Structure-control of valence electron isomerism in the f-block

金属的价电子排布描述了能与其他元素成键的最高能电子的相对顺序和性质，因此，正是这些电子在很大程度上决定了含金属材料的物理化学性质。对于元素周期表的大部分，一些已知的原理可以指导设计标准，以产生所讨论元素的给定电子构型，并产生理想的特性。金属的氧化态——金属失去的（形式）电子数相对于中性构型，以及结合配体的几何形状是可以控制的两个最重要的特征。该项目旨在发展镧系元素和早期锕系元素（钍、铀、镎、钚）的氧化还原化学，以更深入地了解设计标准，这些标准决定了这些金属在较低氧化状态下的价电子配置。镧系元素和锕系元素（f区）在元素周期表中占据一个位置，金属离子的价电子位于高角度的4f和5f轨道上，这些轨道显示出较差的径向范围，因此这些元素与其他元素之间的成键通常相当弱。正是这些特性产生了这些金属的独特物理特性（例如在磁学和光谱学中的应用）。简单地说，分子中的一个3+金属离子可能有f n个价电子，其中n比中性构型少3个，并且几乎无法改变剩余f电子的化学性质（尽管它们的物理性质可能会改变）。在过去的20年里，f块氧化还原化学的发展已经产生了所有镧系元素（除了Pm），以及钍、铀、镎和钚的2+氧化态的例子，其中许多是第一次。这一显著的进展速度推翻了许多关于这些元素氧化还原特性的先入为主的观念，但也提出了该项目试图解决的问题。对于某些元素，2+离子的价电子排布遵循上面的例子，有n+1个价电子，其中n比中性原子排布小3个。钐、铕和镱就是这样的例子，由于这种行为，它们通常被称为“传统的”2+镧系离子。对于其他元素（如铈），所有分子2+配合物的例子都具有描述为：f n d1的电子构型，其中n仍然比中性原子构型小3，并且一个电子位于d轨道上（对于铈2+:f1 d1）。由于d轨道与f轨道（更大的径向范围，更分散，不同的磁性）有本质上的不同，2+铈分子（有两个金属价电子- f1 d1）的物理化学性质应该与3+镨分子（也有两个金属价电子- f2）有本质上的不同。一些元素，如铀，已经被证明在2+氧化态下可以容纳两种类型的电子构型：fn +1和fn d1。驱动一种构型优于另一种构型的潜在性质鲜为人知，并且是合成化学前沿的一个未被探索的主题。该项目将在金属2+化合物的f区产生样品，确定它们的价电子构型，并使用磁和光谱技术的结合来确定指导特定构型形成和稳定性的性质。这些结果将应用于自旋电子学和量子技术领域，这些领域依赖于通过开发巨大分子自旋的新途径来控制自旋，并在f位配位化学方面取得根本性进展，为其反应性的未来进展奠定基础。

The valence electron configuration of a metal describes the relative ordering and properties of the highest-energy electrons - those that are available for bonding with other elements, and thus it is these which largely dictate the physicochemical properties of metal-containing materials. For much of the Periodic Table, some known principles can guide the design criteria needed to produce a given electron configuration of the element in question and result in desirable properties. The oxidation state of the metal - the (formal) number of electrons the metal has lost versus the neutral configuration, and the geometry of bound ligands are two of the most important features which can be controlled. This project seeks to develop the redox chemistry of the lanthanides, and early actinide (thorium, uranium, neptunium, plutonium) elements towards a deeper understanding of the design criteria which dictate the valence electron configurations of these metals in lower oxidation states.Lanthanide and actinide elements (the f-block) occupy a position in the Periodic Table where the valence electrons in metal ions reside in highly angular 4f- and 5f-orbitals, which show poor radial extent and thus the bonding between these elements and others is typically quite weak. It is these characteristics which engender the unique physical properties typical of these metals (e.g. applications in magnetism and optical spectroscopy). Simply, a 3+ metal ion in a molecule may have f n valence electrons, where n is three less than the neutral configuration, and there is little which may be done to change the chemical properties of the remaining f-electrons substantially (though their physics may be altered).Developments the chemistry of f-block redox chemistry over the last 20 years have produced examples of all the lanthanides (except Pm), as well as thorium, uranium, neptunium, and plutonium in the 2+ oxidation state, many of these for the first time. This remarkable pace of advancement has overturned many preconceptions about the redox properties of these elements, but has raised questions that this project seeks to address.For some elements, the valence electron configuration of 2+ ions follows the example above with f n+1 valence electrons where n is three less than the neutral atomic configuration. Samarium, europium and ytterbium are examples of this and are often termed "traditional" 2+ lanthanide ions due to this behaviour. For other elements (such as cerium), all examples of molecular 2+ complexes feature an electron configuration described as: f n d1, where n is still three less than the neutral atomic configuration, and one electron resides in a d-orbital (for cerium 2+: f1 d1). As d-orbitals are fundamentally different to f-orbitals (larger radial extent, more diffuse, different magnetic properties), the physicochemical properties of cerium 2+ molecules (which have two metal valence electrons - f1 d1), should differ substantially from molecules with praseodymium 3+ which also features two metal valence electrons (f2). Some elements such as uranium have been shown to accommodate both types of electron configuration in the 2+ oxidation state: f n+1, and also f n d1. The underlying properties which drive the preference for one configuration over the other are poorly known, and is an under explored topic at the forefront of synthetic chemistry.This project will produce examples across the f-block of metal 2+ compounds, determine their valence electron configurations, and use a combination of magnetic and spectroscopic techniques to identify the properties which direct the formation and stability of specific configurations. These results will have applications in the fields of spintronics and quantum technologies which rely on the control of spins by developing new routes to giant molecular spins, and produce fundamental advances in f-block coordination chemistry foundational to future advances in their reactivities.