Hydrothermal synthesis of the tin analogue of penkvilksite-2O

The small-pore framework stannosilicate Na₂SnSi₄O₁₁.2H₂O (Sn-AM-3), exhibiting the structure-type of the rare mineral penkvilksite-2O, has been synthesized via a seeded hydrothermal process. The estimated cell dimensions are: a = 16.52, b = 8.80, c = 7.48 Å. The Sn-AM-3 three-dimensional framework is made up of [Si₄O₁₁] silicate sheets interconnected by SnO₆ octahedra. The [Si₄O₁₁] silicate sheets may be described as a combination of the spiral chains formed by the corner-sharing SiO₄ tetrahedra. Sn-AM-3 is the first example of a synthetic microporous stannosilicate whose structure is built up from silicate sheets. All materials were studied by bulk chemical analysis, powder X-ray diffraction, scanning electron microscopy, ²⁹Si, ¹¹⁹Sn, single-and triple-quantum ²³Na magic-angle spinning NMR spectroscopy and thermogravimetry. Solid-state NMR is a particularly powerful technique to establish the presence of the 1M and 2O polytypes and accurately determine their relative abundances in mixed samples.