Department of Chemistry and Biochemistry, University of Southern Mississippi, 118 College Drive #5043, Hattiesburg, Mississippi 39406, USA.
J Am Chem Soc. 2009 Dec 16;131(49):17780-2. doi: 10.1021/ja908370t.
We report the synthesis and electronic stabilization of La(3)N@C(79)N. Unsuccessful efforts to encapsulate bulky La(3)N clusters in small C(80) cages have been attributed to large ionic radii. The preferred species for La(3)N clusters in all-carbon cages is La(3)N@C(96). A surprising finding is the synthesis of La(3)N@C(79)N, a new metallofullerene present in higher abundance than La(3)N@C(96). This reduction in cage size from 96 to 80 atoms reflects the significance and role of electronic effects. To understand the geometric and electronic properties of this first metallic nitride azafullerene (M(3)N@C(79)N, M = La), density functional theory (DFT) investigations were performed on a number of isomers. Results indicate a preferred N-substitution at the 665 junction site on the cage in lieu of a 666 substitution. The relative stabilities of different isomers can be well reproduced by using the minimum distance between the metal atom and the nitrogen atom of the cage (R(N'M)(min)). Long R(N'M)(min) values indicate distant contacts between six atoms that bear significantly large positive charges: the three metal atoms and the three carbon atoms bonded with the nitrogen atom in the cage, which are favored. These results suggest a dominant electronic effect on the stabilities of metalloazafullerenes. Interestingly, spin densities of the 665 substitution isomers of La(3)N@C(79)N are located predominantly in the metal cluster, while spin densities of the 666 substitution isomers are primarily on the cage.
我们报告了 La(3)N@C(79)N 的合成和电子稳定化。将大块 La(3)N 簇封装在小 C(80)笼中不成功的原因归因于较大的离子半径。对于所有碳笼中的 La(3)N 簇,首选的物种是 La(3)N@C(96)。一个令人惊讶的发现是合成了 La(3)N@C(79)N,这是一种新的金属富勒烯,其丰度高于 La(3)N@C(96)。笼原子尺寸从 96 减少到 80 反映了电子效应的重要性和作用。为了了解这种第一个金属氮化物氮杂富勒烯(M(3)N@C(79)N,M = La)的几何和电子性质,对许多异构体进行了密度泛函理论(DFT)研究。结果表明,在笼上的 665 连接点处优先进行 N 取代,而不是 666 取代。通过使用金属原子和笼氮原子之间的最小距离(R(N'M)(min))可以很好地再现不同异构体的相对稳定性。较大的 R(N'M)(min) 值表明,六个原子之间存在明显大的正电荷的远距离接触:三个金属原子和三个与笼中氮原子键合的碳原子,这是有利的。这些结果表明电子效应对金属氮杂富勒烯的稳定性有很大的影响。有趣的是,La(3)N@C(79)N 的 665 取代异构体的自旋密度主要位于金属簇中,而 666 取代异构体的自旋密度主要在笼上。