Hydrothermal synthesis and characterization of an ethylenediamine-templated mixed-valence titanium phosphate

The mixed-valence compound (TiTiIV)-Ti-III(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 degrees C. It loses the template and the water molecule above 250 degrees C, all titanium becomes Ti-IV at 600 degrees C, and the result is the new compound (TiTiIV)-Ti-IV(HPO4)(4) (2). The structures of the two compounds were determined ab initio from powder diffraction data. Crystal data: (TiTiIV)-Ti-III(HPO4)(4). C2N2H9. H2O, I4(1), a = 6.371(2), 16.571(1) Angstrom,V = 672.5(1) Angstrom(3), Z = 2; (TiTiIV)-Ti-IV(HPO4)(4), I4(1)/a, a = 6.335(2), c = 16.389(1) Angstrom, V = 657.7(1) Angstrom(3), Z = 2. Both structures are of the open type, and the frameworks are nearly identical. Compound 2, tau-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.