M16Ni24(CO)40]4–: Coinage Metal Tetrahedral Superatoms as Useful Building Blocks Related to Pyramidal Au20 Clusters (M = Cu, Ag, Au). Electronic and Bonding Properties from Relativistic DFT Calculations

Abstract

Characterization of the tetrahedral Au20 structure in the gas phase remains a major landmark in gold cluster chemistry, where further efforts to stabilize this bare 20-electron superatom in solution to extend and understand its chemistry have failed so far. Here, we account for the structural, electronic, and bonding properties of [M16Ni24(CO)40]4– (M = Cu, Ag, Au) observed in solution for gold and silver. Our results show a direct electronic relationship with Au20, owing that such species share a common tetrahedral [M16]4– central core with a 1S21P61D102S2 jellium configuration. In the case of Au20, the [Au16]4– core is capped by four Au+ ions, whereas in [M16Ni24(CO)40]4– it is capped by four Ni6(CO)10 units. In both cases, the capping entities are a full part of the superatom entity, where it appears that the free (uncapped) [M16]4– species must be capped for further stabilization. It follows that the Ni6(CO)10 units in [M16Ni24(CO)40]4– should not be considered as external ligands as their bonding wit...