Grubisic Andrej, Ko Yeon Jae, Wang Haopeng, Bowen Kit H
Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA.
J Am Chem Soc. 2009 Aug 5;131(30):10783-90. doi: 10.1021/ja805205r.
Photoelectron spectroscopy was utilized to study a variety of LnSi(n)(-) cluster anions (Ln = Yb, Eu, Sm, Gd, Ho, Pr; 3 <or= n <or= 13). For a particular size n, the measured valence electronic transitions of all these systems fall into either one of two categories, reflecting the influence of the different oxidation states of the lanthanide atoms involved. In one, the spectra of YbSi(n)(-) and EuSi(n)(-) are nearly identical to each other, while in the other the spectra of GdSi(n)(-), HoSi(n)(-), and PrSi(n)(-) are essentially identical. SmSi(n)(-) clusters exhibit an intermediate behavior with smaller clusters resembling the former category and larger clusters resembling the latter category. In the intermediate size range, 7 <or= n <or= 10, for SmSi(n)(-) both categories appear to be present, with one matching the EuSi(n)(-)-like systems and the other HoSi(n)(-)-like clusters. The distinction between LnSi(n)(-) categories strongly correlates with the oxidation state of the particular lanthanide as usually found in its compounds. On the basis of this observation, we conclude that, among the Ln-silicon clusters studied herein, Yb, Eu, and in case of Sm, sizes n >or= 10, adopt a nominal +2 oxidation state while Ho, Pr, Gd, and in case of Sm, sizes n <or= 7, exhibit a nominal +3 oxidation state. Furthermore, dramatic increases in adiabatic electron affinity values observed at n = 10 for the Ln(III)Si(n) series and at n = 12 for the Ln(II)Si(n) series were attributed to an inherent electronic stabilization of those particular clusters, rather than to the lanthanides' encapsulation. The observed limited effect of f-electrons on the valence electronic structure and thus on bonding in LnSi(n)(-) clusters may leave these electrons available for inducing magnetism. Consequently, Ln@Si(n) clusters may hold promise as building blocks of silicon-based cluster materials with magnetic properties.
利用光电子能谱研究了多种LnSi(n)(-)团簇阴离子（Ln = Yb、Eu、Sm、Gd、Ho、Pr；3≤n≤13）。对于特定的尺寸n，所有这些体系测得的价电子跃迁可分为两类，这反映了所涉及镧系原子不同氧化态的影响。一类中，YbSi(n)(-)和EuSi(n)(-)的光谱彼此几乎相同，而另一类中，GdSi(n)(-)、HoSi(n)(-)和PrSi(n)(-)的光谱基本相同。SmSi(n)(-)团簇表现出中间行为，较小的团簇类似于前一类，较大的团簇类似于后一类。在中间尺寸范围7≤n≤10内，SmSi(n)(-)两类行为似乎都存在，一类与EuSi(n)(-)类体系匹配，另一类与HoSi(n)(-)类团簇匹配。LnSi(n)(-)类别之间的差异与特定镧系元素在其化合物中通常的氧化态密切相关。基于这一观察结果，我们得出结论，在本文研究的Ln-硅团簇中，Yb、Eu以及Sm尺寸n≥10时采用名义上的+2氧化态，而Ho、Pr、Gd以及Sm尺寸n≤7时表现出名义上的+3氧化态。此外，对于Ln(III)Si(n)系列在n = 10时以及Ln(II)Si(n)系列在n = 12时观察到的绝热电子亲和能值的显著增加，归因于这些特定团簇固有的电子稳定性，而非镧系元素的包裹。观察到f电子对价电子结构进而对LnSi(n)(-)团簇中键合的影响有限，这可能使这些电子可用于诱导磁性。因此，Ln@Si(n)团簇有望成为具有磁性的硅基团簇材料的构建单元。
