Crystal structures of silica clathrate compounds and absorption mechanism of guest molecules

点击翻译按钮获取中文摘要

(1)X-ray intensities of melanophlogite were measured at 400K on a single crystal diffractometer with CCD detector to analyze dynamic nature of interactions betweenguest molecules and silica frameworks. It is suggested that CCD detector is accurate enough, but higher angle data are necessary for analyzing the interactions.(2)Molecular dynamics simulation, performed with a computer installed with large scale memories, did not succeed to reproduce the X-ray structures, structural changes and deformations in details.(3)Hydrothermal syntheses of silica clathrates containing CH4,CO2,N2,NO,H2O molecules were attempted. Melanophlogite single crystals were successfully synthesized and the details of syntheses were established.(4)Experimental studies such as X-ray diffractions to investigate interactions between guest molecules and silica frameworks were planned for the use of high pressure diamond anvil cell to avoid difficulties encountered in experiments at ambient conditions, where transform … More ation twinning is inevitable. This is under progress.(5)Molecular dynamics simulations for other silicas like quartz are usually successful. We considered why the calculations failed for such low-density silica-structures. After all we arrived at a conclusion that detailed studies about atomic disorder are essentially necessary for either experimental or theoretical point of view. This type of study is expected to be done more easily for tridymite, a silica with an open structure, on which structural details based on a large numbers of studies have been accumulated so far. We then performed X-ray analyses with intensities measured with a CCD detector and Raman studies. and found strong correlations between atom disordering motions and phonon modes. No concept based on this type of coupling has been proposed for these silica structures so far.(6)To go further with the computer simulation technique, we may need more sophisticated potential energy models to compare with the details involving atom disorder. Less