A Pseudo-Icosahedral RhH2Au10 Superatom: Two Hydrogen Atoms Acting as Gold-Atom Equivalents and Modifiers

A hydrogen atom is known to act as a gold-atom-equivalent dopant in gold nanoclusters (AuNCs) by contributing to the valence electron count. To gain insights into the interaction of multiple H atoms with AuNCs, we herein synthesized a di-H-atom-doped NC, [RhH2Au10(dppp)5]3+ (RhH2Au10; dppp = 1,3-bis(diphenylphosphino)propane), by exposing [RhAu10(dppp)5]3+ (RhAu10) to H2 gas; RhAu10 was generated in situ via hydride (H–) abstraction from [RhHAu10(dppp)5]2+. Comprehensive characterization of RhH2Au10 by X-ray crystallography, NMR spectroscopy, and theoretical calculations revealed that the two H atoms occupy the two “missing” Au sites in the arachno-type RhAu10 core via dissociative adsorption of H2, forming a pseudo-icosahedral RhH2Au10 core. This core structure contrasts sharply with the previously reported di-H-atom-doped silver- or copper-based superatoms, in which the H atoms form an MH2 (M = Os, Ru, Rh) unit completely encapsulated within an icosahedral Ag12 or Cu12 shell. The RhH2Au10 core possesses an 8-electron closed-shell electronic configuration of (1S)2(1P)6, which is isoelectronic to the icosahedral RhAu12 superatom, thereby demonstrating the Au-atom equivalence of H atoms. Nevertheless, the two H atoms in the RhH2Au10 superatomic core act as structural modifiers compared to the RhAu12 superatom: (1) the degeneracy of the 1P orbitals is lifted by lowering the geometric symmetry, and (2) the HOMO–LUMO energy gap is expanded due to the reduced electronic confinement volume. This study demonstrates that multiple H atoms in a gold-based superatomic core not only behave as Au-atom equivalents but also serve as key components for modulating their fundamental properties.