Reticular Synthesis of a Highly Stable Homochiral Cr3+-Based Metal–Organic Framework for Enantioselective Separation

Abstract

Homochiral porous metal–organic frameworks (HMOFs) are highly promising as enantioselective adsorbents. However, reports on HMOFs, especially those with high stability, are still scarce, restricting their applications in enantioseparation, particularly in the resolution of highly reactive amines with important pharmaceutical value, which can potentially dissociate MOF structures. Synthesizing new and stable chiral MOFs remains an urgent and important task for the current MOF development. In this study, a new robust chiral Cr-MOF, Cr-SXU-5, has been constructed using S-1,1-bi-2-naphthol (BINOL) as the chirality source by converting corresponding Fe-MOFs, Fe-SXU-5, through a solvent-assisted metal metathesis under mild conditions. In contrast to the vulnerable Fe-SXU-5, Cr-SXU-5 exhibited high stability under various conditions, including exposure to 3 M HCl and pH = 12 NaOH aqueous solutions. The results demonstrated that Cr-SXU-5 not only exhibits good adsorption selectivity for CO₂/N₂ (15/85) and C₂H₂/CO₂ (50/50) but also can effectively separate several chiral amines, particularly 3-methylbutan-2-amine, achieving an enantiomeric excess (ee) value of over 99.3%, which is the highest among reported HMOFs. Furthermore, Cr-SXU-5 also showed excellent recyclability, maintaining its separation efficiency and structural integrity over multiple cycles.