F−/OH− substitution in [H4tren]4+ and [H3tren]3+ hydroxyfluorotitanates(IV) and classification of tren cation configurations

Abstract

Three [H3tren]3+ or [H4tren]4+ hydroxyfluorotitanates(IV) are solvothermally synthesized from TiO2, tren amine, 40% HF aqueous solution and ethanol under microwave heating at 120°C and 190°C. [H4tren]·(TiF4.6(OH)1.4)2·2.7H2O (I) and β-[H3tren]·(TiF4.5(OH)1.5)·(F) (II) are described for the first time. The third compound, α-[H3tren]·(TiF4.7(OH)1.3)·(F) (III), was previously reported as a pure fluorotitanate. The structure determinations are performed from single crystal (I) and powder (II) X-ray diffraction data. The F−/OH− substitution, expected from the presence of water in the reaction medium, is characterized by chemical analyses and 19F MAS solid state NMR experiments: all three structures are built up from Ti(F,OH)62− octahedra and “free” fluoride ions or water molecules. “Free” fluoride ions are not affected by F−/OH− substitution. The electroneutrality is ensured by triprotonated or tetraprotonated tren amines which adopt specific configurations. Additionally, based on the analysis of [H3tren]3+ or [H4tren]4+ hydroxo/oxo/fluorometalates, a classification of the configurations of tren cations is proposed.