Amine-templated open-framework zinc arsenates of varying dimensionalities: synthesis, structure, polymorphism, and transformation reactions

Abstract

Eight new open-framework zinc arsenates, encompassing the entire hierarchy of open-framework structures, have been prepared hydrothermally. The structures include zero-dimensional, one-dimensional chains, two-dimensional layers, and three-dimensional structures formed through the transformation of the molecular zinc arsenates. The structure of [C₆N₄H₂₁] [Zn(HAsO₄)₂(H₂AsO₄)], I, is composed of ZnO₄ and H₂AsO₄ units connected through the vertices forming four-membered rings with HAsO₄ units hanging from the Zn center. The four-membered rings are connected through the corners forming the one-dimensional chain structures in [C₄N₂H₁₂][Zn(HAsO₄)₂]· H₂O, II, and [C₅N₂H₁₄] [Zn(HAsO₄)₂]·H₂O, III. ZnO₄ and AsO₄ units form a fully four-connected two-dimensional structure in [C₄N₂H₁₂] [Zn(AsO₄)]₂, IV. One-dimensional zigzag ladders are connected through HAsO₄ units forming two-dimensional layers in [C₄N₂H₁₂]_1.5 [Zn₂(AsO₄)(HAsO₄)₂]·H₂O, V, while the similar building units form a layer with hanging HAsO₄ units in the layered arsenate [C₆N₄H₂₁]₆[Zn₁₂ (HAsO₄)₂₁], VI. Hanging HAsO₄ units are also observed in the polymorphic structures of [C₆N₃H₂₀] [Zn₂(AsO₄)(HAsO₄)₂]·2H₂O, VII and VIII. Formation of zero-dimensional monomer, I, a fully four-connected layer, IV, and the polymorphic structures, VII and VIII, are important and noteworthy. The transformation reactions of I indicate that the monomer is reactive and gives rise to structures of higher dimensionalities, indicating a possible Aufbau-type building-up process in these structures.