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 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.