Poly-Hydride [AuI 7 (PPh3 )7 H5 ](SbF6 )2 cluster complex: Structure, Transformation, and Electrocatalytic CO2 Reduction Properties

Hydride Au^I bonds are labile due to the mismatch in electric potential of an oxidizing metal and reducing ligand, and therefore the structure and structure-activity relationships of nanoclusters that contain them are seldom studied. Herein, we report the synthesis and characterization of [Au₇ (PPh₃ )₇ H₅ ](SbF₆ )₂ (abbrev. Au₇ H₅ ²⁺ ), an Au cluster complex containing five hydride ligands, which decomposed to give [Au₈ (PPh₃ )₇ ]²⁺ (abbrev. Au₈ ²⁺ ) upon exposure to light (300 to 450 nm). The valence state of Au^I and H^- was verified by density functional theory (DFT) calculations, NMR, UV/Vis and XPS. The two nanoclusters behaved differently in the electrocatalytic CO₂ reduction reaction (CO₂ RR): Au₇ H₅ ²⁺ exhibited 98.2 % selectivity for H₂ , whereas Au₈ ²⁺ was selective for CO (73.5 %). Further DFT calculations showed that the H^- ligand inhibited the CO₂ RR process compared with the electron-donor H.