Atomically Precise Silver Clusters Stabilized by Lacunary Polyoxometalates with Photocatalytic CO₂ Reduction Activity

The syntheses of atomically precise silver (Ag) clusters stabilized by multidentate lacunary polyoxometalate (POM) ligands have been emerging as a promising but challenging research direction, the combination of redox-active POM ligands and silver clusters will render them unexpected geometric structures and catalytic properties. Herein, we report the successful construction of two structurally-new lacunary POM-stabilized Ag clusters, TBA₆ H₁₄ Ag₁₄ (DPPB)₄ (CH₃ CN)₉ [Ag₂₄ (Si₂ W₁₈ O₆₆ )₃ ] ⋅ 10CH₃ CN ⋅ 9H₂ O ({Ag₂₄ (Si₂ W₁₈ O₆₆ )₃ }, TBA=tetra-n-butylammonium, DPPB=1,4-Bis(diphenylphosphino)butane) and TBA₁₄ H₆ Ag₉ Na₂ (H₂ O)₉ [Ag₂₇ (Si₂ W₁₈ O₆₆ )₃ ] ⋅ 8CH₃ CN ⋅ 10H₂ O ({Ag₂₇ (Si₂ W₁₈ O₆₆ )₃ }), using a facile one-pot solvothermal approach. Under otherwise identical synthetic conditions, the molecular structures of two POM-stabilized Ag clusters could be readily tuned by the addition of different organic ligands. In both compounds, the central trefoil-propeller-shaped {Ag₂₄ }¹⁴⁺ and {Ag₂₇ }¹⁷⁺ clusters bearing 10 delocalized valence electrons are stabilized by three C-shaped {Si₂ W₁₈ O₆₆ } units. The femtosecond/nanosecond transient absorption spectroscopy revealed the rapid charge transfer between {Ag₂₄ }¹⁴⁺ core and {Si₂ W₁₈ O₆₆ } ligands. Both compounds have been pioneeringly investigated as catalysts for photocatalytic CO₂ reduction to HCOOH with a high selectivity.