Furuse Shunsuke, Koyasu Kiichirou, Atobe Junko, Nakajima Atsushi
Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.
J Chem Phys. 2008 Aug 14;129(6):064311. doi: 10.1063/1.2966005.
Silicon (Si), germanium (Ge), tin (Sn), and lead (Pb) clusters mixed with a group-4 transition metal atom [M = titanium (Ti), zirconium (Zr), and hafnium (Hf)] were generated by a dual-laser vaporization method, and their properties were analyzed by means of time-of-flight mass spectroscopy and anion photoelectron spectroscopy together with theoretical calculations. In the mass spectra, mixed neutral clusters of MSi(16), MGe(16), and MSn(16) were produced specifically, but the yield of MPb(16) was low. The anion photoelectron spectra revealed that MSi(16), MGe(16), and MSn(16) neutrals have large highest occupied molecular orbital-lowest unoccupied molecular orbital gaps of 1.5-1.9 eV compared to those of MPb(16) (0.8-0.9 eV), implying that MSi(16), MGe(16), and MSn(16) are evidently electronically stable clusters. Cage aromaticity appears to be an important determinant of the electronic stability of these clusters: Calculations of nucleus-independent chemical shifts (NICSs) show that Si(16)(4-), Ge(16)(4-), and Sn(16)(4-) have aromatic characters with negative NICS values, while Pb(16)(4-) has an antiaromatic character with a positive NICS value.
通过双激光汽化法生成了与第4族过渡金属原子[M =钛（Ti）、锆（Zr）和铪（Hf）]混合的硅（Si）、锗（Ge）、锡（Sn）和铅（Pb）团簇，并通过飞行时间质谱、阴离子光电子能谱以及理论计算对其性质进行了分析。在质谱中，特别生成了MSi(16)、MGe(16)和MSn(16)的混合中性团簇，但MPb(16)的产率较低。阴离子光电子能谱显示，与MPb(16)（0.8 - 0.9 eV）相比，MSi(16)、MGe(16)和MSn(16)中性团簇具有1.5 - 1.9 eV的大最高占据分子轨道 - 最低未占据分子轨道能隙，这意味着MSi(16)、MGe(16)和MSn(16)是明显电子稳定的团簇。笼状芳香性似乎是这些团簇电子稳定性的一个重要决定因素：核独立化学位移（NICS）计算表明，Si(16)(4-)、Ge(16)(4-)和Sn(16)(4-)具有负NICS值的芳香特征，而Pb(16)(4-)具有正NICS值的反芳香特征。
