Geometric and topological analysis of zeolite crystal structures by the tiling method: The model of structure of Na,K-paulingite (PAU) Na82K72[Al154Si518O1344] · wH2O

Abstract

Cluster analysis of the crystal structures of paulingite zeolites (Na,Ca0.5,K,K,Ba0.5)10[Al10Si32O84] · 30H2O (PAU, space group Im\(\bar 3\)m) has been performed by the tiling method with the TOPOS program package. The tetrahedral T framework of PAU with 672 tetrahedra in the translated unit cell with a = 35.1 A and V = 43 217 A3 has been completely decomposed into tiles, complementarily connected polycyclic (polyhedral) T clusters. The zeolite structure is represented by an ensemble consisting of nine geometrically different nanoclusters containing 16 to 48 T tetrahedra (the linear dimensions of the nanoclusters are 12 to 18 A, respectively). The nanoclusters correspond to seven topologically different types of tiles: 48T-grc (2a), 32T-pau (12e), 30T-plg (16f), 24T-phi (24h), 20T-gsm (12d), 16T-opr (6b, 12e), and 16T-oto (24h, 48k). In the tiles, the positions occupied by extraframework cations A = Na+/Ca2+ and B = K+/Ba2+ have been determined. The characteristic arrangement of the Na+/Ca2+ cations only at the centers of the 8T rings has been revealed, and for them a new equivalent position in the 16T-opr (6b) tile has been determined. A common crystal-chemical formula of paulingite family zeolites has been obtained: (A,B0.5)154[T672O1344]·wH2O; for the two outermost members, this formula takes the form A154[T672O1344]·wH2O and B77[T672O1344]·wH2O. The composition of the alkaline Na,K-paulingite A154T672O1344·wH2O = Na82K72[Al154Si518O1344] ·wH2O corresponds to the model of a structure with a maximal (100%) and ordered filling of the A cation positions: in the 16T-oto (24h, 48k) tiles for K+ and in the 20T-gsm (12d), 30T-plg (16f), and 16T-opr (6b, 12e) tiles for Na+. Such a distribution and the overall number of Na and K atoms are in good agreement with the data for synthetic paulingite analogues the (Na87K72TEA15)[Al164Si508O1344]·wH2O aluminosilicate and (Na84.5K70.5TEA24.7)[Ga179.7Si492.3O1344]·wH2O gallosilicate.