Synthesis and Characterization of Three Novel Cation-Containing\n(NH₄⁺/C₃H₇NH₃⁺/NH₃⁺C₂H₄NH₃⁺) Aluminum Diphosphonates

Abstract

Three new aluminum diphosphonates (C₃H₇NH₃){AlF[(HO)O₂PC₂H₄PO₃]} (<b>1</b>) (orthorhombic, <i>Pnma</i>, <i>a</i> = 8.2048(1)\nÅ, <i>b</i> = 6.90056(6) Å, <i>c</i> = 19.6598(4) Å, <i>Z</i> = 4), (H₃NC₂H₄NH₃)[Al(OH)(O₃PC₂H₄PO₃)] (<b>2</b>) (monoclinic, <i>P</i>2₁<i>/n</i>, <i>a</i> =\n11.142(3) Å, <i>b</i> = 7.008(2) Å, <i>c</i> = 12.903(5) Å, β = 96.24(7)°, <i>Z</i> = 4), and (NH₄)₂[AlF(O₃PCH₂PO₃)] (<b>3</b>) (orthorhombic,\n<i>Cmcm</i>, <i>a</i> = 16.592(2) Å, <i>b</i> = 7.5106(9) Å, <i>c</i> = 7.0021(9) Å, <i>Z</i> = 4) have been synthesized by solvothermal\nmethods in the presence of linear organic ammonium cations (for <b>1</b> and <b>2</b><b>)</b> and ammonium cations (for <b>3</b>) and their\nstructures determined using powder, microcrystal, and single-crystal X-ray diffraction data, respectively. All three\nmaterials contain a similar one-dimensional chain motif which is related to that found in the mineral Tancoite. This\nchain motif consists of corner-sharing octahedra (AlO₄F₂ for <b>1</b> and <b>3</b> and AlO₆ for <b>2</b>) linked together through the\nbridging CPO₃ tetrahedra of the diphosphonate groups. These chains are unusual in that each diphosphonate\nmoiety acts as a bisbidentate ligand that is coordinated to the same two metal centers through both of the O₃PC−\ngroups of the diphosphonate ligand. The arrangement of the Tancoite-like chains and charge compensation cations\nin the structures of compounds <b>1</b><b>−</b><b>3</b> is seen to be dependent upon the nature of the diphosphonic acid and\norganoammonium/ammonium cations. Careful selection of these two components may provide a method to design\nfuture materials in this system.