Poly-Hydride [Au I 7 (PPh 3 ) 7 H 5 ](SbF 6 ) 2 cluster complex: Structure, Transformation, and Electrocatalytic CO 2 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 [Au 7 (PPh 3 ) 7 H 5 ](SbF 6 ) 2 (abbrev. Au 7 H 5 2+ ), an Au cluster complex containing five hydride ligands, which decomposed to give [Au 8 (PPh 3 ) 7 ] 2+ (abbrev. Au 8 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 CO 2 reduction reaction (CO 2 RR): Au 7 H 5 2+ exhibited 98.2 % selectivity for H 2 , whereas Au 8 2+ was selective for CO (73.5 %). Further DFT calculations showed that the H - ligand inhibited the CO 2 RR process compared with the electron-donor H.