Open-Framework Germanates and Related Materials

Abstract

Novel open-framework germanates and open low-dimensional structures were synthesized and characterized. Their crystal structures were solved by single crystal X-ray diffraction or X-ray powder diffraction combined with other techniques. Although related open-framework materials, such as zeolites, are of interest for the ability to selectively accommodate guest species in their rings, pores and channels, germanates are primarily of interest for their unique structural properties. Compared to aluminosilicate-based zeolites, germanium oxides readily form frameworks with extra-large rings and low framework density. The formation of elegant germanate architectures is attributed to the unique Ge-O bond geometries compared to Si-O, and the tendency to form large clusters.This thesis is to serve as an introduction to germanate synthesis, structures and characterization. Structures are categorized in accordance to their building units; the Ge7X19 (Ge7), Ge9X25-26 (Ge9) and Ge10X28 (Ge10) (X = O, OH, or F) clusters. Structure determination techniques as well as the characterization techniques used to examine the properties of the materials are presented. While most of the discussed techniques have routinely been used to study crystalline open-frameworks, we introduce the use of infrared spectroscopy for the identification of cluster types, valuable for structure determination by X-ray powder diffraction. Structures and properties of the novel materials ASU-21, SU-62, SU-63, SU-64, SU-65, SU-66, SU-71, SU-72, SU-73, SU-74, SU-75 and SU-JU-14 are described and put into context with previously known structures. The novel structures are all built of the Ge7, Ge9 or Ge10 clusters, and vary from a framework with novel topology to the first open zero-dimensional germanate cavities built of such clusters.