Nd─Nd Bond in I_h and D_5h Cage Isomers of Nd₂@C₈₀ Stabilized by Electrophilic CF₃ Addition

Abstract

Synthesis of molecular compounds with metal–metal bonds between 4f elements is recognized as one of the fascinating milestones in lanthanide metallochemistry. The main focus of such studies is on heavy lanthanides due to the interest in their magnetism, while bonding between light lanthanides remains unexplored. In this work, the Nd─Nd bonding in Nd‐dimetallofullerenes as a case study of metal–metal bonding between early lanthanides is demonstrated. Combined experimental and computational study proves that pristine Nd2@C80 has an open shell structure with a single electron occupying the Nd─Nd bonding orbital. Nd2@C80 is stabilized by a one‐electron reduction and further by the electrophilic CF3 addition to [Nd2@C80]−. Single‐crystal X‐ray diffraction reveals the formation of two Nd2@C80(CF3) isomers with D5h‐C80 and Ih‐C80 carbon cages, both featuring a single‐electron Nd─Nd bond with the length of 3.78–3.79 Å. The mutual influence of the exohedral CF3 group and endohedral metal dimer in determining the molecular structure of the adducts is analyzed. Unlike Tb or Dy analogs, which are strong single‐molecule magnets with high blocking temperature of magnetization, the slow relaxation of magnetization in Nd2@Ih‐C80(CF3) is detectable via out‐of‐phase magnetic susceptibility only below 3 K and in the presence of magnetic field.

Capturing Unstable Metallofullerenes

“…The difference from empty fullerenes is that the LUMO of dimetallofullerenes is usually a metal-metal bonding orbital, and its energy depends on the metal. For heavier lanthanides, starting with Nd, the energy of the metal-based LUMO becomes so low that the triplet state, in which one unpaired electron occupies the metal-based MO and one occupies the fullerene MO, becomes more stable than the closed-shell singlet [56,57]. (4) Clusterfullerenes, i.e., metallofullerenes with endohedral clusters such as M 3 N, M 2 C 2 , M 2 O, M 2 S, etc., usually have a closed-shell electronic structure of the carbon cage, and the vast majority of them can be obtained from the soot and separated by procedure I.…”

Covalency versus magnetic axiality in Nd molecular magnets: Nd-photoluminescence, strong ligand-field, and unprecedented nephelauxetic effect in fullerenes NdM2N@C80 (M = Sc, Lu, Y)

“…65 Nd-EMFs are among the least studied Ln-EMFs, and the first example of the SMM behavior of EMFs with light lanthanides, Nd 2 @C 80 (CF 3 ), has only recently been reported. 78 This lack of studies echoes the situation with light-lanthanide SMMs in general, which are substantially less explored than their heavy-lanthanide congeners. 79,80 Thus, despite the ubiquitous NIR luminescence known for Nd III complexes and solids, the reports on the combination of slow relaxation of magnetization and Nd-based luminescence remain scarce.…”

Fullerene rotation dictated by benzene–fullerene interactions

“…1–4 Elucidating the structures of these metallofullerenes with single-crystal X-ray diffraction proved powerful in understanding these novel molecules. 5–14 Determining the structure with high accuracy is fundamentally important to understand their properties such as bonding interactions between the entities of metallofullerenes and the crystal field around the metal ions. 15–23 The ubiquitous disorders (more than 95%) in metallofullerene crystals originate from the round shape of fullerene cages, which tend to rotate in the crystal lattice, and the shallow potential energy surface supplied by the fullerene cage to hold the encapsulated metal ions.…”

“…24,26,49–51 The recently reported M 2 @C 80 -CF 3 (M = Tb, Nd) co-crystallized with NiOEP also shows such tendency. 5,52 The Dy 2 ScN cluster shown in Fig. S6 in the ESI† reveals that the encapsulated Dy 2 ScN sits above the N–Ni–N bonds at 100 K, while exhibiting rotation at 180 and 260 K, showing the subtle interaction between metal ions and the NiOEP molecule.…”