π-Contraction Induces High‑Spin Co Centers in 2D Conductive MOFs for Efficient Oxygen Reduction.

Two-dimensional conductive metal-organic frameworks (c-MOFs) are promising electrocatalysts for the oxygen reduction reaction (ORR), yet nearly all optimization strategies have focused on metal-node modification while the ligand scaffold remains largely unexplored. Here, we report an unconventional "π-contraction" strategy that excises the peripheral benzene rings from metallophthalocyanine (MPc) to afford contracted metalloporphyrazine (MPz) ligands (M = Co, Ni). Trimming decreases π-electron density on the carbon framework and directs charge to the metal center, thereby reshaping its electronic structure. In CoPz-MOF, this contraction uniquely induces a high-spin Co 3d station and stabilizes mixed Co(I)/Co(II) valence states-features absent in CoPc MOF and Ni-based analogues. DFT calculations confirm that the high-spin configuration confers the strongest oxygen adsorption affinity among the series, while the presence of Co(I) species further promotes O2 chemisorption during the onset stage of ORR. Electrochemically, CoPz-MOF delivers a half-wave potential of 0.84 V with a preferential four-electron pathway, outperforming its counterparts. In zinc-air batteries, it achieves a peak power density of 125.6 mW cm-2 and stable operation over 500 h. This work establishes ligand-level conjugation engineering-rather than node-metal substitution-as a powerful strategy for tailoring metal-center electronic structures in c-MOF electrocatalysts.