Proximity Engineering of Fe‒N ₄ Twins for Oriented Generation of Singlet Oxygen for Hospital Wastewater Treatment

ABSTRACT Precisely tailoring the molecular configurations of single‐atom sites and elucidating their correlation with generated specific reactive species is crucial for advancing Fenton‐like chemistry toward targeted remediation. Herein, we developed a facile approach to precisely modulate the distances between isolated Fe‒N 4 sites (d Fe–Fe ) from nanometer (0.95 nm) to subnanometer (0.43 nm) to construct a family of well‐defined Fe‒N 4 twins with manipulated ligand‐field strength and spin states. Different Fe‒N 4 twin sites trigger a metal‐loading‐independent volcano‐shaped Fenton‐like activity trend. The optimal configuration, achieved at an Fe‒Fe distance of 0.43 nm (Fe d0.43 SA), induces an intermediate‐spin (t 2g 4e g 1) configuration that optimizes e g orbital occupancy, thereby promoting peroxymonosulfate (PMS) adsorption to form *HSO 5 − and subsequently lowers the energy barrier for coupling with another PMS to selectively generate singlet oxygen ( 1 O 2 ). The robust molecular catalyst with Fe‒N 4 twin sites sustains over 120 h of continuous treatment of organic wastewater and demonstrates simultaneous disinfection and pharmaceutical removal of actual hospital wastewater. This work presents an advanced strategy for engineering single‐atom sites with multi‐site cooperativity to regulate Fenton‐like catalysis, enabling rapid and real‐world water purification.