Metal–organic frameworks (MOFs) incorporating redox-sensitive metal centers, such as Ti(III) and Mn(III), offer unique opportunities for designing materials with tunable properties and dynamic behavior. However, their relative instability under ambient conditions has limited their exploration. In this talk, I will present our investigations on Ti(III)- and Mn(III)-based MOFs, focusing on their synthesis, structural transformations, and guest sorption properties. To develop mesoporous Ti(III)-MOFs, we explored the use of the inexpensive precursor (TiCl3 )3 ·AlCl3 under inert conditions. A crystalline MOF from the NH2 -MIL-101 family – structurally related to its Cr, Al, and Fe analogues – was successfully obtained after screening various synthesis conditions. This material shows notable gas sorption performance and retains structural stability up to 200 °C, making it a promising candidate for hydrogen storage and other gas-related applications. In contrast, the Mn(III)-MOFs are synthesized without the need for inert conditions, via self-oxidation of Mn(II) in the presence of aromatic dicarboxylate linkers. This strategy yielded a series of new frameworks, including non-flexible members of the MIL-47/MIL-53 and MIL-69 families, as well as distinctive wine-rack-like structures (UcL-1 and UcL-2). These exhibit reversible crystalline-to-amorphous transitions upon guest release. To gain deeper insights into these materials, we employ X-ray pair distribution function (PDF) analysis. This technique provides crucial insight into local structural changes, particularly in amorphous MOFs, and helps clarify the effects of oxidation and guest removal. Together, these studies enhance our understanding of MOFs constructed from redox-sensitive metal centers and highlight new design strategies for materials with dynamic structural behavior and gas sorption capabilities.
Steenhaut et al. (Wed,) studied this question.