Synthesis, Structure, and Thermal Stability of a Mesoporous Titanium(III) Amine-Containing MOF

The first mesoporous bimetallic Ti^III/Al metal-organic framework (MOF) containing amine functionalities on its linkers has been selectively obtained by converting the cheap commercially available (TiCl₃)₃AlCl₃ into Ti_3-AlCl₃(THF)₃ and reacting this complex with 2-aminoterephthalic acid in dimethylformamide (DMF) under soft solvothermal conditions. This compound is structurally related to the previously described NH₂-MIL-101(M) (M = Cr, Al, and Fe) MOFs. Thermal gravimetric analyses and in situ powder X-ray diffraction (PXRD) measurements demonstrated that this highly air-sensitive Ti^III-containing MOF is structurally stable up to 200 °C. Nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, and inductively coupled plasma (ICP) revealed that NH₂-MIL-101(Ti^III) contains trinuclear Ti₃(μ₃-O)Cl(DMF)₂(RCOO)₆ clusters with strongly bound DMF molecules and a small amount of aluminum. Sorption experiments revealed a higher affinity of this MOF for hydrogen compared to the previously described monometallic unfunctionalized MIL-101(Ti^III) MOF.