Toward the Solution Synthesis of the Tetrahedral Au₂₀ Cluster

We report the observation in solution of the recently discovered tetrahedral Au 20 cluster coordinated with eight PPh 3 (Ph = phenyl) ligands. The composition and molecular weight of the Au 20 (PPh 3 ) 8 complex were confirmed by the isotopic pattern and accurate mass measurement of its doubly charged cation using high-resolution mass spectrometry. A collision-induced dissociation experiment showed that four PPh 3 ligands can be easily removed from Au 20 (PPh 3 ) 8 2+, resulting in a highly stable Au 20 (PPh 3 ) 4 2+ ion. This observation is consistent with the tetrahedral Au 20, in which the four apex sites are expected to bond to the PPh 3 ligands strongly, and is confirmed by theoretical calculations that predict a highly stable Au 20 (PH 3 ) 4 complex with Au−PH 3 bond energies of ∼1 eV. The current experimental and theoretical observations suggest that large quantities of ligand-stabilized tetrahedral Au 20 can be obtained, opening the door for exploring its anticipated novel chemical, optical, and catalytic properties.