Crystal Structure of the New Layer Silicate RUB-39 and Its Topotactic Condensation to a Microporous Zeolite with Framework Type RRO

Abstract

The new synthetic hydrous layer silicate with code RUB-39, H2[Si18O38]·2(C8H20N)·xH2O, was synthesized from hydrothermal solution after 3 weeks at 150 °C and autogenous pressure. The material crystallized as a colorless, fine-grained powder of sub-micrometer crystallite size. The powder diagram was indexed in the monoclinic space group P2/c with a = 7.33122(5) Å, b = 10.72380(13) Å, c = 17.51354(12) Å, and β = 115.69(6)°. The Rietveld refinement of the crystal structure was refined from laboratory powder X-ray diffraction data based on a structure model derived from the condensation product, zeolite RRO, with final residuals of Rwp = 12.3% and χ2 = 3.1. The silicate layers of the new hydrous layer silicate are known as subunits of the silicate framework of the natural zeolite mineral heulandite and represent a basic construction principle of silicate framework structures. They are interconnected through strong interlayer hydrogen bonds. The remaining residual void space is filled with the organic template cation and hydrate water. The condensation process has been studied with solid-state NMR and differential thermal analysis/thermogravimetric analysis experiments. A mechanism for the condensation is proposed explaining the almost perfect crystallinity of the three-dimensional framework.