Open-framework zinc phosphates with unusual architectures

Abstract

Open-framework zinc phosphates, I, [HMTA(H)₃)]₂[Zn₃(PO₄)₂ (HPO₄)₂][(H₂PO₄)₂]·10H₂O, and II [HMTA(H)₃][Zn₂(PO₄) (HPO₄)(H₂PO₄)][(H₂PO₄)], with unusual layered architectures, have been synthesized under ordinary conditions and characterized. The amine phosphate, HMTA-P, also has been synthesized and characterized. The structures of I and II contain strictly alternating ZnO₄, PO₄, H/H₂PO₄ tetrahedral units linked through their vertices forming macroanionic layers with a large interlayer separation of ~20 Å. While I contains the charge compensating amine, the water, and the isolated free H₂PO₄ units in the interlamellar region, II possesses only the amine and the free H₂PO₄ units. In II, one H₂PO₄ units hangs from the layer in a direction perpendicular to the layers. All these structural features have been observed for the first time in open-framework zinc phosphates, in addition to the large interlamellar separation. The structure has extensive O-H...O, N-H...O, C-H...O hydrogen bonds that lend structural stability and support the extra-large separation between the inorganic sheets. The removal of the amine molecules in I and II causes the collapse of the framework forming condensed zinc phosphates. The structural details garnered from this study might be of some use in the design of more complex inorganic systems that involve larger amine molecules, especially for the synthesis of mesoporous solids.