Hydrothermal Synthesis and Characterization of an Ethylenediamine-Templated Mixed-Valence Titanium Phosphate

The mixed-valence compound TiIIITiIV(HPO4)4·C2N2H9·H2O (1) is synthesized hydrothermally from titanium powder, phosphoric and boric acids, and ethylenediamine. The compound is structurally stable up to 650 °C. It loses the template and the water molecule above 250 °C, all titanium becomes TiIV at 600 °C, and the result is the new compound TiIVTiIV(HPO4)4 (2). The structures of the two compounds were determined ab initio from powder diffraction data. Crystal data: TiIIITiIV(HPO4)4·C2N2H9·H2O, I41, a = 6.371(2), c = 16.571(1) Å, V = 672.5(1) Å3, Z = 2; TiIVTiIV(HPO4)4, I41/a, a = 6.335(2), c = 16.389(1) Å, V = 657.7(1) Å3, Z = 2. Both structures are of the open type, and the frameworks are nearly identical. Compound 2, τ-Ti(HPO4)2, is the first three-dimensional titanium hydrogen phosphate. Results of magnetization, TGA, BET, X-ray thermodiffractometry, and density measurements are also presented.