Formation and Electronic Structures of Organoeuropium Sandwich Nanowires

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• 作者：Natsuki Hosoya ; Ryuta Takegami ; Jun-ichi Suzumura ; Keizo Yada ; Ken Miyajima ; Masaaki Mitsui ; Mark B. Knickelbein ; Satoshi Yabushita ; Atsushi Nakajima
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：September 18, 2014
• 年：2014
• 卷：118
• 期：37
• 页码：8298-8308
• 全文大小：778K
• ISSN：1520-5215

文摘

Organoeuropium sandwich clusters, comprising europium (Eu) and 1,3,5,7-cyclooctatetraene (COT) (Eu_n(COT)_m), were produced in the gas phase using a laser vaporization synthesis method. Photoionization mass spectra revealed an exclusive Eu_n(COT)_m formation with three compositions: m = n + 1, m = n, and m = n 鈥?1, which, we propose, correspond to full-sandwich, half-sandwich, and inverted-sandwich structures, respectively. The charge distributions, metal鈥搇igand bonding characteristics, and electronic structures of the clusters were comprehensively investigated by photoionization measurements of Eu_n(COT)_m neutrals and by photoelectron spectroscopy of Eu_n(COT)_m^{鈥?/sup> and isoelectronic Ba_n(COT)_m鈥?/sup> anions. The results confirmed that (1) highly ionic metal鈥搇igand bonding is formed between Eu2+ and COT2鈥?/sup> within the sandwich structure (at the termini, ionic forms are Eu+ and COT鈥?/sup>) and (2) size dependence of orbital energy can be explained by the Coulombic interaction of simple point charge models between the detaching electrons and dipoles/quadrupoles. When the terminus of the sandwich clusters is Eu2+, COT2鈥?/sup>, or Eu0, the orbital energy of the electron detachment channel at the opposite terminus strongly depends on the cluster size. In this case, the molecular stack behaves as a one-dimensionally aligned dipole; otherwise, it behaves as a quadrupole, and the relationship between cluster size and electron detachment energy is much weaker. The study also reports on the 4f orbital energy in Eu ions and the formation mechanism of organoeuropium sandwich nanowires up to 12 nm in length. The nanowires are formed by successive charge transfer at the terminal part, Eu+ and COT鈥?/sup>, which reduces the ionization energy and increases the electron affinity, respectively.}