High-pressure spectroscopic studies of solid inorganic, organic and organometallic materials

使用金刚石砧室（DAC）对分子固体施加高外部压力可以导致材料发生巨大的结构变化，例如相变和原子间距离（键长和键角）的变化、分子轨道中的电子分布（例如π背键合）、氢键相互作用以及分子轨道的相对能量，通常会导致压色现象（由压力引起的颜色变化），这是一些压力传感器中采用的现象。通过使用市售的 DAC，可以在实验室中轻松实现高达约 100 kbar（约 100,000 atm）的压力，即接近地质领域，并且随着压力的稳定增加，可以通过各种分子光谱技术（例如红外、拉曼、紫外-可见、发光、穆斯堡尔等）方便地监测发生的任何结构变化。在 DAC 的操作中，两颗宝石级钻石（尖底，约 0.6 毫米）通过敏感的螺旋机构机械挤压在一起，并使用光学显微镜将待研究的材料放入位于两颗钻石之间的薄（300 微米）不锈钢垫圈中心钻的一个非常小的孔（直径 300 微米）中。然后将整个手掌大小的装置放置在红外或拉曼微探针光谱仪的显微镜物镜下。我们高压 DAC 研究的主要目的是通过光谱检查在施加和随后释放高外部压力时是否会在一系列固体无机（例如粘土和其他矿物质）、有机（例如药物多晶型物）和有机金属材料中引起结构变化。在某些情况下，压力的致密化效应可能会导致全新材料的合成。在其他情况下，可以提取有关化学键相互作用的重要信息。例如，针对粘土矿物提出的高压工作可能有助于更清楚地了解地壳和地幔中发生的化学反应，甚至可能有助于更清楚地了解粘土矿物在引发地震中可能发挥的作用。

The application of high external pressures on molecular solids using diamond-anvil cells (DACs) can lead to dramatic structural changes in the materials, e.g., phase transitions and changes in interatomic distances (bond lengths and bond angles), electronic distributions in molecular orbitals (e.g., pi-backbonding), hydrogen bonding interactions, and relative energies of molecular orbitals often leading to piezochromism - color changes induced by pressure - a phenomenon employed in some pressure sensors. By using commercially available DACs, pressures up to about 100 kbar (ca. 100,000 atm), i.e., approaching the geological realm, can readily be achieved in the laboratory and any structural changes occurring can be conveniently monitored by a wide variety of molecular spectroscopic techniques, e.g., infrared, Raman, UV-visible, luminescence, Mossbauer, etc., as the pressure is steadily increased. In the operation of a DAC, two gemstone quality diamonds (culets, ~0.6 mm) are squeezed together mechanically by means of a sensitive screw mechanism and the material under investigation is placed, using an optical microscope, into a very small hole (300-micron diameter) drilled in the centre of a thin (300 micron), stainless-steel gasket located between the two diamonds. The whole hand-sized device is then placed under the microscope objective of an infrared or Raman microprobe spectrometer. The chief aim of our high-pressure DAC research is to examine spectroscopically whether or not structural changes can be induced in a range of solid inorganic (e.g., clays and other minerals), organic (e.g., drug polymorphs) and organometallic materials upon the application and subsequent release of high external pressures. In some cases, the densification effect of pressure may lead to the synthesis of completely new materials. In others, important information about chemical bonding interactions can be extracted. The high-pressure work proposed on clay minerals, for example, may contribute in providing a clearer understanding of the chemistry occurring in the Earth's crust and mantle, and perhaps even what role clay minerals may play in triggering earthquakes.