包含两个平面五配位碳原子C_(2+n)B_(10-n)(n=0～10)团簇的结构的理论研究

采用B3LYP/6-311+G**方法,我们优化了初始构型中包含两个平面五配位碳原子(ppCs)的C2+nB10-n(n=0～10)团簇的结构并计算了它们的振动频率.计算结果表明,C2+nB10-n(n=0～2)团簇是稳定的,而且这三个结构中ppC—B键的Wiberg键级介于0.511～0.909之间,ppC—C键的Wiberg键级为0.2254(n=1)和0.8586(n=2),ppC的键级介于3.778到3.879之间,即这三个结构中存在两个ppCs,而且ppC遵循八隅规则;C2+nB10-n(n=3～6)团簇的最稳定结构包含一个ppC;C2+nB10-n(n6)团簇能量最低结构中不存在ppC.而且只有团簇C2+nB10-n(n=0～2)中没有悬键,它们的π电子数分别为:6,7和8,计算它们的NICS(0)值表明强芳香性一般位于局部的三元环中心,表明局部离域有利于平面结构的形成.C2+nB10-n(n=0～2)团簇的第一垂直激发能分别为:1.91,0.56和3.12eV.

Theoretical Study of the Structures of C_(2+n)B_(10-n) (n=0～10) Cluster with Two Planar Pentacoordinate Carbons

Using B3LYP/6-311 +G~(**) method, the initial geometrical structures of boron-carbon clusters C_(2+n)B_(10-n) (n=0～10) containing double planar pentacoordinate carbon (ppC) were optimized and their vi-brational frequencies were calculated. Present results showed that C_(2+n)B_(10-n) (n = 0～2) clusters are stable, in which the Wiberg bond index (WBI) of ppC-B bonds are between 0.511 and 0.909 and the WBIs of ppC-C are 0.2254 (n=1) and 0.8586 (n=2), as well as the WBIs of ppC are 3.778 and 3.879, i.e. the three mole-cules include double ppCs and ppCs obey octal rule; the C_(2+n)B_(10-n) (n=3～6) clusters with the lowest en-ergy contain one ppC, while the lowest energy C_(2+n)B_(10-n) (n>6) clusters have no ppC. In addition, only the C_(2+n)B_(10-n) (n=0～2) clusters do not include dangling bonds, and the numbers ofπ electron in the C_(2+n)B_(10-n) (n=0～2) clusters are 6, 7 and 8, respectively. Calculated NICS(0) values indicate that the strong aromatic-ity mainly locates at the centers of the three-membered rings. The vertical transition energies of C_(2+n)B_(10-n) (n=0～2) clusters are 1.91, 0.56 and 3.12 eV.