Structures, Properties, and Growth Process of Endohedral Metallofullerenes

1. 内嵌金属富勒烯的结构、电子态和成键特征单金属富勒烯的内嵌结构M@C_<82>(M=Ca, Sc.Y。La, Ce, Pr, Nd, Eu, Gd， Yb和Lu)和二金属富勒烯Sc_2@C_<84>和La_2@C_<80>通过理论预测和实验的密切相互作用揭示。此外，本文还对金属富勒烯的电子密度及其拉普拉斯函数进行了拓扑分析，揭示了金属富勒烯化学键合的一般特征。三金属富勒烯Sc_3@C_<82>的结构和键合研究仍在进行中。封装金属原子的动力学行为通过La_2@C_<80>的13CNMR变温测量，首次发现两个La原子即使在室温下也能在圆形C_<80>笼内带+3电荷循环。这一发现也被变温139La核磁共振测量和理论计算所证实。内嵌金属富勒烯的非常规笼形结构金属原子可以在生长和退火过程中稳定违反富勒烯化学中建立的孤立五边形规则并包含七方环（因此不符合富勒烯的传统定义）的非常规结构。作为代表性的例子，Ca@C_<72>和Sc_2@C_<74>已经证明了这一点。内源性金属掺杂杂富勒烯。用一个氮原子代替La@C_<82>和La_2中的一个笼形碳，制备了La@C_<81>N和La_2@C_<79>N。值得注意的是，与C_<81>N和C_<79>N不同，这些la掺杂的杂富勒烯在笼上没有明显的自由基特征。金属富勒烯的笼形结构不一定与最稳定的富勒烯异构体一致，因为金属笼向碳笼的电子转移非常明显。最可能的是，在退火过程中形成了内腔结构。

1. Structures, Electronic States, and Bonding Features of Endohedral MetallofullerenesThe endohedral structures of monometallofullerenes M@C_<82>(M=Ca, Sc.Y.La, Ce, Pr, Nd, Eu, Gd, Yb, and Lu) and dimetallofullerenes Sc_2@C_<84> and La_2@C_<80> have been disclosed through a close interplay between theoretical prediction and experiment. In addition, a topological analysis of electron density and its Laplacian has been carried out to reveal the general features of chemical bonding in metallofullerenes. The structural and bonding study of the trimetallfullerene Sc_3@C_<82> is still in progress.2. The Dynamic Behaviors of Encapsulated Metal AtomsFrom the variable-temperature 13CNMR measurement of La_2@C_<80>, it has been for the first time found that the two La atoms circulate with +3 charge inside the round C_<80> cage even at room temperature. This finding has been also confirmed by the variab1e-temperature 139La NMR measurement and theoretical calculations.3. Unconventional Cage Structures of Endohedral MetallofullerenesMetal atoms can stabilize unconventional structures which violate the isolated pentagon rule established in fullerene chemistry and contain heptagonal rings (thereby not obeying the traditional definition of fullerenes), during growth and annealing processes. This has been shown for Ca@C_<72> and Sc_2@C_<74>, as representative examples.4. Endohedrallly Metal-Doped Heterofullerenes.An experimental attempt to substitute one cage carbon in La@C_<82> and La_2 by one nitrogen atom has been performed to prepare La@C_<81>N and La_2@C_<79>N.it is noteworthy that these La-doped heterofullerenes have no significant radical character on the cages, unlike C_<81>N and C_<79>N.5. SummaryThe cage structures of metallofullerenes do not necessary coincide with those of the most stable fullerene isomers, because of significant electron transfer from metal to carbon cages. Most Probably, endohedral structures are formed during the annealing process.