Development of Facilities for Single-Crystal Diffraction at High Pressure on KOALA

固体对压力和温度变化的反应方式揭示了分子间相互作用的本质及其对热力学性质的影响的丰富细节。当对结晶固体施加压力时，它可能会以其环境压力相的压缩形式持续存在，也可能会过渡到一个新相，这为不同类型的分子间相互作用（例如氢键、卤素键、堆叠相互作用）的可变形性和固体中的“能量景观”提供了详细的实验数据。这些信息在有机分子固体中最为重要：制药业每年花费数十亿英镑用于发现新的固体形式，如药物的多晶型和水合物，以及建立模型和了解它们的性质。通过晶体工程设计新的功能分子材料也严重依赖于分子间相互作用的控制。这些结果甚至适用于行星科学，在行星科学中，“分子冰”的热和可压缩性行为为在天体物理环境中模拟沉积物提供了重要的数据：碳是我们银河系中含量第四丰富的元素，人们认为这种元素的最大储存库是多环芳烃。许多种类的分子间相互作用都涉及氢原子：氢键是一个明显的例子，但氢原子在大多数有机分子的外表面占主导地位，它们在色散和静电相互作用中起着重要作用。在这个项目中，我们将探索高压对有机晶体中氢在1 000到10万大气压之间的相互作用的影响。我们将重点关注弱接触的类，这些类越来越多地被调用为指导交互的结构。交互的例子有CH…X ‘氢键’，其中X =卤素，氧或氮，堆叠和CH…多芳烃中的PI相互作用，以及新的相互作用类型，如卤素键、黄素键、烟原键和四元键，它们也被称为结构导向相互作用。将利用单晶和粉末中子衍射研究含有这些相互作用的晶体材料在高压下的响应，并借助于半经验和从头计算数据对结果进行解释。我们方法的一个关键要素将是确定能量、焓、自由能和熵的变化，不仅是计算上的，而且是实验上的，使用我们开发的一种新方法，将可变压力和温度的晶体学数据转换为实验热力学信息。中子衍射对于这项工作是必要的，因为它可以精确地定位h原子，因为中子辐射的穿透性意味着可以在复杂的极端条件环境中获得完整的、高质量的数据。我们的工作也将有助于在中心设施开发新技术和实验方法，与EPSRC优先领域相关，如功能材料和材料表征，研究领域包括分析科学，储能和凝聚态，物理科学和制造未来的主题，以及具有目标特性的扩展材料的定向组装。

The way in which a solid responds to changes in pressure and temperature reveals a wealth of detail about the nature of intermolecular interactions, and their influence on thermodynamic properties. When pressure is applied to a crystalline solid it may persist in a compressed form of its ambient pressure phase or it may undergo a transition to a new phase, providing detailed experimental data on the deformability of different classes of intermolecular interactions (e.g. H-bonds, halogen bonds, stacking interactions) and on 'energy landscapes' in solids. In no area is this information of more importance than in molecular organic solids: the pharmaceutical industry spends billions of pounds per year on discovery of new solid forms such as polymorphs and hydrates of drugs and on modelling and understanding their properties. The design of new functional molecular materials via crystal engineering also depends critically on control of intermolecular interactions. The results are even applicable to planetary sciences, where the thermal and compressibility behaviour of 'molecular ices' yield important data for modelling deposits in astrophysical settings: carbon is the fourth most abundant element in our galaxy, and it is thought that the largest repository for this element is within polycyclic aromatic hydrocarbons. Many classes of intermolecular interaction involve hydrogen atoms: hydrogen bonds are an obvious example, but hydrogen atoms dominate the outer surfaces of most organic molecules and they play an important role in dispersion and electrostatic interactions. In this project we will explore the effect of high pressure on interactions involving hydrogen in organic crystals at pressures between 1 000 and 100 000 atm. We will focus on classes of weak contacts that are increasingly being invoked as structure directing interactions. Examples are interactions such as CH...X 'hydrogen bonds' where X = a halogen, oxygen or nitrogen, stacking and CH...pi interactions which occur in polyaromatic hydrocarbons, and new classes of interaction such as halogen, chalogen, pnictogen and tetrel bonds, which have also been invoked as structure directing interactions. The response of crystalline materials containing these interactions will be studied at high pressure using single crystal and powder neutron diffraction, and the results interpreted with the aid of semi-empirical and ab initio computational data. A key element of our approach will be to determine the changes in energy, enthalpy, free energy and entropy not only computationally but also experimentally, using a new method that we have developed that transforms variable-pressure and temperature crystallographic data into experimental thermodynamic information. Neutron diffraction is necessary for this work because it accurately locates H-atoms and because the penetrating nature of neutron radiation means that complete, high-quality data can be obtained for samples in elaborate extreme conditions environments. Our work, which will also help develop new techniques and experimental methodologies at central facilities, is relevant to EPSRC priority areas such as functional materials and materials characterisation, research areas including analytical science, energy storage and condensed matter, the Physical Sciences and Manufacturing the future themes and to the Directed Assembly of Extended Materials with Targeted Properties grand challenge.