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

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

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(n>6)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.

Using B3LYP/6-311＋G method,the initial geometrical structures of boron-carbon clusters C2＋nB10-n（n=0～10） containing double planar pentacoordinate carbon （ppC） were optimized and their vibrational 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 molecules include double ppCs and ppCs obey octal rule;the C 2＋n B 10-n （n=3～6） clusters with the lowest energy contain one ppC,while the lowest energy C 2＋n B 10-n （n6） 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 of π 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 aromaticity 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.