Pure silica zeolite-type frameworks: A structural analysis

Since the last major study of silicate crystal structures, many new pure silica zeolite-type frameworks have been discovered. These materials have many interesting properties that are dependent on their structure. We have brought together and analyzed the structures in 35 well-defined frameworks to see how they differ from one another depending on the synthetic route, template, calcination, and composition, and how they differ from the dense silicate phases previously examined. The grand mean values of the Si-O bond distance and the O-Si-O angle are found to be 1.594 angstrom and 109.5 degrees, respectively. The variation and flexibility of the Si-O-Si bond from 133.6 to 180 degrees is discussed, as is the role of fluoride in influencing the O-Si-O bond angles in phases prepared using hydrofluoric acid and ammonium fluoride as mineralizers.