Abstract
Structures of many endohedral metallofullerenes (EMF) are still unknown because of their very low production yield, especially for endohedral mono-metallofullerenes below C70. In the present work, we investigated the alkaline earth metal encapsulated mono-metallofullerenes M@C66 (M=Ca, Sr, Ba) theoretically, compounds which have been detected only in mass spectra. The first-principles calculations and statistical thermodynamic analysis indicate that among the C66 isomers considered, the cage C2v(4348)-C66 should be the most likely structure for M@C66, M=Ca, Sr, Ba. These compounds may adopt another cage structure, C2(4466)-C66, at high temperatures. Both M@C2v(4384)-C66 and M@C2(4466)-C66 possess relatively large HOMO-LUMO gaps, and the former also possesses high local aromaticity. Thus it is predicted that M@C2v(4348)-C66—especially Ca@C2v(4348)-C66—could be isolable in future experiments. Moreover, simulated Vis-NIR, IR, Raman and 3C NMR spectra are provided for assisting future experimental characterizations.
Abstract
Structures of many endohedral metallofullerenes (EMF) are still unknown because of their very low production yield, especially for endohedral mono-metallofullerenes below C70. In the present work, we investigated the alkaline earth metal encapsulated mono-metallofullerenes M@C66 (M=Ca, Sr, Ba) theoretically, compounds which have been detected only in mass spectra. The first-principles calculations and statistical thermodynamic analysis indicate that among the C66 isomers considered, the cage C2v(4348)-C66 should be the most likely structure for M@C66, M=Ca, Sr, Ba. These compounds may adopt another cage structure, C2(4466)-C66, at high temperatures. Both M@C2v(4384)-C66 and M@C2(4466)-C66 possess relatively large HOMO-LUMO gaps, and the former also possesses high local aromaticity. Thus it is predicted that M@C2v(4348)-C66—especially Ca@C2v(4348)-C66—could be isolable in future experiments. Moreover, simulated Vis-NIR, IR, Raman and 3C NMR spectra are provided for assisting future experimental characterizations.