[PtAu24(SC2H4Ph)(18)](0) ( [PtAu24](0)) was fully and selectively converted to [PtAu24](-), having an open electronic structure with seven valence electrons, upon the addition of an equiamount of NaBH4. Stoichiometric production of [PtAu24](-) by the reaction between an equal amount of [PtAu24](0) and [PtAu24](2-) revealed that the above reaction proceeds via the spontaneous electron transfer (ET) from [PtAu24](2-) nascently reduced by H--mediated reduction to [PtAu24](0) remaining in the solution. Theoretical calculation suggested that the driving force of this novel ET reaction was the larger adiabatic electron affinity of [PtAu24](0) compared to that of [PtAu24](-), partly associated with reduction-induced relief of the Jahn-Teller strain. We propose that ET proceeds via the dimer complex of [PtAu24](2-) and [PtAu24](0) formed through the aurophilic interaction between Au(I) sites in the surface layer.