at just one oxygen atom to form a strong O-Si covalent bond, in a manner similar to that seen in transition metal oxo chemistry. We have been able to bring out this unprecedented behaviour in uranium chemistry by binding the uranyl dication within a rigid organic ligand framework which exposes just one of the two oxygen atoms to reactions while the other remains inaccessible within the cavity of the ligand framework. This makes the uranyl ion behave more like the neptunyl ion. Working at the EU Joint research centre for transuranic research at the ITU, we will place the neptunyl ion in the same organic framework, since it should more readily form O-Si bonds. This controlled reaction would be a new type of reactivity for the neptunyl ion. We will use the control afforded by the rigid ligand to make the first series of same- and mixed-metal bimetallics in which the two metals communicate through a central oxo atom. Again, work at the ITU will allow us to make molecular, and thus easy to study, uranium-neptunium systems. These new cation-cation complexes will help us better understand the more complex metal oxo systems found in nuclear wastes, so we will collaborate with Los Alamos National Labs to obtain XAS data to determine model metal-metal distance (from the EXAFS) and covalency (from the ligand edge XAS) information.The magnetism of these, and lower-oxidation state systems will be studied in collaboration with experts at the ITU.As part of the researcher training, more chemically esoteric projects will also be studied, for example, we will use the rigid ligand to try to trap the first example of a bent uranyl dication, and the also first U=C double bond. The current estimated bill for cleaning up all of our nuclear waste is 70 billion (official Nuclear Decommissioning Authority figure), and approximately 96% of used fuel is recyclable uranium. If we can understand better the chemistry of this ubiquitous uranium dioxo dication, how it relates to its more radioactive neighbour elements, and how it is precipitated from the environment, we might be able to help reduce the UK's nuclear waste legacy.