FORTRESS: F block cOvalency and Reactivity defined by sTructural compRESSibility

民用核废料含有来自元素周期表(4f和5f)中f区元素的金属离子自助餐，其中一些使其具有极强的放射性，而且安全处理成本高昂。清理英国的垃圾估计要花费730亿英镑。废物复杂混合物中的大多数f-阻挡离子在物理上非常相似，但它们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，将废物的储存时间从数百万年减少到数千年。目前区分4f(稀土)和5f(超铀)离子的技术状态是，某些离子选择性有机分子在溶液萃取过程中实现了4000倍的显著选择性。然而，不同金属加合物的固态结构显示出金属-配体键长的微小差异，并且目前的4f/5f金属-配体键合的计算机模型不能解释这种选择性。现在，人们提出了多层弱溶剂化相互作用的新的概念上令人愉快的建议，作为区分的原因，但到目前为止，无论是溶液还是固态实验都没有对这些相互作用的作用产生确凿的证据/理解。5f离子中的金属-配体键合被描述为更软的或更共价的，对于负责设计离子选择性有机分子的化学家来说，这表明电子密度的“抹黑”。然而，物理学家对共价性的定义集中在包含重要电子的轨道的能量匹配上，对于在元素周期表的这一部分中共价性实际上意味着什么，存在着很大的争论和困惑。软金属离子也会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无规合作用，是工业上用来生产3000万吨PP PA的锆系催化剂进行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被研究为碳氢化合物的单个C-H键在金属阳离子上断裂的前驱，这是非常可取的烷烃原子经济催化功能化的第一步。用X射线衍射法测定了该化合物晶体的强金属-配位键和弱金属-CH相互作用。在爱丁堡，我们既可以在测量晶体结构时压缩晶体，也可以在压力下从溶液中生长晶体，这会增加溶剂化。人们已经在高压下研究了小分子有机物和鳗系元素合金，并得出了有趣的结果。在这里，我们将首次探索高压对金属-配位键的可压缩性的影响，以及对等结构4f-和5f-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，在德国的欧盟超铀中心，我们还将研究5f系列中较重的成员，例如Np和Pu。我们将结合衍射、光谱学和计算分析(在曼彻斯特)来测量和解释4f离子和5f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，固体表现出不同的可压缩性。我们将把对4f和5f络合物的压力实验与理论相结合，给出一个全新的、概念上简单但严格的定义，定义f-嵌段金属-配体键中的共价度。我们还将关注弱的、无相互作用的相互作用，并在高压(即高溶剂化水平)下生长晶体，以强调4f/5f溶剂化的差异，并提出新的答案来解释核废料萃取剂分子的选择性。最后，我们将利用压力启动晶体内反应，其中弱相互作用可以建立起来，然后被金属破坏，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.