Structures of Gd 3 N@C 80 Prato Bis-Adducts: Crystal Structure, Thermal Isomerization, and Computational Study.

The structures of two bis-ethylpyrrolidinoadducts of Gd ₃ N@ I _h - C ₈₀ , obtained by regioselective 1,3-dipolar cycloadditions, were elucidated by single crystal X-ray, visible-near infrared (vis-NIR) spectra, studies on their thermal isomerization, and theoretical calculations. The structure of the minor-bis-adduct reveals a C ₂ -symmetric carbon cage with [6,6][6,6]-addition sites and with an endohedral Gd ₃ N cluster that is completely flattened. This is the first example of a crystal structure of Gd ₃ N@ I _h - C ₈₀ derivatives. The structure of the major-bis-adduct was inferred by the vis-NIR spectrum being corresponded to the structure of a previously reported major-bis-adduct of Y ₃ N@ I _h - C ₈₀ known to have an asymmetric [6,6][6,6]-structure. Based on experimental results showing that the minor-bis-adduct of Gd ₃ N@ I _h - C ₈₀ isomerized to the major-adduct, a possible second addition site was elucidated with support from density functional theory calculations.