Theovetical Study of Silicon Clusters and Metal-Containing Carbon Clusters

1. 硅团簇和含硅碳团簇对于Si_n （n=1-20）和SiC_n （n=2-5）团簇，研究了其结构和电子态随尺寸(n)的增加而发生的变化。(1)为了揭示其有趣的性质，研究了将金属原子封装在空心碳团簇（富勒烯）内。通过理论计算M@C_<82>, Sc_2 @C_<84>, M_2 @C_<80> (M=Sc， Y,La, Ce, Pr, Eu, Gd, Yb, Lu)，公开如下：(a)电子态与被包覆金属原子的种类密切相关；(b)两到三个电子从金属转移到碳笼；(c)即使增加或除去一个电子，金属上的净电荷也几乎没有变化，内面金属富勒烯被认为是一种“超原子”；(d)内面金属富勒烯可以作为更强的电子受体和供体。(e)内嵌金属掺杂导致了有趣的反应，这与空情况有很大的不同。Sc_2 @C_<84>和La_2 @C_<80>的首次结构测定尤其值得注意，因为它对生长机制提供了新的认识。这些结构是在最后的退火过程中确定的，具有较大HOMO-LUMO间隙的能量稳定异构体产生和提取最多。(2)研究了Sc_2 @C_<84>和La_2 @C_<80>对包埋金属的动力学行为。研究发现，即使在室温下，两个Sc原子的振荡幅度较大，而两个La原子的振荡幅度较大。两个La^<3+>原子的圆周运动也通过实验观察了^<13>C和^<139>La核磁共振波谱，并有望提供一个有趣的具有新的电子和磁性质的分子器件。

1. Silicon clusters and silicon-containing carbon clustersFor the Si_n (n=1-20) and SiC_n (n=2-5) clusters, it has been investigated how the structures and electronic states change as the size (n) increases.2. Spherical carbon clusters containing transition metal atoms(1) Encapsulation of metal atoms insides hollow carbon clusters (fullerenes) has been investigated in order to disclose the interesting properties. Through the theoretical calculations of M@C_<82>, Sc_2 @C_<84>, and M_2 @C_<80> (M=Sc, Y,La, Ce, Pr, Eu, Gd, Yb, and Lu), the following has been disclosed ; (a) the electronic sates depend strongly on the kind of encapsulated metal atoms, (b) two or three electrons are transferred from metals to carbon cages, (c) the net charge on metals are little changed even when an electron is added or removed, endohedral metallofullerene being regarded as a sort of "superatom" , (d) endohedralmetallofullerene can act as stronger electron acceptors and donors, and (e) endohedral metaldoping leads to interesting reactivities which differ significantly from those of the empty cases. The first structural determination of Sc_2 @C_<84> and La_2 @C_<80> is especially noteworthy since it provides new insight into the growth mechanism. It has been suggested that the structures are determined during the final annealing process and energetically stable isomers with a large HOMO-LUMO gap are most abundantly produced and extracted.(2) To disclose the dynamic behavior of entrapped metals, Sc_2 @C_<84> and La_2 @C_<80> have been investigated in detail. It has been found that the two Sc atoms are oscillating with considerable amplitude while the two La atoms are circulating at high speed even at room temperature. The circular motion of two La^<3+> atoms has also been experimentally by observing the ^<13>C and ^<139>La NMR spectra and is expected to provide an interesting molecular device with new electronic and magnetic properties.