An Ultra-Stable Cr-Hydroxamate Metal-Organic Framework From Postsynthetic Transmetalation

Hydroxamate-based metal-organic frameworks (MOFs) have attracted increasing interest due to their strong chelating ability and inherent chemical robustness; however, their stability has yet to rival that of conventional carboxylate-based MOFs. Herein, using a tris-hydroxamic acid linker (H₃TATPHA), we report a family of isostructural MOFs (SUM-86) incorporating Ga(III), In(III), and Fe(III) with a two-fold interpenetrated srs topology. Remarkably, nearly quantitative transmetalation of SUM-86(In) with Cr(III) affords SUM-86(Cr) in a single-crystal-to-single-crystal manner, preserving framework topology and morphology. Benefiting from the inert coordination chemistry of Cr(III) and strong hydroxamate chelation, SUM-86(Cr) exhibits exceptional chemical stability, retaining crystallinity in boiling water and in highly corrosive aqueous solutions, including 3 M HCl and 5 M NaOH. Moreover, SUM-86(Cr) shows rapid and high-capacity iodine adsorption from solution. This work establishes an effective strategy for accessing ultra-stable hydroxamate-based MOFs and highlights postsynthetic transmetalation as a powerful approach for framework fine-tuning and stability enhancement.