Synthesis, structure and thermal stability of a mesoporous titanium(III) amine containing MOF with improved hydrogen sorption properties

The first mesoporous bimetallic TiIII/Al metal-organic framework (MOF) containing amine functionalities on its linkers has been selectively obtained by converting the cheap commercially available (TiCl3)3AlCl3 into Ti3-xAlxCl3(THF)3 and reacting this complex with 2-aminoterephthalic acid in 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 PXRD measurements demonstrated that this highly air-sensitive TiIII-containing MOF is structurally stable up to 200°C. Nuclear magnetic resonance (NMR) spectroscopy, elemental and inductively-coupled plasma (ICP) analyses revealed that NH2-MIL-101(TiIII) contains trinuclear Ti3(μ3-O)Cl(DMF)2(RCOO)6 clusters with strongly bound DMF molecules, and a small amount of aluminum. Sorption experiments reveal a higher affinity of this MOF for hydrogen compared to the previously described monometallic unfunctionalized MIL-101(TiIII) MOF.