14顶点闭合型碳硼烷异构体的结构和稳定性的密度泛函理论研究

Density Functional Theory Study on the Structures and Stabilities of 14-Vertex closo-Carborane Isomers

采用密度泛函理论(DFT)B3LYP/6-31G(d)方法对14顶点闭合型碳硼烷异构体的几何结构进行优化,分析了它们的稳定性、电荷分布以及前线分子轨道能级．结果表明,C_2B_(12)H_(14)碳硼烷的9个异构体都有对应的稳定构型,并基本保持了B_(14)H_(14)^(2-)的骨架构型;除两个C原子取代轴顶点位置B原子的1,14-C_2B_(12)H_(14)外,其稳定性均随着两个C原子之间距离的增大而增加,但C原子取代高配位数的B原子不利于其构型的稳定性．各异构体的负电荷主要分布在C原子上,同时处于轴向位置的B原子也有部分负电荷,它们可能成为反应的亲核活性中心．异构体的HOMO能级的高低与其稳定性相对应,HOMO能级低的异构体稳定性好．

This paper employed density functional theory （DFT） B3LYP method to optimize the structures of 14-vertex closo-carborane clusters at 6-31G（d） level and the stabilities, charge distributions and energy levels of frontal molecular orbital were analyzed. The results indicated that the stable structures of nine C2B12H14 isomers were obtained and their molecular backbone structures remained that of B14H14^2-. Besides the stability of 1,14-C2B12H14 with two C atoms substituted for B atoms in axial position, the stabilities increase with the increasing of distances between the two C atoms. The substitution of C atoms for B atoms in the higher coordination number position decreases the stability. The negative charge of each isomer is distributed mainly among the C atoms and the rest is among the axial B atoms, and the positions of C atoms and the axial B atoms may become the active regions of the nucleophilic reaction. The trend of HOMO energy levels of the isomers is coincided with their stabilities, and the isomer having lower HOMO energy level is more stable.