Atomically Precise [Cu23H4(SC7H7)18(PPh3)6] Nanocluster: Structural Integration of Johnson Solids through a Cu(0) Center and Electrocatalytic Functionality

In recent years, copper (Cu) nanoclusters (NCs) have attracted significant attention for their potential in catalytic applications. However, the inherent high reactivity of Cu(0) often leads to instability, making it challenging to synthesize stable Cu(0)-based NCs. As a result, most reported systems are limited to Cu(I)-based NCs, which in turn constrains their effectiveness and broader applicability in catalysis. Here, we present a synthetic strategy to fabricate a stable Cu(0)-containing, [Cu₂₃H₄(SC₇H₇)₁₈(PPh₃)₆] NC, where the Cu(0) center is atomically protected by two Cu(I)-based Johnson solids and stabilized by the additional Cu(I) units, thiolate ligands and interstitial hydrides. Although neutral PPh₃ ligands are also present, their attachment is positioned away from the Cu(0) center, primarily serving to stabilize the overall geometry and prevent further structural distortions. This robust architectural framework enables the NC to maintain exceptional structural stability and catalytic performance in electrochemical CO₂ reduction reactions, facilitating a consistent selectivity for the end product over time. Density functional theory calculations validate the experimental findings, confirming HCOOH as the preferred product. This preference arises from the lower limiting potential for *HCOO formation, attributed to its enhanced stabilization through a favorable combination of electronic and geometric structure─features that clearly distinguish it from Cu(I) NCs.