Engineering Single-Atom Sites with the Irving-Williams Series for the Simultaneous Co-photocatalytic CO₂ Reduction...

The bonding effects between 3d transition-metal single sites and supports originate from crystal field stabilization energy (CFSE). The 3d transition-metal atoms of the spontaneous geometrical distortions, that is the Jahn-Teller effect, can alter CFSE, thereby leading to the Irving-Williams series. However, engineering single-atom sites (SASs) using the Irving-Williams series as an ideal guideline has not been reported to date. Herein, alkynyl-linked covalent phenanthroline frameworks (CPFs) with phenanthroline units are developed to anchor the desired 3d single metal ions from d₅ to d₁₀ (Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺). The Irving-Williams series was employed to accurately predict the bonding effects between 3d transition-metal atoms and phenanthroline units. To verify this, theoretical calculations and experimental results reveal that Cu-SASs/CPFs exhibits higher stability and faster charge-transfer efficiency, far surpassing other metal-SASs/CPFs. As expected, Cu-SASs/CPFs demonstrates a high photoreduction of CO₂-to-CO activity (~30.3 μmol ⋅ g^-1 ⋅ h^-1) and an exceptional photooxidation of CH₃CHO-to-CH₃COOH activity (~24.7 μmol ⋅ g^-1 ⋅ h^-1). Interestingly, the generated *O₂ ^- is derived from the process of CO₂ reduction, thereby triggering a CH₃CHO oxidation reaction. This work provides a novel design concept for designing SASs by the Irving-Williams to regulate the catalytic performances.