TmCN@C82: Monometallic Clusterfullerene Encapsulating a Tm3+ Ion

Abstract

Metal cyanide clusterfullerenes (CYCFs) are formed via the encapsulation of a single metal atom and a cyanide unit inside fullerene cages, endowing them with excellent properties in various applications. In this work, we report the synthesis, isolation, and characterizations of the first cases of thulium (Tm)-based CYCFs with the popular C82 carbon cages. The structural elucidation of the two TmCN@C82 isomers was achieved via diverse analytical techniques, including mass spectrometry, Vis-NIR spectroscopy, single-crystal X-ray crystallography, and cyclic voltammetry. The crystallographic analyses unambiguously confirmed the molecular structures of the two TmCN@C82 isomers as TmCN@Cs(6)-C82 and TmCN@C2v(9)-C82. Both TmCN clusters adopt a well-established triangular configuration, with the Tm ion located on the symmetrical plane of the carbon cages. The electronic structures of both TmCN@C82 isomers adopt a Tm3+(CN)−@(C82)2− configuration, exhibiting characteristic spectral and electrochemical properties reminiscent of divalent endohedral metallofullerenes (EMFs). Intriguingly, unlike the divalent Tm2+ ion observed in the mono-metallofullerenes Tm@C2n, a higher oxidation state of Tm3+ is identified in the monometallic TmCN cluster due to bonding with the cyanide anion. This result provides valuable insight into the essential role of the non-metallic endo-units in governing the oxidation state of the metal ion and the electronic behaviors of EMFs.