Hydrothermal synthesis and ab initio structurfal approach of two new layered oxyfluorinated titanium(IV) phosphates: Ti2(PO4)2F4·N2C2H10 (MIL-6) and Ti2(PO4)2F4·N2C3H12·H2O

Abstract

Ti ₂ (PO ₄ ) ₂ F ₄ ·N ₂ C ₂ H ₁₀ (MIL-6) and Ti ₂ (PO ₄ ) ₂ F ₄ ·N ₂ C ₃ H ₁₂ ·H ₂ O were prepared hydrothermally (3 days, 453-483 K, autogenous pressure) in the presence of an organic template (ethylenediamine or 1,3-diaminopropane). The structures of Ti ₂ (PO ₄ ) ₂ F ₄ ·N ₂ C ₂ H ₁₀ 1 and Ti ₂ (PO ₄ ) ₂ F ₄ ·N ₂ C ₃ H ₁₂ ·H ₂ O 2 were determined ab initio from powder diffraction data. These structures exhibit different monoclinic distortions of the VOPO ₄ ·2H ₂ O structure type. 1: space group P2 ₁ /c (no. 14), a=7.508(1), b=8.881(1), c=8.961(1) Å, β=107.22(1)° and V=570.8(1) Å ³ . 2: space group C2 (no. 5), a=16.820(2), b=6.333(2), c=6.331(2) Å, β=106.20° and V=645.8(1) Å ³ . Both are layered compounds built up from TiO ₄ F ₂ octahedra linked together by PO ₄ tetrahedra; the Ti-F bonds are oriented perpendicularly to the layers which contain the diprotonated amine. The stability of the structures is ensured by the strong hydrogen bonding between the fluorine atoms and the amino groups.