Synthesis and single crystal structure refinement of the one-layer hydrate of sodium brittle mica

A sodium brittle mica with the ideal composition [Na4]inter[Mg6]oct[Si4Al4]tetO20F4 was synthesized via melt synthesis in a gas tight crucible. This mica is unusual inasmuch as the known mica structure holds only room for two interlayer cations per unit cell and inasmuch as it readily hydrates despite the high layer charge while ordinary micas and brittle micas are non-swelling. The crystal structure of one-layer hydrate sodium brittle mica was determined and refined from single crystal X-ray data. Interlayer cations reside at the center of the distorted hexagonal cavities and are coordinated by the three inner basal oxygen atoms. The coordination of the interlayer cation is completed by three interlayer water molecules residing at the center of the interlayer region. The relative position of adjacent 2:1-layers thus is fixed by these octahedrally coordinated interlayer cations. Pseudo-symmetry leads to extensive twinning. In total five twin operations generate the same environment for the interlayer species and are energetically degenerate.

The sodium brittle mica has been successfully synthesized by melt synthesis and the crystal structure of the one-layer hydrate of sodium brittle mica was determined from single crystal X-ray diffraction data.Figure optionsDownload as PowerPoint slideHighlights
► Melt synthesis yielded coarse grained sodium brittle mica which showed little disorder.
► Sodium brittle mica hydrated completely to the state of one-layer hydrate.
► Structure of one-layer hydrate of sodium brittle mica could therefore be determined and refined.
► Arrangement of upper and lower tetrahedral sheet encompassing interlayer cation were clarified.