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

(1)利用带CCD探测器的单晶衍射仪在400K下测量黑绿岩的x射线强度，分析客体分子与二氧化硅框架相互作用的动态性质。指出CCD探测器的测量精度已足够高，但需要更高角度的数据来分析相互作用。(2)分子动力学模拟，在安装了大规模存储器的计算机上进行，未能成功地再现x射线结构、结构变化和变形的细节。(3)尝试水热合成含有CH4、CO2、N2、NO、H2O分子的二氧化硅包合物。成功地合成了黑绿石单晶，并建立了合成细节。(4)实验研究，如x射线衍射研究客体分子和二氧化硅框架之间的相互作用，计划使用高压金刚石砧细胞，以避免在环境条件下的实验中遇到的困难，在这种条件下，不可避免地发生转变和更多的孪晶。这项工作正在进行中。(5)对石英等其他二氧化硅的分子动力学模拟通常是成功的。我们考虑了为什么这种低密度二氧化硅结构的计算失败。毕竟，我们得出的结论是，无论是从实验角度还是从理论角度来看，对原子无序的详细研究都是必不可少的。这类研究对于具有开放结构的硅质钇石有望更容易完成，迄今为止已经积累了大量基于其结构细节的研究。然后我们进行了x射线分析，用CCD探测器和拉曼研究测量了强度。并且发现原子无序运动和声子模式之间有很强的相关性。到目前为止，还没有针对这些硅结构提出基于这种耦合的概念。(6)为了进一步利用计算机模拟技术，我们可能需要更复杂的势能模型来与涉及原子无序的细节进行比较。少

(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