Hierarchical Heterometallic Coordination Underpins Alkali Tolerance in a Zr–Cu Hydroxamate Framework

Abstract

Chemical robustness in heterometallic metal–organic frameworks depends on the strength and organization of chemically distinct coordination bonds. We report SUM-71, a three-dimensional Zr–Cu hydroxamate framework integrating Zr–O/Cu–O rods with Cu–N cross-links. Its characteristic powder X-ray diffraction peaks persist after 24 h in common solvents, aqueous media spanning pH 2–14, and near-saturated NaOH (ca. 20 M); measurable microporosity also persists after acid and alkaline treatment. Cluster density functional theory calculations find endothermic water substitution at all modeled sites and greater thermodynamic resistance at rod-forming interactions than at Cu–N cross-links. In 0.1 M KOH, SUM-71/nickel foam retains a nearly unchanged composite-electrode polarization response after 500 cycles, with SUM-71 diffraction peaks remaining detectable. These results highlight differentiated coordination roles as a strategy for exceptional static alkali tolerance.