Synthesis, structure and solid state NMR analysis of a new templated titanium(III/IV) fluorophosphate

Abstract

Abstract The title compound MIL-131 (MIL stands for Material from Institut Lavoisier) was prepared hydrothermally (4 days, 473 K, autogenous pressure) in the presence of an organic base (N((CH2)2NH2)3). The structure of MIL-131 or TiIIITiIV(OH)F4(HPO4)·(PO4)·(N((CH2)2NH3)3) has been determined ab initio from X-Ray synchrotron powder diffraction data using simulated annealing methods and was refined in the triclinic space group P-1 (no. 2). MIL-131 exhibits a one-dimensional structure built up from inorganic chains of corner sharing TiO5(OH) titanium(III) octahedra and PO4 and HPO4 phosphate tetrahedra, related to TiO2F4 titanium octahedra. Protonated triamine cations are located between the inorganic motifs, and interact strongly with the mineral network through hydrogen bondings both with terminal fluorine atoms and hydroxo or oxo groups. Multinuclear solid state NMR has allowed a clear attribution of the protons, fluoride, and phosphate groups environment within the framework of MIL-131. The large values of chemical shift anisotropy together with the absence of any 13C NMR response confirmed the presence of paramagnetic titanium(III) species deduced from the crystal structure. Finally, 2D MAS 1H-31P CP-HETCOR NMR correlation experiment gives some insight on the nature of the intra-framework hydrogen bonding. Crystal data for MIL-131: a = 14.109(1) A, b = 8.462(3) A, c = 7.179(1) A, α = 93.772(1)°, β = 96.566(2)°, γ = 98.004(1)°, V = 840.36(2) A3, z = 2.