Correlating Precise Coordination Environments to Charge-Transfer Kinetics in Heterometallic Coordination Polymers: A Crystallography-Driven Photocatalytic Study

Abstract We propose a crystal-guided heterometal engineering strategy in coordination polymers (CPs) that directly correlates precise structural modulation induced by secondary metal ions with their charge carrier kinetics during the photocatalytic degradation of rhodamine B (RhB). This result is achieved by indispensable growth of single crystals of CoZn-CP and NiZn-CP through exquisite control of both metal-ion stoichiometry and crystallization parameters. Single-crystal X-ray diffraction (XRD) revealed their isoreticular topologies to parent Zn-CP while exhibiting cation-specific coordination alterations, namely, coordination geometries, lattice distortions, and metal distributions. X-ray photoelectron spectroscopy (XPS) and ICP further quantified actual substitution ratios and unveiled distinct metal-ion distributions. CoZn-CP achieves 100% degradation of RhB under UV irradiation for 60 min, substantially outperforming both parent Zn-CP (79.3%) and NiZn-CP (88.9%). By linking the coordination structure and charge-transfer kinetics, we attribute its exceptional performance to the intrinsically compatible radius and favorable electronic configuration of Co2+, which facilitate higher-concentration doping into the host framework (32%), retain unsaturated metal sites, forge a stronger ligand-to-metal charge transfer pathway, and narrow the band gap. These benign structural and electronic refinements boost photocurrent generation, lower transfer resistance, and suppress photoluminescence with an extended average lifetime, synergistically yielding superior photocatalytic efficacy. Reactive species, photostability, photocatalytic mechanism, and degradation pathways of RhB in CoZn-CP were investigated thoroughly.