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Sc3N@C80: computations on the two-isomer equilibrium at high temperatures
Zdenek Slanina1, Shigeru Nagase
1Department of Theoretical Molecular Science, Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Aichi, Japan. zdenek@ims.ac.jp
Summary
Computational studies reveal that the relative concentrations of Sc3N@C80 isomers depend heavily on temperature and the motion of the Sc3N molecule within the C80 cage. Including entropy is crucial for accurate population predictions.
Area of Science:
- Computational Chemistry
- Materials Science
- Nanotechnology
Background:
- Scandium nitride (Sc3N) encapsulated in fullerene cages (Sc3N@C80) exists in multiple isomers.
- Two isomers, obeying the isolated-pentagon rule with I(h) and D(5h) symmetries, are experimentally known.
Purpose of the Study:
- To computationally determine the relative concentrations of the two known Sc3N@C80 isomers.
- To investigate the influence of temperature and molecular motion on isomer populations.
Main Methods:
- Density functional theory (DFT) calculations were employed.
- Gibbs energy was computed over a broad temperature range.
- The effect of the encapsulate's motion within the fullerene cage was considered.
Main Results:
- At high temperatures (2100-2450 K), the calculated isomer populations match experimental observations (10-17% for D(5h)) when free motion is allowed.
- Neglecting the entropy term significantly underestimates the D(5h) isomer population (1% at 2100 K).
- A large interisomeric separation potential energy (19 kcal mol(-1)) highlights the importance of entropy.
Conclusions:
- The relative populations of Sc3N@C80 isomers are strongly influenced by temperature and the dynamics of the encapsulated Sc3N cluster.
- Accurate prediction of isomer distribution requires the inclusion of entropic effects in thermodynamic calculations.
- This study provides insights into the factors governing the stability and formation of fullerene-based endohedral complexes.