FORTRESS: F block cOvalency and Reactivity defined by sTructural compRESSibility

民用核废料中含有大量来自元素周期表f区（4f和5 f）的金属离子，其中一些使其具有极强的放射性，安全处理成本高昂。清理英国的废物估计需要730亿英镑。废物复杂混合物中的大多数f区离子在物理上非常相似，但它们的电子密度分布的细微差异应该能够使最危险的离子被分离和钝化，从而将废物存储时间从数百万年缩短到数千年。区分4f（镧系元素）与5 f（超铀锕系元素）离子的现有技术是在溶液萃取过程中通过某些离子选择性有机分子实现的显著的4000倍选择性。然而，不同金属加合物的固态结构在金属-配体键距离上显示出极小的差异，并且目前的4f/5 f金属-配体键合的计算机模型不能解释选择性。新的，概念上令人满意的建议，多层弱溶剂化相互作用，现在建议的原因分化，但到目前为止，无论是溶液或固态实验都没有产生决定性的证据/理解这些相互作用的作用。在5 f离子中的金属配体键合被描述为“软”或更共价，对于负责设计离子选择性有机分子的化学家来说，这意味着电子密度的“模糊”。然而，物理学家对共价的定义集中在包含重要电子的轨道能量的匹配上，并且对于共价在元素周期表的这一部分中的实际含义有很多争论和混乱。软金属离子也与溶剂形成更弱的相互作用。金属碳氢化合物的弱相互作用被称为“agostic”，是工业上用于生产3000万吨聚丙烯的锆催化剂对丙烯聚合的立体化学控制的关键。这种弱相互作用也在实验室中作为烃的单个C-H键在金属阳离子上裂解的前体进行了研究，这是烷烃高度理想的原子经济型催化官能化的第一步。强的金属-配体键和弱的金属-CH相互作用都可以使用化合物晶体上的X射线衍射来测量。在爱丁堡，我们既可以在测量晶体结构时压缩晶体，又可以在压力下从溶液中生长晶体，从而增加溶剂化。小的有机物和锕系合金已经在高压下进行了研究，并得到了有趣的结果。在这里，我们将首次探讨高压对金属-配体键的可压缩性和对同构4f-和5 f-嵌段分子中与溶剂/配体外围基团的弱相互作用的影响。在爱丁堡，我们将重点研究铀，在德国的欧盟超铀元素中心，我们还将研究5 f系列中较重的元素，例如镎和钚。我们将结合联合收割机衍射，光谱学和计算（在曼彻斯特）分析来测量和解释4f-和5 f-离子之间的差异。我们将集中讨论强共价键的可压缩性。根据共价程度的不同，固体显示出不同的压缩性。我们将结合联合收割机对4f和5 f配合物的压力实验和理论，对f区金属-配体键中备受争议的共价度给出一个全新的、概念上简单但严格的定义。我们还将关注弱的、agostic的相互作用，在高压下生长晶体（即高溶剂化水平），以强调4f/5 f溶剂化差异，并提出新的答案来解释核废料提取剂分子的选择性。我们将利用压力来启动晶体内的反应，在这种反应中，弱相互作用可以建立起来，然后被金属打破，目标是一些非常不寻常的新分子。

Civil nuclear waste contains a smorgasbord of metal ions from the elements in the f-block of the periodic table (the 4f and 5f), some of which render it extremely radioactive, and costly to handle safely. Clean-up of the UK's waste carries an estimated £73 bn price tag. Most f-block ions in the waste's complex mixture are physically very similar, but subtle differences in their electron density distribution should enable the most dangerous ions to be separated and passified, reducing waste storage times from millions to thousands of years. The state of the art for differentiation of the 4f (lanthanide) from the 5f (transuranic actinide) ions is the remarkable 4000-fold selectivity achieved by certain ion-selective organic molecules in solution extraction processes. However, solid-state structures of the different metal adducts show minimal differences in metal-ligand bond distances, and the current computer models of the 4f/5f metal-ligand bonding cannot explain the selectivity. New, conceptually pleasing proposals of multiple layers of weak solvation interactions are now suggested as the reason for differentiation but, as yet, neither solution nor solid state experiments have produced conclusive evidence/understanding of the role of these interactions.The metal-ligand bonding in 5f ions is described as 'softer' or more covalent, which to the chemist tasked with designing the ion-selective organic molecules suggests a 'smearing out' of the electron density. However, the physicists' definition of covalency centres on the matching of the energy of the orbitals which contain the important electrons, and there is much debate and confusion as to what covalency actually means in this part of the periodic table. Soft metal ions also form more weak interactions with solvents. Metal hydrocarbon weak interactions are called 'agostic' and are key to the stereochemical control of polymerisation of propene by zirconium catalysts used by industry to make 30 million tons of polypropylene pa. Such weak interactions are also studied in the lab as the precursor to the cleavage of a single C-H bond of a hydrocarbon across a metal cation, the first step in the highly desirable atom-economical catalytic functionalisation of alkanes. Both the strong metal-ligand bonds, and weak metal-CH interactions can been measured using X-ray diffraction on crystals of the compound. At Edinburgh we can both compress the crystals as their structures are measured, and grow the crystals from solution at pressure, which increases solvation. Small organics and actinide alloys have already been studied at high pressure, with interesting results. Here, we will explore for the first time the effect of high pressures on the compressibility of metal-ligand bonds and on weak interactions with solvent/ligand peripheral groups in isostructural 4f- and 5f-block molecules. In Edinburgh we will focus on uranium, and at the EU centre for transuranics in Germany we will also study heavier members of the 5f series, e.g. neptunium and plutonium. We will combine diffraction, spectroscopy, and computational (at Manchester) analyses to measure and interpret the differences between the 4f- and 5f-ions. We will focus on the compressibility of the strong, 'covalent' bond. Solids show different compressibility depending on the extent of covalency. We will combine pressure experiments on 4f and 5f complexes with theory to produce a completely new and conceptually simple yet rigorous definition of the much-debated degree of covalency in the f-block metal-ligand bond.We will also focus on weak, agostic interactions, and grow crystals at high pressure (i.e. high solvation levels) to accentuate the 4f/5f solvation differences and propose new answers to explain the selectivity of nuclear waste extractant molecules.Finally, we will use pressure to initiate in-crystal reactions where weak interactions can be set up then broken by the metal, targeting some very unusual new molecules.