nido-C_2B_9H_(11)^(2-)碳硼烷异构体结构和稳定性的密度泛函研究

Density functional theory study on the structures and stabilities of nido-C_2B_9H_(11)^(2-) carborane isomers

采用密度泛函方法对11顶点巢式碳硼烷C2B9H112-异构体进行了几何结构优化,分析了稳定性、电荷分布及分子轨道.结果表明,9个异构体都有对应的稳定构型,保持了巢式骨架结构.C取代开口五元环上B的异构体更稳定,且随取代数目增加和C原子间距增加而增加,C—C键和C—B键作用增强.C取代内层B使异构体稳定性降低,C—C键和C—B键长随之增长.负电荷主要集中在C原子上,开口五元环上的C原子上负电荷要比内层C原子更多,成为亲核取代反应中心.异构体分子前线轨道具有和η5-C5H5-相似的π键性质,ΔELUMO-HOMO反映的化学稳定性与结构能量稳定性趋势一致.

This paper employed density functional theory（DFT）method to optimize the structures of 11-vertex nido-C2B9H112-carborane clusters at DNP level.The stabilities,charge distributions and energy levels of fontal molecular orbital were analyzed.The results indicated that the stable structures of nine C2B9H112-isomers were obtained and their molecular backbone structures remained that of B11H114-.The substitution of C atoms for B atoms in the open five-member rings position increases the isomer stability.The isomer stabilities increase with the increasing of distances between the two C atoms.The negative charge of each isomer is distributed mainly among the C atoms,which may become the active regions of the nucleophilic reaction.The tend of energy gap between frontier orbitals is coincided with their stabilities.