Inorganic Chemistry, Vol.59, No.13, 9416-9423, 2020
Crystallographic Characterization of Ti2C2@D-3h(5)-C-78, Ti2C2@C-3v(8)-C-82, and Ti2C2@C-s(6)-C-82: Identification of Unsupported Ti2C2 Cluster with Cage-Dependent Configurations
Fullerene cages are ideal hosts to encapsulate otherwise unstable metallic clusters to form endohedral metallofullerenes (EMFs). Herein, a novel Ti2C2 cluster with two titanium atoms bridged by a C-2-unit has been stabilized by three different fullerene cages to form Ti2C2@D-3h(5)-C-78, Ti2C2@C-3v(8)-C-82, and Ti2C2@ C-s(6)-C-82, representing the first examples of unsupported titanium carbide clusters. Crystallographic results show that the configuration of the Ti2C2 cluster changes upon cage variation. In detail, the Ti2C2 cluster adopts a butterfly shape in Ti2C2@C-3v(8)-C-82 and Ti2C2@Cs(6)-C-82 with Ti-C-2-Ti dihedral angles of 156.35 and 147.52 degrees and Ti-Ti distances of 3.633 and 3.860 A, respectively. In sharp contrast, a stretched planar geometry of Ti2C2 is observed in Ti2C2@D-3h(5)-C-78, where a Ti-C-2-Ti angle of 176.87 degrees and a long Ti-Ti distance of 5.000 A are presented. Consistently, theoretical calculations reveal that the cluster configuration is very sensitive to the cage shape which eventually determines the electronic structures of the hybrid EMF-molecules, thus adding new insights into modern coordination chemistry.