Understanding Doping Effects on Electronic Structures of Gold Superatoms: A Case Study of Diphosphine-Protected...

Dopants into ligand-protected Au superatoms have been hitherto limited to group X-XII elements (Pt, Pd, Ag, Cu, Hg, and Cd). To expand the scope of the dopants to the group IX elements, we synthesized unprecedented [IrAu₁₂(dppe)₅Cl₂]⁺ [IrAu; dppe = 1,2-bis(diphenylphosphino)ethane] and [PtAu₁₂(dppe)₅Cl₂]²⁺ (PtAu) and compared their electronic structures with that of [Au₁₃(dppe)₅Cl₂]³⁺ (Au). Single-crystal X-ray diffractometry, ³¹P{¹H} NMR, and Ir L₃-edge extended X-ray absorption fine structure analysis of IrAu revealed that the single Ir atom is located at the center of the icosahedral IrAu₁₂ core. Electrochemical analysis demonstrated that the energy levels of the highest occupied molecular orbitals are upshifted in the order of Au < PtAu < IrAu. This trend was qualitatively explained in such a manner that the jellium core potential at the central position becomes shallower by replacing Au⁺ with Pt⁰ and further with Ir^-. IrAu underwent reversible redox reactions between the charge states of 1+ and 2+. The gradual increase of the energy gap between the highest occupied molecular orbital and lowest unoccupied molecular orbital in the order of Au < PtAu < IrAu was observed by electrochemical measurement and optical spectroscopy. This study provides a simple guiding principle to tune the electronic structures of heterometal-doped superatoms.