Phosphinous Acid-Phosphinito Tetra-Icosahedral Au 52 Nanoclusters for Electrocatalytic Oxygen Reduction.

While the formation of superatomic nanoclusters by the three-dimensional assembly of icosahedral units was predicted in 1987, the synthesis and structural determination of such clusters have proven to be incredibly challenging. Herein, we employ a mixed-ligand strategy to prepare phosphinous acid-phosphinito gold nanocluster Au 52 (HOPPh 2 ) 8 (OPPh 2 ) 4 (TBBT) 16 with a tetra-icosahedral kernel. Unlike expected, each icosahedral Au 13 unit shares one vertex gold atom with two adjacent units, resulting in a "puckered" ring shape with a nuclearity of 48 in the kernel. The phosphinous acid-phosphinito ligand set, which consists of two phosphinous acids and one phosphinito motif, has strong intramolecular hydrogen bonds; the π-π stacking interactions between the phosphorus- and sulfur-based ligands provide additional stabilization to the kernel. Highly stable Au 52 (HOPPh 2 ) 8 (OPPh 2 ) 4 (TBBT) 16 serves as an effective electrocatalyst in the oxygen reduction reaction. Density functional theory calculations suggest that the phosphinous acid-phosphinito ligands provide the most active sites in the electrochemical catalysis, with O* formation being the rate-determining step.