K0.72Na1.71Ca5.79Si6O19 – the first oligosilicate based on [Si6O19]-hexamers and its stability compared to cyclosilicates
V. Kahlenberg, H. Krüger, S. Garber, B. Krüger, E. Libowitzky, S. Kröll, T. S. Hofer, J. M. Gallmetzer and F. R. S. Purtscher
Cover illustration: Topologically distinct polyhedral micro-ensembles (PMEs) in the crystal structure of a potassium calcium silicate representing the first known compound containing [Si6O19]-oligomers. The crystal structure can also be described as a mixed tetrahedral-octahedral framework, based on corner-sharing [SiO4]- and [CaO6]-units. On the lowest sublevel, the PMEs are formed for each octahedron and tetrahedron in the asymmetric unit by considering all directly bonded [CaO6]- and [SiO4]-groups. They represent a geometrical interpretation of the coordination sequences up to the index k = 3. See Kahlenberg et al. [Acta Cryst. (2024), B80, 474–487].
