O,N,O-tridentate chelation directs Mn(II)/periodate activation toward Mn(V)=O formation and selective micropollutant...

Ligand coordination has emerged as an effective strategy for steering Mn(II)-mediated periodate (PI) activation toward the formation of high-valent manganese-oxo species for micropollutant degradation, yet the influence of N/O donor-site arrangement on catalytic reactivity remains poorly understood. Herein, the relationship between N/O donor-site arrangement and Mn(II)/PI reactivity toward organic pollutants was elucidated using structurally distinct ligands. Among the tested ligands, 2,6-pyridinedicarboxylic acid with an ortho-flanked pincer-like O,N,O-tridentate coordination motif exhibited the highest catalytic performance, outperforming ligands with alternative N/O donor-site configurations by 1.2-11.3-fold. This reactivity trend indicated a close association between N/O donor-site arrangement and catalytic performance within the examined ligand series. Mn(V)=O was suggested as a plausible high-valent Mn-oxo species involved in the nonradical oxidation pathway. Density functional theory calculations provided electronic-structure and thermodynamic support for the role of O,N,O chelation in modulating the electronic structure of the Mn center, promoting I-O bond polarization in the precursor complex, and favoring the proposed formation of Mn(V)=O. An ortho-chelation score was further proposed as an empirical descriptor of position-dependent reactivity within the examined ligand series. These results highlight the favorable association of the ortho-flanked O,N,O coordination motif with Mn(II)/PI activation and provide insight into ligand-assisted selective oxidation systems for water treatment.