Crystallographic Evidence for Direct Metal–Metal Bonding in a Stable Open‐Shell La₂@I_h‐C₈₀ Derivative

Abstract

Endohedral metallofullerenes (EMFs) have novel structures and properties that are closely associated with the internal metallic species.B enzyl radical additions have been previously shown to form closed-shell adducts by attaching an odd number of addends to open-shell EMFs (sucha s Sc 3 C 2 @I h -C 80 )w hereas an even number of groups are added to closed-shell EMFs (for example Sc 3 N@I h -C 80 ). Herein we report that benzyl radical addition to the closed-shell La 2 @I h -C 80 forms as table,o pen-shell monoadduct instead of the anticipated closed-shell bisadduct. Single-crystal X-ray diffraction results showt he formation of as table radical species. In this species,t he LaÀLa distance is comparable to the theoretical value of aLa ÀLa covalent bond and is shorter than reported values for other La 2 @I h -C 80 derivatives,p roviding unambiguous evidence for the formation of direct La À La bond.

Attaining record-high magnetic exchange, magnetic anisotropy and blocking barriers in dilanthanofullerenes

“…This has been adapted to stabilise Dy 2 @C 80 -I h molecule by chemically transforming it to Dy 2 @C 80 (CH 2 Ph). [72][73][74][75] (ii) by substituting one of the carbon by nitrogen atom yielding azafullerenes such as Ln 2 @C 79 N and other analogues. 49,70,[76][77][78][79] Here, we have adopted the second approach where one carbon atom is substituted by nitrogen in Gd 2 @C 60/80 isomers yielding Gd 2 @C 59/79 N molecules (See Appendix S26-28 for optimised coordinates) possessing C s symmetry (here Gd 2 @C 79 N-C S -1 is derived from Gd 2 @C 80 -D 5h and Gd 2 @C 79 N-C S -2 is derived from Gd 2 @C 80 -C 2v , see Table 1).…”

Redox-active metal–metal bonds between lanthanides in dimetallofullerenes

“…For M = Y, localization of the spin density on the Y–Y bonding MO can be confirmed by EPR spectroscopy, which revealed similar spectra in all three types of EMFs with large isotropic 89 Y hyperfine coupling constants near of 80 G (Figure 3b,c) [17•,42••,44]. Formation of the single-electron La–La bond in La 2 @C 80 (CH 2 Ph) and similar radical monoadducts of La 2 @C 80 - I h was also confirmed by EPR spectroscopy and single-crystal X-ray diffraction [45••,46].…”

“…The lack of the metal dependence is an indication of the fullerene-based oxidation in these di-EMFs, in agreement with DFT prediction for Y 2 @C 80 (CH 2 Ph). With the first oxidation potential at +0.15 V [45••], La 2 @C 80 (CH 2 Ph) is an obvious outlier exhibiting the metal-based oxidation. Thus, the metal–metal bonding MO of La 2 @C 80 (CH 2 Ph) is depopulated in the oxidation process, whereas for other metals the single-electron M–M bond is not affected.…”

“…(b) EPR spectra of the toluene solution of Y 2 @C 80 (CH 2 Ph) at room temperature and at 150 K (below the freezing point of the solvent); the isotropic RT spectrum has g-factor of 1.9733 and the a iso ( 89 Y) value of 223.8 MHz; the axial spectral pattern in frozen solution is reproduced by g ⊥ = 1.9620, g ǁ = 1.9982, a ⊥ ( 89 Y) = 208.0 MHz, a ǁ ( 89 Y) = 245.9 MHz; (c) spin density distribution in Y 2 @C 80 (CH 2 Ph) computed at the PBE0/TZVP level; (d) square wave voltammetry of M 2 @C 80 (CH 2 Ph) (M = Y, Dy, and Tb), black vertical bars denote redox potentials of La 2 @C 80 (CH 2 Ph) from Ref. [45••], dotted lines denote the first oxidation (cyan) and the first reduction (red) potentials. Based on the data from Ref.…”

Recent Progress on Endohedral Metallic Fullerenes

“…Fullerenes, a kind of zero-dimensional carbon material, are empty carbon cages consisting of fused hexagons and pentagons. [1] Metal ions [2][3][4] and clusters [5][6][7][8] can be encapsulated into the hollow cavity of fullerene cages, forming endohedral metalfullerenes (EMFs). The otherwise unstable metal ions or clusters and the carbon cage can be stabilized by the electron transfer between them.…”