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

使用金刚石顶锤单元(DAC)对分子固体施加高外压可导致材料结构的巨大变化，例如相变和原子间距离(键长和键角)、分子轨道上的电子分布(例如pi背键合)、氢键相互作用和分子轨道的相对能量经常导致压致变色--压力引起的颜色变化--这是一些压力传感器中使用的现象。通过使用商用DAC，可以在实验室中轻松实现高达约100kbar(约10万大气压)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、穆斯堡尔谱等，方便地监测发生的任何结构变化。在DAC操作中，通过灵敏的螺旋机构将两颗宝石级钻石(约0.6毫米)机械挤压在一起，然后使用光学显微镜将所研究的材料放入一个非常小的孔(直径300微米)，该孔位于两颗钻石之间的薄(300微米)不锈钢垫片的中心。然后，整个手部大小的设备被放置在红外或拉曼微探针光谱仪的显微镜物镜下。我们的高压DAC研究的主要目的是用光谱学的方法研究一系列固体无机材料(例如粘土和其他矿物)、有机材料(例如药物晶型)和有机金属材料在施加和随后释放高压时是否会发生结构变化。在某些情况下，压力的致密化效应可能导致合成全新的材料。在其他方面，可以提取关于化学键相互作用的重要信息。例如，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物质，甚至可能有助于更清楚地了解粘土矿物在触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.