Capturing the Missing Carbon Cage Isomer of C₈₄ via Mutual Stabilization of a Triangular Monometallic Cyanide Cluster

Abstract

Monometallic cyanide clusterfullerenes (CYCFs) represent a unique branch of endohedral clusterfullerenes with merely one metal atom encapsulated, offering a model system for elucidating structure–property correlation, while up to now only C82 and C76 cages have been isolated for the pristine CYCFs. C84 is one of the most abundant fullerenes and has 24 isomers obeying the isolated pentagon rule (IPR), among which 14 isomers have been already isolated, whereas the C 2v (17)-C84 isomer has lower relative energy than several isolated isomers but never been found for empty and endohedral fullerenes. Herein, four novel C84-based pristine CYCFs with variable encapsulated metals and isomeric cages, including MCN@C 2(13)-C84 (M = Y, Dy, Tb) and DyCN@C 2v (17)-C84, have been synthesized and isolated, fulfilling the first identification of the missing C 2v (17)-C84 isomer, which can be interconverted from the C 2(13)-C84 isomer through two steps of Stone–Wales transformation. The molecular structures of these four C84-based CYCFs are determined unambiguously by single-crystal X-ray diffraction. Surprisingly, although the ionic radii of Y3+, Dy3+, and Tb3+ differ slightly by only 0.01 Å, such a subtle difference leads to an obvious change in the metal–cage interactions, as inferred from the distance between the metal atom and the nearest hexagon center of the C 2(13)-C84 cage. On the other hand, upon altering the isomeric cage from DyCN@C 2(13)-C84 to DyCN@C 2v (17)-C84, the Dy–cage distance changes as well, indicating the interplay between the encapsulated DyCN cluster and the outer cage. Therefore, we demonstrate that the metal–cage interactions within CYCFs can be steered via both internal and external routes.

UCN@Cs(6)-C82: An Encapsulated Triangular UCN Cluster with Ambiguous U Oxidation State [U(III) versus U(I)]

“…Monometallic cyanide clusterfullerene (CYCF), YCN@ C s (6)-C 82 , was first reported by Yang and co-workers in 2013 . So far, a series of lanthanide based CYCFs have been synthesized, isolated, and characterized, including MCN@ C 2 v (19138)-C 76 (M = Y, Tb, and Lu), , YCN@ C s (6)-C 82 , MCN@C 84 (M = Y, Tb, Dy), and MCN@C 82 (M = Tb, Lu, and Dy). ,− One exceptional feature of the encapsulated MCN clusters is their structural flexibility, which can exist as either triangular or nearly linear geometries inside different fullerene cages. − Thus, it is intriguing to explore the possibility of entrapping an actinide cyanide cluster into a fullerene cage, which could lead to new understanding for the binding modes of cyanide with actinide ions.…”

ThC2@C82versusTh@C84: unexpected formation of triangular thorium carbide cluster inside fullerenes

“…suggests that the encapsulated mononuclear clusters are all located on the mirror planes of fullerene cages (see Figure 3). 5,11,[42][43][44][45] Previous studies of monometallic fullerenes (only one metal ion inside the cage) have found that in fullerene cages containing symmetry planes, the metal prefers to occupy a symmetric arrangement with respect to the interacting motifs, which share one of their symmetry planes with the fullerene. 34 This observation further suggests that the endohedral mononuclear cluster also prefers to share a symmetry plane with the fullerene cages.…”

A spider hanging inside a carbon cage: off-center shift and pyramidalization of Sc3N clusters inside C84and C86fullerene cages

“…[10][11][12][13] Factors such as different carbon cage isomers, the size of the carbon cage and the metal ionic radii of encapsulated clusters can all lead to changes in the cluster configuration. [14][15][16][17][18] For instance, as the size of the carbon cage decreases, M 2 C 2 clusters change from a nearly linear stretched geometry to a constrained "butterfly" structure, whereas MCN clusters change from a nearly linear shape to a triangular configuration. 13,19,20 Moreover, in non-IPR (isolated pentagon rule) carbon cages, clusters can be deformed to obtain stronger interactions with the carbon cage due to the high local strain of the heptagon or fused pentagons, thus stabilizing these carbon cages.…”