Site-selective valence isomerism as a unified electronic trigger for magnetism, chirality, and catalysis in Ni–carboxylate MOFs

Valence modulation at metal nodes provides a fundamental route to couple electronic structure with functional properties in metal–organic frameworks (MOFs). Achieving precise and stimulus-independent control of metal oxidation states within an isostructural lattice remains a central challenge. Here we demonstrate valence isomerism in a Ni–carboxylate framework, Ni3(OH)2(Cam)2(H2O)4, by combining pH adjustment with vortex-driven stirring. This approach yields an isostructural pair consisting of a Ni(II) parent phase and a mixed-valence Ni(II)/Ni(III) analog, in which approximately 25% of the Ni centers are oxidized to low-spin Ni3+ selectively at the Ni(1) sites. Subtle valence reconfiguration reorganizes the intrachain interactions within the [Ni3(OH)2] chains, reinforcing ferrimagnetic order and enhancing net magnetization. Concomitantly, the short-wavelength circular dichroism signals invert, and the oxygen-evolution overpotential decreases by ~100 mV. These results establish valence isomerism as an electronic trigger that coherently couples magnetic, chiroptical and catalytic properties in MOFs, offering a general design principle for multifunctionality in reticular materials. Site-selective valence isomerism in a Ni–carboxylate metal–organic framework simultaneously modulates magnetic properties, chiroptical response, and oxygen evolution catalysis, demonstrating that controlled metal-node valence states enable multifunctionality in reticular materials.