Metal-Dependent Stability of Pristine and Functionalized Unconventional Dimetallofullerene M₂@I_h-C₈₀

Abstract

The unstable fullerene I h -C 80 can be stabilized greatly by encapsulation of two rare-earth metal atoms in its interior. Here we present a theoretical study on the electronic structures and stabilities of dimetallofullerene M 2 @I h -C 80 (M = Y, La, Gd, Lu). Density functional calculations demonstrate that La 2 @I h -C 80 has a closed-shell configuration, whereas Y 2 @I h -C 80 has a triplet ground state. Unlike La 2 @I h -C 80 with a high stability, Y 2 @I h -C 80 is found to be a highly reactive radical due to the unpaired electron distributed on the fullerene cage. Such characteristic properties of La 2 @I h -C 80 and Y 2 @I h -C 80 originate from the different energy levels of the metal-based molecular orbitals. Y 2 @I h -C 80 can be stabilized, however, through exterior functionalization with a CF 3 group. Interestingly, metallofullerenes Gd 2 @I h -C 80 and Lu 2 @I h -C 80 have similar frontier molecular orbitals and chemical stabilities to those of Y 2 @I h -C 80 .

Endohedral Metallofullerenes: New Structures and Unseen Phenomena

“…Shinohara and co‐workers proposed that M 2 @ I h (7)‐C 80 (M=Y, Gd, Dy, etc.) has only one unpaired electron occupying the M−M bonding MO, whereas the other electron is delocalized over the carbon cage, thus the formal oxidation state of the metal atom is +2.5 . Such molecules are commonly unstable radicals but Popov and colleagues have successfully stabilized the Dy 2 @ I h (7)‐C 80 molecule by utilizing the benzyl radical addition, and a one‐electron Dy−Dy bond was finally ascertained (Figure b) …”

Single molecule magnet with an unpaired electron trapped between two lanthanide ions inside a fullerene

“…For instance, in the La 2 @C 80 - I h , each metal ion is charged 3+ and the La–La orbital in La 2 @C 80 is the LUMO27. However, for Y or lanthanides with higher energy of the M–M bonding MO than in La 2 , computations by Shinohara and colleagues28 showed that the M 2 @C 80 - I h molecule has only one unpaired electron occupying the M–M bonding MO, the other electron being delocalized over the carbon cage. The formal oxidation state of metal atoms in M 2 @C 80 - I h molecule is thus +2.5.…”

“…The formal oxidation state of metal atoms in M 2 @C 80 - I h molecule is thus +2.5. Such molecules are unstable radicals and still remain elusive, although their existence has been demonstrated by transforming into more chemically stable forms (anions2930 or derivatives283132). A single-electron M–M bond has been also stabilized by a substitution of one carbon atom by nitrogen, giving azafullerenes M 2 @C 79 N (M=Y, Gd, Tb)3334.…”

High Blocking Temperature of Magnetization and Giant Coercivity in the Azafullerene Tb2@C79N with a Single‐Electron Terbium–Terbium Bond

“…[7] Thereason for the low stability of Ln 2 @C 80 molecules with heavy lanthanides is the low energy of the LnÀLn bonding molecular orbital (MO) in the Ln 2 dimers.W henL n 2 is encapsulated in the C 80 cage,o nly five electrons are transferred to the fullerene instead of six required to obtain stable closed-shell electronic structure of C 80 -I h . [8] Ln 2 5+ @C 80 5À can be indeed stabilized by as ingle-electron reduction in the anionic form Ln 2 5+ @C 80 6À , [9] and the stable neutral derivative Ln 2 @C 80 (CH 2 Ph) can then be obtained by as ubstitution reaction of Ln 2 @C 80 À with benzyl bromide. [4g,j] Substitution of carbon by nitrogen is another way to add a"missing" electron to C 80 5À ,a st he closed-shell C 79 N 5À azafullerene cage is isoelectronic to C 80 6À (Figure 1).…”