Steering the Geometry of Butterfly-Shaped Dimetal Carbide Cluster within a Carbon Cage via Trifluoromethylation of Y2C2@C82(6)

As one of the largest sub-branches of endohedral clusterfullerenes, dimetal carbide clusterfullerene (CCF) in the form of M₂C₂@C_{2 n} is quite intriguing since an alternative structure of M₂@C_{2 n+2} as conventional dimetallofullerene may exist as well. Herein, by using high-temperature trifluoromethylation followed by HPLC separation and single-crystal X-ray diffraction study, we report for the first time the unambiguous structural determination of yttrium (Y)-based CCF as its trifluoromethyl derivatives, Y₂C₂@C₈₂(6)(CF₃)₁₆. Four isomers of Y₂C₂@C₈₂(6)(CF₃)₁₆ with different addition patterns of 16 CF₃ groups are successfully isolated, and two Y atoms of the butterfly-shaped Y₂C₂ cluster are coordinated by two cage pentagons in each isomer. The butterfly geometry of Y₂C₂ cluster varies significantly in the four Y₂C₂@C₈₂(6)(CF₃)₁₆ isomers, with Y···Y distances ranging from 3.544 to 4.051 Å dependent on the relative positions of the two yttrium-coordinated pentagons on the carbon cage.