Toward the Solution Synthesis of the Tetrahedral Au₂₀ Cluster

Abstract

We report the observation in solution of the recently discovered tetrahedral Au20 cluster coordinated with eight PPh3 (Ph = phenyl) ligands. The composition and molecular weight of the Au20(PPh3)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 PPh3 ligands can be easily removed from Au20(PPh3)82+, resulting in a highly stable Au20(PPh3)42+ ion. This observation is consistent with the tetrahedral Au20, in which the four apex sites are expected to bond to the PPh3 ligands strongly, and is confirmed by theoretical calculations that predict a highly stable Au20(PH3)4 complex with Au−PH3 bond energies of ∼1 eV. The current experimental and theoretical observations suggest that large quantities of ligand-stabilized tetrahedral Au20 can be obtained, opening the door for exploring its anticipated novel chemical, optical, and catalytic properties.