Maximum Aromaticity as a Guiding Principle for the Most Suitable Hosting Cages in Endohedral Metallofullerenes

摘要

Fullerenes are a recently discovered carbon allotrope in which carbon atoms are arranged into 12 pentagons and a variable number of hexagons in a more or less spherical shape. The most stable empty neutral fullerenes strictly obey the isolated-pentagon rule (IPR) formulated by Kroto in 1987. This rule states that all pentagons must be surrounded by hexagons to alleviate the strain produced by two fused pentagons (a pentalene unit). The pentagon adjacency penalty rule (PAPR) quantifies the destabilization produced by adjacent pentagon pairs (APPs) at about 19-24 kcalmol~(-1) per APP.