A Double Open-Shelled Au₄₃ Nanocluster with Increased Catalytic Activity and Stability

Atomically precise metal nanoclusters (NCs) are an intriguing class of crystalline solids with unique physicochemical properties derived from tunable structures and compositions. Most atomically precise NCs require closed-shells and coordinatively saturated surface metals in order to be stable. Herein, we report Au₄₃(C≡C^tBu)₂₀ and Au₄₂Ag₁(C≡C^tBu)₂₀, which feature open electronic and geometric shells, leading to both paramagnetism (23 valence e^-) and enhanced catalytic activity from a single coordinatively unsaturated surface metal. The Au-alkynyl surface motifs of these NCs form five helical stripes around the inner Au₁₂ kernel, imparting chirality and high thermal stability. Density functional theory (DFT) calculations suggest that there are minimal energy differences between the open-shelled NCs and hypothetical closed-shell systems and that the open-shelled electronic configuration gives rise to the largest band gap, which is known to promote cluster stability. Furthermore, we highlight how coordinatively unsaturated surface metals create active sites for the catalytic oxidation of benzyl alcohol to benzaldehyde, leading to high selectivity and increased conversion. This work represents the first example of an atomically precise Au NC with a double open-shelled structure and provides a promising platform for investigating the magnetic and catalytic properties of noble metal nanoparticles.