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Tatsuya Tsukuda1 2

1, University of Tokyo, Tokyo, , Japan
2, Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Kyoto, , Japan

Gold clusters protected by ligands or stabilized by polymers are viewed as superatoms from the analogy of the electronic structures with those of the conventional atoms. It has been demonstrated that H atom mimics Au atoms in bare Au clusters: the electronic and geometric structures of Au clusters are retained after replacement of the Au atom with H atom [1]. A recent theoretical study proposed that an H atom behaves as an Au atom in the Au cluster Au25(SR)18 (SR = thiolate) and contributes its 1s electron to the superatomic electron count [2]. Small nonplasmonic Au clusters stabilized by polymer exhibit localized surface plasmon resonance in the presence of NaBH4 due to electron donation from the adsorbed H atoms [3,4]. These results suggest that structures and properties of gold superatoms can be tuned through doping H atoms. However, a molecular-level understanding has not been attained about the interaction between H and Au superatoms.
The present work focuses on the interaction of H with phosphine-protected Au-based clusters [Au9(PPh3)8]3+ and [PdAu8(PPh3)8]2+ which can be viewed as oblate gold superatoms with 6 electrons. We observed by mass spectrometry and NMR spectroscopy that a hydride (H) was doped into these gold-based oblate superatoms upon the reaction with NaBH4. Density functional theory calculations of the products [Au9H(PPh3)8]2+ and [PdHAu8(PPh3)8]2+ demonstrated that hydride is bonded to a coordinatively unsaturated site at the center and that the (Au9H)2+ and (PdHAu8)+ core can be viewed as nearly spherical superatom with closed electronic shells. The hydride-doped superatoms (Au9H)2+ was successfully converted to the well-known Au113+ superatoms by the reaction with Au(I) complexes, while the hydride in the (PdHAu8)+ remained during the growth to (PdHAu10)+. These hydride-mediated growth processes will provide a new atomically precise synthesis of Au clusters via bottom-up approach.

[1] Buckart, S.; Ganteför, G.; Kim, Y. D.; Jena, P. J. Am. Chem. Soc. 2003, 125, 14205.
[2] Hu, G.; Tang, Q.; Lee, D.; Wu, Z.; Jiang, D.-e. Chem. Mater. 2017, 29, 4840.
[3] Ishida, R.; Yamazoe, S.; Koyasu, K.; Tsukuda, T. Nanoscale 2016, 8, 2544.
[4]Ishida, R.; Hayashi, S.; Yamazoe, S.; Kato, K.; Tsukuda, T. J. Phys. Chem. Lett. 2017, 8, 2368.

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