内嵌镧金属富勒烯的高产率合成及异构体比例调控

采用电弧放电法制备内嵌镧金属富勒烯的原灰,通过改变氦气压力及电流强度来提高内嵌镧金属富勒烯产率。原灰由1,2,4-三氯苯提取并回溶入甲苯后,利用分析型高相液相色谱（HPLC）对提取液中各富勒烯组分进行分析。通过分别衡量3种常见含镧金属富勒烯La@C_2v-C₈₂、La@C_s-C₈₂和La₂@C₈₀与C₈₄的相对峰面积比,探讨了氦气压力和电流强度等对3种金属富勒烯产率的影响。实验结果表明,氦气压力与电流强度共同决定了金属富勒烯的产率,在（1）低电流高氦气压、（2）中等电流中等氦气压、（3）高电流低氦气压的条件下都可以高产率地获得含镧金属富勒烯。此外,调整电流强度和氦气压力可以改变La@C_2v-C₈₂和La@C_s-C₈₂的相对比例。例如,在电流为100、120 A或氦气压为20、35 kPa时,此前认为的"minor"异构体La@C_s-C₈₂的含量甚至高于"major"异构体La@C_2v-C₈₂。我们还发现,降低电流强度或减小氦气压力可促进La₂@C₈₀的生成,这表明La₂@C₈₀与La@C₈₂的形成过程可能是不同的。

High-Yield Synthesis and Isomeric Ratio Control of La Endohedral Metallofullerenes

La-containing metallofullerenes were synthesized with a direct current arc-discharge method, and the experimental conditions such as helium pressure and current density were optimized to improve the yield of metallofullerenes (La@C_2v-C₈₂, La@C_s-C₈₂ and La₂@C₈₀). The raw soot was extracted by 1,2,4-trichlorobenzene and was then redissolved in toluene. The yields of the La-containing metallofullerenes were discussed based on the high performance liquid chromatographic results by comparing their peak areas with that of C₈₄. Experimental results show that the high yield of La@C₈₂ can be attributed to a synergetic effect of current density and He pressure, i.e. (1) low current and high He pressure; (2) medium current and medium He pressure; and (3) high current and low He pressure. Furthermore, the relative ratio of La@C_2v-C₈₂ and La@C_s-C₈₂ can be adjusted by changing the current density and He pressure. Surprisingly, it is discovered that low current density or low He pressure facilitates the formation of La₂@C₈₀, indicating that the formation process of La₂@C₈₀ may be different from that of La@C₈₂.