富勒烯[4,6]-C_(24)的BN取代物的结构及其稳定性的理论研究

DFT(Density Functional Theory) Studies on Structures and Stabilities of C_(24-2x)(BN)_x(x=1～12) Isomers

用密度泛函方法，在B3LYP／6-31G（d）理论水平上优化了由四元环与六元环构成的富勒烯C24的所有BN取代物的构型，分析了各异构体相对稳定性与杂原子取代位置间的关系；对各异构体进行了频率分析，计算了C24-2x（BN）x（X=1-12）最稳定异构体的正则振动模式。结果表明：BN取代共边六元环公共边上的碳原子所得C22BN为最稳定的单BN取代物，C22BN各异构体的稳定性主要由体系的共轭性质决定；而富勒烯C24的多BN取代物的稳定性主要由环张力决定，也受体系的共轭性质影响，能量数据表明随着BN取代单元的增加，C24-2x（BN）x的稳定性增强，并且振动光谱变得更简单，吸收增强。

Density functional theory （B3LYP/6-31G（d）） is applied to optimize all the possible stable struc-tures of BN-substituted fullerenes C24 with frequency analysis. The relationship between the stabilities of the C24-2x（BN）x isomers and the sites where boron or nitrogen atoms dope at the C24 cage has been examined. The normal vibration modes of the most stable isomers of C24-2x（BN）x are analyzed. The most stable C22 BN isomer is formed by boron and nitrogen doping at the common edge of the two neighboring hexa-gons, and the stabilities of the C22 BN isomers are mainly determined by the conjugate effect of the cage, while the stabilities of the C24-2x （BN）x（x= 2-12） isomers are mainly determined by ring tension and, to a smaller extent, by the nature of the conjugated system. The energy data indicate that as the number of the BN substitution units increases, the stability of the C24-2x（BN）x（x=2-12） isomers enhances, and the vibrational spectrum becomes simpler and stronger.