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.

Au(PET) (PET = SCHPh) is known to have a bi-icosahedral Au core consisting of two Au 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 core is similar to that in the F molecule. The SVB model predicted that the electron configuration of the Au core with 14 valence electrons is expressed as (1Σ)(1Σ*)(1Π)(2Σ)(1Π*) where each orbital is created by the bonding and antibonding interactions between the 1S and 1P superatomic orbitals of the icosahedral Au units. Therefore, the bi-icosahedral Au can be viewed as a di-superatomic molecule. To validate the SVB model, we herein conducted anion photoelectron spectroscopy (PES) on [MAu(PET)] (M = Pd and Pt), which are isoelectronic and isostructural with Au(PET). To this end, the neutral precursors [MAu(PET)] were first synthesized by fusion reactions between hydride-doped clusters [HAu(PPh)] and [MAu(PET)]. The formation of bi-icosahedral MAu cores with open electronic structure in [MAu(PET)] was confirmed by single-crystal X-ray diffraction analysis and electron paramagnetic resonance measurement. Then, the target anions [MAu(PET)] were obtained by reducing [MAu(PET)] with NaBH, and isoelectronicity with [Au(PET)] was confirmed by optical spectroscopy and density functional theory calculations. Finally, anion PES on [MAu(PET)] 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.