Diffraction for chemical reactions: gas uptake and extrusion in non-porous crystals

虽然多孔固体对气体的吸收或释放已经得到了很好的证实，甚至可以在这些过程中发生在保持结晶的材料中，但类似的气体在非多孔晶体材料中的吸收和释放是非常罕见的，而且对其知之甚少。当然，这意味着在分子紧密聚集在一起的固体中，为了允许小分子从气相进入，或者在被困的情况下被释放，需要显著的灵活性。拟议的项目建立在初步结果的基础上，为三种能够吸收或释放小分子（如卤化氢、分子碘或醇）的晶体材料家族提供了概念验证。这些过程实际上是化学反应，在大多数情况下需要共价键和结晶固体内部分子几何结构的重大变化。尽管这些分子的运动和强键的形成或断裂，这些材料家族仍然保持着它们的结晶性。这使得它们非常适合通过衍射方法进行研究，衍射方法可以提供晶体内分子结构的详细几何信息。特别是将使用同步加速器x射线辐射，采用单晶和粉末衍射的方法来绘制这些反应的进展图，并对每种材料进行系统研究，从而揭示这些不寻常反应的机理细节。这些实验将与红外光谱测量相结合，红外光谱测量可用于监测气体和单晶中子衍射，单晶中子衍射将用于在氢原子在反应中起关键作用的情况下从晶体中获得特别精确的几何形状。这些结果将对理解分子材料的行为，特别是它们经历动态行为甚至化学反应的能力具有重要的基础意义。这对从事分子材料设计的众多科学家来说是有价值的。所研究的反应也被认为与分子晶体的水合/脱水等过程有关，这对制药工业具有很大的商业利益，制药工业以晶体形式配制许多药物，其功效在很大程度上取决于特定的晶体形式。

Although uptake or release of gases by porous solids is well established and can even occur in materials that remain crystalline during such processes, analogous uptake and release of gases by non-porous crystalline materials is very rare and extremely poorly understood. The implication, of course, is that significant flexibility is required within a solid where molecules are tightly packed together in order to permit even small molecules to enter from the gas phase, or to be released if trapped.The proposed project builds upon preliminary results that provide a proof-of-concept for three families of crystalline materials that are able to either absorb or release small molecules such as hydrogen halides, molecular iodine or alcohols. These processes are in fact chemical reactions that require in most instances major changes in covalent bonding and in molecular geometry within the crystalline solid. Despite these movements of molecules and the formation or breaking of strong bonds, these families of materials retain their crystallinity. This makes them ideal for study by diffraction methods, which can provide detailed geometric information on the molecular structures within the crystals. In particular synchrotron X-ray radiation will be used, employing the methods of single crystal and powder diffraction to chart the progress of these reactions and to conduct systematic studies within each family of materials that will permit details of the mechanism of these unusual reactions to be revealed. These experiments will be combined with infra red spectroscopic measurements that can be used to monitor the gases and single crystal neutron diffraction which will be used to obtain particularly accurate geometries from crystals in cases where hydrogen atoms play a key role in the reactions. The results will be of great fundamental importance in understanding the behaviour of molecular materials, specifically their ability to undergo dynamic behaviour and even chemical reactions. This will be of value to a wide range of scientists engaged in designing molecular materials. The reactions studied are also believed to be related to processes such a hydration/dehydration of molecular crystals which are of great commercial interest to the pharmaceutical industry which formulates many drugs in crystalline form and for which efficacy can depend greatly on the particular crystalline form.