Harnessing Coordination Chemistry for Selective and Efficient Water Decontamination in Metal-Based Homogeneous...

Homogeneous advanced oxidation processes (AOPs) are constrained by pH-dependent metal speciation, sluggish metal redox cycling, matrix scavenging of radicals, and nonproductive decay of high-valent metal-oxo intermediates. Ligand coordination offers a coordination-chemistry strategy for overcoming these limitations by reshaping metal electronic structures, regulating oxidant activation, and redirecting reactive-species evolution. This review organizes recent advances in coordination-regulated homogeneous AOPs around O-donor, N-donor, and mixed N,O-donor ligands, and categorizes their catalytic roles into four mechanistic functions: (1) stabilizing metal centers and accelerating redox cycling; (2) steering oxidant activation toward radical or high-valent metal-oxo pathways; (3) shifting the consumption of transient high-valent intermediates from nonproductive self-decay/disproportionation toward contaminant oxidation; and (4) enabling direct nonradical electron- or O-transfer oxidation through metal-oxidant complexes. We further highlight that many proposed mechanisms still rely heavily on indirect probes, whereas emerging isotope-labeling and operando spectroscopic evidence calls for critical re-evaluation of several conventional interpretations. Future studies should emphasize multi-method mechanistic validation, environmentally benign ligand design, transformation and ecotoxicity assessment, and pilot-scale testing in real-water matrices to determine when coordination-regulated selectivity can justify added chemical demand and post-treatment requirements.