Synthesis and Characterization of a New Family of Thermally Stable Open-Framework Zincophosphate/Arsenate Phases: M3Zn4O(XO4)3·nH2O (M = Na, K, Rb, Li, ...; X = P, As; n = ∼3.5−6). Crystal Structures of Rb3Zn4O(PO4)3·3.5H2O, K3Zn4O(AsO4)3·4H2O, and Na3Zn4O(PO4)3·6H2O

The syntheses, representative crystal structures, and some properties of a new family of microporous zincophosphate/arsenate materials, denoted M3Zn4O(XO4)3·nH2O (M = Li, Na, K, Rb, Cs, ...; X = P, As; n = ∼3.5−6), are reported. All these materials are based on a flexible, anionic Zn4O(XO4)3 network built up from vertex-linked tetrahedral ZnO4 and XO4 units. Four ZnO4 units share a vertex, resulting in novel OZn4 centers. The use of mixed four-coordinate anion types (XO43-, O2-) results in a number of interesting structural and stability properties. The M3Zn4O(XO4)3·nH2O network contains only pairs of 3-rings (a spiro-5 unit) and 8-rings, and no 4-rings or 6-rings: it encloses roughly spherical cavities connected by a three-dimensional network of 8-ring channels propagating in the orthogonal [100], [010], and [001] directions (cubic unit-cell axes). Extraframework cations and water molecules occupy these cavities and channels. These phases display typical “zeolitic” dehydration/rehydration and ion-exchang...