The synthesis and characterization of a new diphosphine-protected gold hydride nanocluster

Gold is the most inert metal and does not form a bulk hydride. However, gold becomes chemically active in the nanometer scale and gold nanoparticles have been found to exhibit important catalytic properties. Here, we report the synthesis and characterization of a highly stable ligand-protected gold hydride nanocluster, [Au₂₂H₃(dppee)₇]³⁺ [dppee = bis(2-diphenylphosphino) ethyl ether]. A synthetic method is developed to obtain high purity samples of the gold trihydride nanocluster with good yields. The properties of the new hydride cluster are characterized with different experimental techniques, as well as theoretical calculations. Solid samples of [Au₂₂H₃(dppee)₇]³⁺ are found to be stable under ambient conditions. Both experimental evidence and theoretical evidence suggest that the Au₂₂H₃ core of the [Au₂₂H₃(dppee)₇]³⁺ hydride nanocluster consists of two Au₁₁ units bonded via two triangular faces, creating six uncoordinated Au sites at the interface. The three H atoms bridge the six uncoordinated Au atoms at the interface. The Au₁₁ unit behaves as an eight-electron trivalent superatom, forming a superatom triple bond (Au₁₁ ≡ Au₁₁) in the [Au₂₂H₃(dppee)₇]³⁺ trihydride nanocluster assisted by the three bridging H atoms.