Author: ["Antonio Rodríguez-Fortea","Núria Alegret","Alan L. Balch","Josep M. Poblet"]
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Abstract
Fullerenes tend to follow the isolated pentagon rule, which requires that each of the 12 pentagons is surrounded only by hexagons. Over the past decade many violations to this rule were reported for endohedral fullerenes. Based on the ionic model M3N6+@C2n6− and the orbital energies of the isolated cages, in 2005 we formulated a molecular orbital rule to identify the most suitable hosting cages in endohedral metallofullerenes. Now, we give physical support to the orbital rule, and we propose the maximum pentagon separation rule, which can be applied to either isolated pentagon rule cages or to non-isolated pentagon rule cages with the same number of adjacent pentagon pairs. The maximum pentagon separation rule can be formulated as 'The electron transfer from the internal cluster to the fullerene host preferentially adds electrons to the pentagons; therefore, the most suitable carbon cages are those with the largest separations among the 12 pentagons'. Stable fullerenes often follow the isolated pentagon rule, but there are increasing examples of compounds that do not. Now, a maximum pentagon separation rule is proposed, which predicts that the most stable cages are those with pentagons having the largest separation. Cite this article
Rodríguez-Fortea, A., Alegret, N., Balch, A. et al. The maximum pentagon separation rule provides a guideline for the structures of endohedral metallofullerenes. Nature Chem 2, 955–961 (2010). https://doi.org/10.1038/nchem.837 