PST-33: A Four-Layer ABC‑6 Zeolite with the Stacking Sequence AABC

The structure model of an ABC-6 family zeolite with the 4-layer stacking sequence AABC was first proposed in 1981, but it has remained undiscovered so far. Here, we report the synthesis of PST-33, which is a small-pore aluminosilicate (Si/Al = 4.1) zeolite with this framework topology, using 5-azonia-spiro[4.4]­nonane ions as an organic structure-directing agent via the so-called multiple inorganic cation approach, and its structure solved by single-crystal X-ray crystallography. PST-33 contains a two-dimensional 8-membered ring pore system consisting of 8-hedral ([4⁶6²]) double 6-ring (d6r), 14-hedral ([4⁶6⁸]) sod, and 17-hedral ([4⁹6⁵8³]) lev cages. The Na⁺ form of PST-33 showed comparable CO₂ adsorption properties to the corresponding cation form of zeolite A and chabazite.