Fullerenes Violating the Isolated Pentagon Rule

Abstract

Fullerenes are cage-shaped carbon clusters. Compared with the vast number of theoretically possible fullerene isomers, only quite a few of them were obtained experimentally. It is due to the constraint of the isolated pentagon rule (IPR), which states that the fullerenes with isolated pentagons are stable, otherwise they are instable. The adjacent pentagons have unfavorable antiaromaticity and local strain. In terms of endohedral and exohedral derivatization, fullerenes with adjacent pentagons can be stabilized. Following these stabilization principles, the synthetic routes to non-IPR fullerenes nowadays include the metal-doped arc discharge, chlorine or hydrogen-involved arc discharge, low-pressure combustion, chlorine-involved radio frequency furnace, and postfunctionalization-promoted cage transformation. Based on these methods, more than 60 members of non-IPR fullerenes were synthesized and characterized from C20 to C102. These non-IPR fullerenes are vital for understanding the mechanism of fullerene formation, but also provide novel basic building blocks for fullerene materials. Based on the structures of prepared non-IPR fullerenes, the stabilization of fused pentagons was well understood, which can guide the synthesis of non-IPR fullerenes in the future. After the decades of research, the non-IPR fullerenes have been a hot field in the fullerene science.KeywordsFused pentagons-stabilizationDerivatizationChlorinationHydrogenationEndofullereneAromaticity