Synthesis and Crystal Structure of UiO-16: An Organically Templated Layered Magnesium Phosphate

Abstract

The first organically templated layered magnesium phosphate, [Mg6(H2O)2(PO4)2(HPO4)3H2PO4]-[N2C4H11]+H2O, has been synthesized under hydrothermal conditions and characterized by powder and single-crystal X-ray diffraction, solid-state 31P MAS and CP-MAS NMR spectroscopy, and thermogravimetric analysis. The compound is isostructural with an iron phosphate, [Fe3(HPO4)2(PO4)(H2O)][C4H11N2]0.5, and it crystallizes in the monoclinic space group C2/c with a = 31.076(6) Å, b = 6.3198(13) Å, c = 12.470(3) Å, β = 103.90(3)°, V = 2377.4(8) Å3, and Z = 4. The structure consists of macroanionic sheets of magnesium phosphate separated by piperazinium ions and water molecules. The basic building unit of the inorganic layers is a hexamer of edge-sharing Mg polyhedra. Proton disorder leading to disordered POH and PO functionality in one phosphate tetrahedra was indicated from the X-ray single-crystal solution and confirmed by solid-state NMR spectroscopy.