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

Abstract

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.

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

“…39−41 For these reasons, we have decided to focus on the development of NH 2 -MIL-101(Ti III ) (Figure 1H), a derivative of MIL-101(Ti III ) with amine functionalities on its linkers. 42 The MOF described in this work contains a small amount of aluminum, from the titanium(III) precursor used for the synthesis, and is thus a bimetallic MOF. Interestingly, only one previous literature report concerns the synthesis of Ti-based bimetallic MOFs with the MTN (MIL-100 (Figure 1E) or PCN-333 (another name for MIL-100-TATB, Figure 1G)) topology, containing scandium as a second metal.…”

“…To the best of our knowledge, until now, there have been no reports on Ti III -MOFs that contain functionalities within their linkers. Adding such functionalities could not only have an important impact on the properties of the resulting MOFs for various applications in fields such as gas adsorption or catalysis , but also open the door for further postfunctionalization of the materials to modify their properties. − For these reasons, we have decided to focus on the development of NH 2 -MIL-101­(Ti III ) (Figure H), a derivative of MIL-101­(Ti III ) with amine functionalities on its linkers …”

“… 39 − 41 For these reasons, we have decided to focus on the development of NH 2 -MIL-101(Ti III ) ( Figure 1 H), a derivative of MIL-101(Ti III ) with amine functionalities on its linkers. 42 …”