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

点击翻译按钮获取中文摘要

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.