論文リスト

学術論文 2015

Synthesis and Catalytic Application of Ag44 Clusters Supported on Mesoporous Carbon

Masaru Urushizaki, Hirokazu Kitazawa, Shinjiro Takano, Ryo Takahata, Seiji Yamazoe, and Tatsuya Tsukuda*
J. Phys. Chem. C 119, 27483-27488 (2015).

4-(Fluorophenyl)thiolate-protected Ag44 clusters (Ph4P)4[Ag44(SC6H4F)30] were calcined on mesoporous carbon (MPC) under a vacuum at 300-500 ℃ for 2 h. X-ray absorption spectroscopy, transmission electron microscopy, and thermal-desorption mass spectrometry revealed that sulfur-free Ag44 clusters were successfully produced by calcination of [Ag44(SC6H4F)30]4− at 300 ℃, in sharp contrast to the formation of silver sulfide nanoparticles by calcination of dodecanethiolate-protected Ag nanoparticles (3.0 ± 0.6 nm). The Ag44/MPC was applied for catalytic dehydrogenation of ammonia-borane (NH3BH3) as a test reaction. It turned out that the Ag44/MPC catalysts produced one equivalent of H2 from NH3BH3, but only in the presence of O2 (turnover frequency; 1.9 × 103 h−1 Ag atom−1). Given that nanoparticles of other metals (Pt, Pd, Rh, Ni, or Ru) produced three equivalents of H2 under an inert atmosphere, this result indicates that the Ag44/MPC-catalyzed dehydrogenation of NH3BH3 proceeds by a different mechanism from that on other nanoparticles.

Slow-reduction Synthesis of a Thiolate-protected One-dimensional Gold Cluster Showing an Intense Near-infrared Absorption

Shinjiro Takano, Seiji Yamazoe, Kiichirou Koyasu, and Tatsuya Tsukuda*
J. Am. Chem. Soc. 137, 7027-7030 (2015).

Slow reduction of Au ions in the presence of 4-(2-mercaptoethyl)benzoic acid (4-MEBA) gave Au76(4-MEBA)44 clusters that exhibited a strong (3 × 105 M−1cm−1) NIR absorption band at 1340 nm. Powder X-ray diffraction studies indicated that the Au core has a one-dimensional fcc structure that is elongated along the {100} direction.

Density Functional Theory Study on Stabilization of Al13 Superatom by PVP

Tomomi Watanabe, Kiichirou Koyasu, and Tatsuya Tsukuda*
J. Phys. Chem. C 119, 10904-10909 (2015).

The sequential bonding of N-ethyl-2-pyrrolidone (EP), a monomer unit of poly(vinylpyrrolidone) (PVP), to an open-shell superatom Al13 was studied by density functional theory calculations. The first three EP ligands prefer to be chemisorbed on the atop sites of Al13 via the carbonyl O atom mainly due to bonding interaction between molecular orbitals of EP and the 1S or 1D superatomic orbital of Al13. The fourth EP ligand, however, prefers to be bound electrostatically to one of the chemisorbed EP ligands rather than to be chemisorbed on Al13. This behavior suggests that the maximum number of PVP that can be chemisorbed on Al cluster is determined not only by the steric repulsion between adjacent PVP but also by the electronic charge accumulated on the Al cluster. The gross Mulliken charge accumulated on the Al13 moiety increases with the number of EP ligands chemisorbed and reaches nearly -1 e in Al13(EP)3, suggesting the closure of the electronic shell of Al13 by ligation of three EP ligands. However, the spin density analysis revealed that the superatomic orbital 1F of Al13 remains singly occupied even after chemisorption of three EP ligands. In conclusion, the Al13 moiety stabilized by PVP remains to be an open-shell superatom although it accepts electronic charge through polarized Al-O bonding.

A Critical Size for Emergence of Nonbulk Electronic and Geometric Structures in Dodecanethiolate-Protected Au Clusters

Yuichi Negishi*, Tafu Nakazaki, Sami Malola, Shinjiro Takano, Yoshiki Niihori, Wataru Kurashige, Seiji Yamazoe, Tatsuya Tsukuda*, and Hannu Häkkinen*
J. Am. Chem. Soc. 137, 1206-1212 (2015).

We report on how the transition from the bulk structure to the cluster-specific structure occurs in n-dodecanethiolate-protected gold clusters, Aun(SC12)m. To elucidate this transition, we isolated a series of Aun(SC12)m in the n range from 38 to ~520, containing five newly-identified or newly-isolated clusters, Au104(SC12)45, Au~226(SC12)~76, Au~253(SC12)~90, Au~356(SC12)~112, and Au~520(SC12)~130, using reverse-phase high-performance liquid chromatography. Low-temperature optical absorption spectroscopy, powder X-ray diffractometry, and density functional theory calculations revealed that the Au cores of Au144(SC12)60 and smaller clusters have molecular-like electronic structures and non-fcc geometric structures, whereas the structures of the Au cores of larger clusters resemble those of the bulk gold. A new structure model is proposed for Au104(SC12)45 based on combined approach between experiments and DFT calculations.

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