Hydride-Containing Eight-Electron Pt/Ag Superatoms: Structure, Bonding, and Multi-NMR Studies

Abstract

Recent reports on hydride-doped noble metal nanoclusters strongly suggest that the encapsulated hydride is a part of the <i>superatom</i> core, but no accurate location of the hydride could be experimentally proved, so far. We report herein a hydride-doped eight-electron platinum/silver alloy nanocluster in which the position of four-coordinated hydride was determined by neutron diffraction for the first time. X-ray structures of [PtHAg₁₉(dtp/desp)₁₂] (dtp = S₂P(O^<i>n</i>Pr)₂, <b>1</b>; dsep = Se₂P(O^<i>i</i>Pr)₂, <b>2</b>) describe a central platinum hydride (PtH) unit encapsulated within a distorted Ag₁₂ icosahedron, the resulting (PtH)@Ag₁₂ core being stabilized by an outer sphere made up of 7 capping silver atoms and 12 dichalcogenolates. Solid-state structures of <b>1</b> and <b>2</b> differ somewhat in the spatial configuration of their outer spheres, resulting in overall different symmetries, <i>C</i>₁ and <i>C</i>₃, respectively. Whereas the multi-NMR spectra of <b>2</b> in solution at 173 K reveal that the structure of <i>C</i>₃ symmetry is the predominant one, ¹H and ¹⁹⁵Pt NMR spectra of <b>1</b> at the same temperature disclose the presence of isomers of both <i>C</i>₁ and <i>C</i>₃ symmetry. DFT calculations found both isomers to be very close in energy, supporting the fact that they co-exist in solution. They also show that the [PtH@Ag₁₂]⁵⁺ kernel can be viewed as a closed-shell <i>superatomic</i> core, the μ₄-hydride electron contributing to its eight-electron count. On the other hand, the 1s(H) orbital contributes only moderately to the <i>superatomic</i> orbitals, being mainly involved in the building of a Pt-H bonding electron pair with the 5<i>d_z</i>²(Pt) orbital.