Eu@C₇₂: Computed Comparable Populations of Two Non-IPR Isomers

Area of Science:

• Computational Chemistry
• Endohedral Fullerenes
• Materials Science

Background:

• Endohedral fullerenes, such as Eu@C72, are of interest due to their unique electronic and magnetic properties.
• Understanding the isomeric structures and their relative stabilities is crucial for their synthesis and application.
• The isolated-pentagon rule (IPR) is a common guideline for predicting stable fullerene structures.

Purpose of the Study:

• To computationally determine the relative concentrations of various Eu@C72 isomers.
• To investigate the influence of temperature on isomer distribution.
• To compare the stability of IPR-satisfying and non-IPR isomers.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Gibbs free energy was computed across a broad temperature range.
• Six distinct Eu@C72 isomers were analyzed, including IPR and non-IPR structures.

Main Results:

• Two non-IPR isomers, featuring a pentagon-pentagon junction, were found to be the most stable.
• These dominant non-IPR isomers exhibit comparable populations at relevant temperatures.
• The IPR-satisfying isomer is energetically and entropically disfavored.

Conclusions:

• Non-IPR structures are thermodynamically preferred for Eu@C72 under typical conditions.
• The prevalence of non-IPR isomers challenges the exclusive applicability of the isolated-pentagon rule.
• This finding has implications for the targeted synthesis and characterization of Eu@C72.