Unveiling the Remarkable Stability and Catalytic Activity of a 6-Electron Superatomic Ag₃₀ Nanocluster for CO₂...

Nanocluster catalysts face a significant challenge in striking the right balance between stability and catalytic activity. Here, we present a thiacalix[4]arene-protected 6-electron [Ag₃₀(TC4A)₄(ⁱPrS)₈] nanocluster that demonstrates both high stability and catalytic activity. The Ag nanocluster features a metallic core, Ag₁₀⁴⁺, consisting of two Ag₃ triangles and one Ag₄ square, shielded by four {Ag₅@(TC4A)₄} staple motifs. Based on DFT calculations, the Ag₁₀⁴⁺ metallic kernel can be viewed as a trimer comprising 2-electron superatomic units, exhibiting a valence electron structure similar to that of the Be₃ molecule. Notably, this is the first crystallographic evidence of the trimerization of 2-electron superatomic units. Ag can reduce CO₂ into CO with a Faraday efficiency of 93.4% at -0.9 V versus RHE along with excellent long-term stability. Its catalytic activity is far superior to that of the chain-like Ag^I polymer _∞¹{[H₂Ag₅(TC4A)(ⁱPrS)₃]} (_∞¹Ag), with the composition similar to Ag. DFT calculations elucidated the catalytic mechanism to clarify the contrasting catalytic performances of the Ag and _∞¹Ag polymers and disclosed that the intrinsically higher activity of Ag may be due to the greater stability of the dual adsorption mode of the *COOH intermediate on the metallic core.