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

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, C₂B₁₂H₁₄碳硼烷的9个异构体都有对应的稳定构型, 并基本保持了B₁₄H₁₄^2－的骨架构型; 除两个C原子取代轴顶点位置B原子的1,14-C₂B₁₂H₁₄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.

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

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 C_2B_(12)H_(14) isomers were obtained and their molecular backbone structures remained that of B_(14)H_(14)~(2-) Besides the stability of 1,14-C_2B_(12)H_(14) with two C atoms substituted for B atoms in axial position,the stabilities in- crease 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 dis- tributed 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 en- ergy levels of the isomers is coincided with their stabilities,and the isomer having lower HOMO energy level is more stable.