Isolated aromatic patches as a rule to select metallofullerene multiple adducts with high chemical stabilities

Metallofullerene multiple adducts (MMAs) have properties inherited from fullerene cores and new properties from exohedral chemical groups. However, the huge structural varieties of MMAs hinder their separation, purification and characterization. Here, we report that only subsets with large first excitation energies (FEEs) are chemically stable and likely to survive experimentally. On the basis of quantum confinement effect, we propose and verify a simple rule of thumb to quickly predict whether MMAs have large FEEs: only those whose sp(2)-carbons form aromatic patches isolated by sp(3)-carbons have large FEEs. It can serve as a tool for rapid screening of MMAs with high chemical stabilities. The rule involves the concept of forming anionic aromatic patches containing metals, which further provides an explicit physical picture on the metal-cage interaction within metallofullerenes. The results present here will not only benefit the future study of MMAs but also provide insights into the fundamental chemistry of metallofullerenes. (C) 2015 Elsevier Ltd. All rights reserved.