Theoretical Study On Structures And Stabilities Of [4, 6]-Fullerenes And The BN-Deriviatives

In present paper, we applied density functional theory (B3LYP) to systematically investigate the relationship between structures and stabilities of [4,6] - fullerenes C₂₄, C₃₂ and their BN-derivatives, and obtained some substitution rules of [4,6] - fullerenes by boron and nitrogen. Using AM1 methods, we also studied the [4,6]-fullerenes, (C₂₄)_n(n=1,2,4,8) and their BN-derivatives, and discussed the changes of their structures and stabilities. This paper includes the following three parts.1. Density functional theory (B3LYP/6-31G(d)) is applied to optimize all the possible stable structures of BN-substituted fullerenes C₂₄ with frequency analysis. The relationship between the stabilities of the C_24-2x(BN)_x isomers and the sites where boron or nitrogen atoms dope at the C₂₄ cage has been examined. In addition, the vibration modes of the most stable isomers of C_24-2x(BN)_x are analyzed. The most stable C₂₂BN isomer is formed by boron and nitrogen doping at the common edge of the two neighboring hexagons, the stabilities of the C22BN isomers are mainly determined by the conjugate effect of the cage; while the stabilities of the C_24-2x(BN)_x(x=2～12) isomers are mainly determined by ring tension, also affected 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 C_24-2x(BN)_x (x=2-12) isomers enhances, and the vibrational spectrum becomes simpler and stronger.2. Density functional theory (B3LYP/6-31G) is applied to optimize single and double BN-substituted products of [4,6]-C₃₂ fullerene with frequency analysis. The results show that the most stable C₃₀BN isomer is formed by boron and nitrogen doping at the common edge of the neighboring hexagon and quadrangle, the stabilities of the C₃₀BN isomers are mainly determined by the ring tension, and also affected by the nature of the conjugated system; and that the most stable of the C₂₈(BN)₂ isomers is the one in which the two BN units connects to each other head-to-end to form a tetragon, and the stability of the system are mainly determined by ring tension. The substitution rules of [4,6]-C₃₂ and C₂₄ are different form each other.3. AM1 semi-empirical quantum chemical method is applied to optimize the fullerene [4,6]-(C₂₄)_n(n =1,2,4,8) and their BN-substituted products [4,6]-((BN)₁₂)_n(n =1,2,4,8) with frequency analysis. The results show that the carbon fullerenes and the BN clusters show similar rules of the stability with the changes of the symmetry; BN substitution enhances the stability of the system, so the BN clusters may be expected to be prepared in the laboratory; from the charge distribution of the cluaters we can predict the active site of the molecules to take part in chemical reaction in laboratory.