Supervalence Bonding in Bi-icosahedral Cores of [M(1)Au(37)(SC(2)H(4)Ph)(24)](−) (M = Pd and Pt): Fusion-Mediated Synthesis and Anion Photoelectron Spectroscopy

[Image: see text] Au(38)(PET)(24) (PET = SC(2)H(4)Ph) is known to have a bi-icosahedral Au(23) core consisting of two Au(13) icosahedrons by sharing three Au atoms. Previous theoretical studies based on a supervalence bond (SVB) model have demonstrated that the bonding scheme in the Au(23) core is similar to that in the F(2) molecule. The SVB model predicted that the electron configuration of the Au(23) core with 14 valence electrons is expressed as (1Σ)(2)(1Σ*)(2)(1Π)(4)(2Σ)(2)(1Π*)(4) where each orbital is created by the bonding and antibonding interactions between the 1S and 1P superatomic orbitals of the icosahedral Au(13) units. Therefore, the bi-icosahedral Au(23) can be viewed as a di-superatomic molecule. To validate the SVB model, we herein conducted anion photoelectron spectroscopy (PES) on [M(1)Au(37)(PET)(24)](−) (M = Pd and Pt), which are isoelectronic and isostructural with Au(38)(PET)(24). To this end, the neutral precursors [M(1)Au(37)(PET)(24)](0) were first synthesized by fusion reactions between hydride-doped clusters [HAu(9)(PPh(3))(8)](2+) and [M(1)Au(24)(PET)(18)](−). The formation of bi-icosahedral M(1)Au(22) cores with open electronic structure in [M(1)Au(37)(PET)(24)](0) was confirmed by single-crystal X-ray diffraction analysis and electron paramagnetic resonance measurement. Then, the target anions [M(1)Au(37)(PET)(24)](−) were obtained by reducing [M(1)Au(37)(PET)(24)](0) with NaBH(4), and isoelectronicity with [Au(38)(PET)(24)](0) was confirmed by optical spectroscopy and density functional theory calculations. Finally, anion PES on [M(1)Au(37)(PET)(24)](−) observed two distinctive peaks as predicted by the SVB model: one from the nearly degenerate 1Π* orbitals and the other from the nearly degenarate 1Π and 2Σ orbitals.