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.