Actinide Polyoxo Chemistry

锕系多氧化学

基本信息

批准号：
EP/M010554/1
负责人：
Polly Arnold
金额：
$ 75.86万
依托单位：
University of Edinburgh
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2014
资助国家：
英国
起止时间：
2014 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FM010554%2F1
关键词：
Actinide Polyoxo Chemistry

项目摘要

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).

铀是最自然发生的元素，是核废料的主要组成部分。在空气和环境中，它形成称为铀酰化合物的二氧化盐，它们都基于双电荷，线性o = u = o组。这些化合物非常可溶，是有问题的环境地下水污染物。 U = O键在化学上也非常健壮，几乎没有参与多种反应的倾向，这些反应是过渡金属二氧化金属类似物的特征，这些反应在生物和工业环境中具有化学和催化用途。由于相对论的影响，thor，核废料的另一个组成部分以及由于较低的增殖风险而产生的潜在核燃料，也没有直接，可预测的化学反应，并且是一种非常柔软的+4金属离子。尽管诱人的瞥见可能来自气相研究，但其分子氧化物的行为尚不清楚，这表明氧结构完全不同于其他乙酰基离子。铀的人造和高放射性的邻居neptunium形成线性o = np = o等铀，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Oxo基团与另一种金属二氧阳离子结合时，与U，NP和PU形成了阳离子阳离子复合物，使混合物的行为更难预测。但是，通过将电子添加到铀酰离子中，我们和其他人近年来表明，单一降低的铀酰可以为较重的脱乙酰基提供更氧气反应性，更好的模型。由于从地下水中沉淀铀的途径涉及最初的单电子还原至水溶液中间体，因此这些稳定的U（V）铀酰配合物是了解如何沉淀铀的潜在重要模型。我们发现与过渡金属氧化学相似的肌动蛋白离子反应性的工作重点是使用刚性有机配体框架暴露其中一种氧原子。我们最近报道了一个较小，更受限的大环，可以结合一个或两个铀或th阳离子，迄今为止，在较低的氧化状态下。这也使我们能够查看金属配体和金属金属相互作用的共价。我们将使用这两种刚性配体提供的控制，以制造一系列具有新几何形状的actinide oxo络合物。一些最初预计包括更深奥的项目在内的一些项目纯粹是学术兴趣，也是研究人员培训的重要组成部分。其中一些反应将与环境和废物相关的分子过程有更多相关性，包括质子，电子和Oxo组重排，转移和抽象。关于这些新复合物的反应性的结果将有助于我们更好地了解核废料中发现的更复杂的金属氧系统和环境。我们将通过最具反应性的actacinide oxo络合物来查看碳氢化合物C-H键裂解，从而在纯净的水合碳底物上起作用，但认识到与有机污染物造成的有机污染物造成的光粒毒品分解的相关性。在ITU（Karlsruhe）的欧盟透明研究中心工作中心，我们还将研究这些复合物的Neptunium类似物。这些系统的分子性也将使单层和双金属配合物的磁性比固态化合物更容易理解和建模。 ITU的专家将能够确定两种金属是否通过中央的Oxo原子或什至通过配体Pi-Systems进行通信。我们还将向INE（核废料处置研究所），Karlsruhe和Los Alamos National Labs的合作者提供样品，以获取XAS数据，以研究价值轨道，金属 - 金属距离/相互作用（来自EXAFS）和共和性（来自Ligand Edge Xas）。