A Lead(II)-Based Coordination Polymer Exhibiting Photocatalytic and Electrochemical CO₂ Reduction Activities

Mixed-anion compounds incorporating multiple anionic species within a single crystal lattice can exhibit novel structural and functional properties and so have recently attracted much attention. These materials offer unique coordination environments that can lead to emergent behaviors relevant to various applications. Coordination polymers (CPs) comprising metal centers bridged by molecular anionic linkers represent a subclass of mixed-anion compounds and are of interest. In particular, CPs featuring metal-sulfur (-M-S-)_n frameworks are promising candidates for optoelectronic and catalytic applications due to the unique light absorption characteristics of these materials. The present study synthesized and characterized a new visible-light-responsive Pb(II)-based CP, termed STF-1 (Science Tokyo Framework 1; [Pb(mptt)₂]_n, mptt = 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thiolate). This CP exhibits an optical bandgap of 2.50 ± 0.2 eV and so is responsive to visible light. STF-1 also demonstrates charge carrier transport through the mptt ligand moiety, as supported by first-principles density functional theory calculations. Photocatalytic experiments under visible light irradiation established that STF-1 selectively reduces CO₂ to formate with high selectivity and minimal hydrogen evolution. Additionally, STF-1 shows activity as a pre-electrocatalyst for CO₂ conversion in aqueous media.