Carbide Cluster Metallofullerenes: Structure, Properties, and Possible Origin

Abstract

Endohedral metallofullerenes (EMFs) are hybrid molecules with different metallic species encapsulated inside the fullerene cages. In addition to conventional EMFs that contain only metal ions, researchers have constructed novel compounds that encapsulate metallic clusters of nitride, carbide, oxide, cyanide, and sulfide. Among these structures, carbide cluster metallofullerenes (CCMFs) are unique because their synthesis requires only graphite and the metal source. As a result the molecular structures of CCMFs are particularly difficult to characterize. Two carbon atoms are encapsulated inside the cage, but they do not participate in constructing the cage framework. Recent X-ray crystallographic studies of EMFs have allowed researchers to unambiguously identify CCMFs (MxC₂@C2n). Previously most of these structures had been described as conventional EMFs Mx@C2n+2. Most of these species are scandium-containing compounds such as Sc3C₂@Ih(7)-C₈₀ [not Sc₃@C3v(7)-C₈₂], Sc₂C₂@C2v(5)-C₈₀ [not Sc₂@C₈₂], Sc₂C₂@Cs(6)-C₈₂ [not Sc₂@Cs(10)-C₈₄], Sc₂C₂@C2v(9)-C₈₂ [not Sc₂@C2v(17)-C₈₄], Sc₂C₂@C3v(8)-C₈₂ [not Sc₂@D2d(23)-C₈₄], and Sc₂C₂@D2d(23)-C₈₄ [not Sc₂@C₈₆]. Additional examples of CCMFs include Gd₂C₂@D₃(85)-C₉₂, Sc₂C₂@C2v(6073)-C₆₈, Ti₂C₂@D3h(5)-C₇₈, M₂C₂@C3v(8)-C₈₂, M₂C₂@Cs(6)-C₈₂ (M = Y, Er, etc.), Y₂C₂@C₈₄, Y₂C₂@D₃(85)-C₉₂, Y₂C₂@D₅(450)-C₁₀₀, and Lu₃C₂@D₂(35)-C₈₈. The existence of so many CCMF species reminds us that the symbol '@' (which denotes the encapsulation status of EMFs) should be used with caution with species whose molecular structures have not been determined unambiguously. This Account presents a detailed summary of all aspects of CCMFs, including historically erroneous assignments and corrected structural characterizations, along with their intrinsic properties such as electrochemical and chemical properties. We emphasize structural issues, features that are fundamental for understanding their intrinsic properties. Finally, we discuss the formation mechanism and possible origin of cluster EMFs, not just CCMFs.

Synthesis and Photophysical Properties of a Sc3N@C80‐Corrole Electron Donor–Acceptor Conjugate

“…[12] Interestingly, in corrole-C 60 conjugates, the rate of charge separation was found to be on the order of 10 10 -10 11 s À1 , which is considered as an efficient photoinduced electron-transfer process, whereas the rate of charge recombination was slowed down by 5 orders of magnitude in nonpolar solvents. [14] EMFs are a type of fullerenes, which feature metallic clusters encapsulated in their interior. [13] It is, thus, particularly desirable to find new materials with tunable electron-acceptor properties and to replace either C 60 or C 70 as electron acceptor in electron donor-acceptor conjugates.…”

Beyond the Butterfly: Sc2C2@C2v(9)-C86, an Endohedral Fullerene Containing a Planar, Twisted Sc2C2 Unit with Remarkable Crystalline Order in an Unprecedented Carbon Cage

“…9 Endohedral fullerenes with M 2 C 2n compositions can exist as conventional endohedrals, M 2 @C 2n , or as metal carbide clusters, M 2 C 2 @C 2n-2 . 10,11 In 2001, the structure of Sc 2 C 86 was unambiguously assigned as the first metal carbide clusterfullerene (MCCF), Sc 2 C 2 @D 2d (23)-C 84 , as opposed to Sc 2 @C 86 . 12 Interestingly, in all reported cases the M 2 C 2 cluster exhibits what has been described as a butterfly shape, which is illustrated in Scheme 1.…”

The inner-induced effects of YCN in C76 on the structures and nonlinear optical properties

“…Since the first EMF La@C 82 was successfully isolated by Smalley et al in 1991 [32], numerous metallofullerenes (EMFs), as derivatives of fullerenes, have attracted wide attention as a new class of technologically relevant materials because of their unique geometrical structures and electronic properties [33][34][35][36]. The EMF family is constantly growing.…”