The crystal structure of zeolite barrerite dehydrated in air at 400–450 °C

The crystal structure of the zeolite barrerite dehydrated at 400–450 °C in air (barrerite D of Alberti and Vezzalini [1]) has been solved by X-ray single crystal determination. The cell parameters are a = 12.969(3) Å, b = 16.971(4) Å, c = 16.319(3) Å, vol = 3592(1) Å3, with a volume contraction of 18.9%. By firing, the crystal loses its symmetry centre and the space group changes from Amma (n. 63) to the new A21ma (n. 36). Perpendicular to the b axis, barrerite D is made up of a sequence of zones dense with T(Si/Al) and O atoms which alternate with zones having a low density of these atoms and corresponding to the symmetry plane. Narrow channels are present in the symmetry plane, while cages characteristics of natural barrerite are absent. This is the first occurrence of a dehydrated Si-zeolite with a structure that differs from the original.