Hydrothermal Synthesis and Structural Characterization of Three Organically Templated Titanium Phosphates:  Ti₂(HPO₄)₂(PO₄)₂·C₂N₂H₁₀, Ti₃(H₂PO₄)(HPO₄)_3.5(PO₄)₂·C₂N₂H₁₀, and Ti₇(HPO₄)₆(PO₄)₆·C₃N₂H₁₂

Abstract

Three organically templated titanium phosphates with the formulas Ti2(HPO4)2(PO4)2·C2N2H10 (1), Ti3(H2PO4)(HPO4)3.5(PO4)2·C2N2H10 (2), and Ti7(HPO4)6(PO4)6·C3N2H12 (3) have been prepared hydrothermally from titanium powder, phosphoric acid, and structure-directing organic amines. The as-synthesized products are characterized by powder X-ray diffraction, 31P MAS NMR spectroscopy, IR spectroscopy, and thermogravimetric and differential thermal analyses (TG-DTA). The structures have been solved by single-crystal X-ray diffraction analysis. Crystal data for 1: triclinic, P1̄, a = 6.3066(17) Å, b = 10.181(4) Å, c = 12.644(3) Å, α = 102.14(2)°, β = 102.49(3)°, γ = 90.00(2)°, Z = 2. Crystal data for 2: triclinic, P1̄, a = 10.3183(9) Å, b = 10.7501(10) Å, c = 10.8315(10) Å, α = 73.436(2)°, β = 79.648(2)°, γ = 83.260(2)°, Z = 2. Crystal data for 3: trigonal, R3̄, a = 16.4993(15) Å, b = 16.4993(15) Å, c = 12.704(3) Å, Z = 3. Their frameworks are all built up with TiO6 octahedra and PO4, PO2(OH)2, PO3(OH), and/or PO2(O)(OH) tetrahedral units. Compound 1 is an ethylenediamine intercalated layered titanium phosphate in which the layers are similar to that of γ-type titanium phosphate. Both 2 and 3 are of open-framework type, and the diprontonated organic amine molecules are entrapped in 12-membered-ring channels for 2 and 8-membered-ring channels for 3.