C_(80)X_(12)(X=H,F,Cl,Br)的结构和稳定性

Theoretical study on the structures and stability of C_(80)X_(12)(X=H,F,Cl,Br)

为了考察勒烯衍生物结构与稳定性关系,采用密度泛函理论方法对C80X12(X=H,F,Cl,Br)进行了系统计算究.结表明,在C80X12(X=H,F)异构体中,最低能量异构体都违反五元环分离规则.然而,在C80X12(X=Cl,Br)异构体中,最低能量异构体都满足五元环分离规则.由于van der Waals半径较小,H或F加成到碳笼上时外部原子之间排斥作用小,因此在其优结构中,H或F优先加成到2个五元环共用碳原子上.相反,对于氯化、溴化勒烯,为了避免外部加成原子之间在重空间排斥作用,其优结构中Cl或Br优先加成到1,4-位点上.计算结还显,氢化、卤化反应热(C80+6X2→C80X12)遵循如下顺序,即C80F12>C80Cl12>C80H12>C80Br12.这些结表明勒烯衍生物稳定性和衍生化模与加成原子尺和电性有关.

Density functional theory calculations were performed on C80X12（X=H,F,Cl,Br） to gain insight into their structures and stability.The results demonstrate that the lowest energy isomers are IPR-violating for C80X12（X=H,F）,however,for C80X12（X= Cl,Br）,the lowest energy isomers are IPR-satisfying.Since the van der Waals radius of H and F atoms are small,the resulting steric strain among added atoms is slight or negligible for C80X12（X=H,F）,and thus the lowest energy structures are those with the H and F atoms bonded to the carbon atoms of the fused pentagons.However,Cl and Br atoms tend to bond to 1,4-cites to avoid strong steric repulsion.The calculated results also reveal that the order of the energy of reaction C80 ＋6X2 →C80X12 （X=H,F,Cl,Br） is C80F12 C80Cl12 C80H12 C80Br12.These results suggest that the stability and addition patterns of fullerene derivatives are also related to the radius and electronegativity of added atoms.