Nd─Nd Bond in I h and D 5h Cage Isomers of Nd 2 @C 80 Stabilized by Electrophilic CF 3 Addition.

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 Nd 2 @C 80 has an open shell structure with a single electron occupying the Nd─Nd bonding orbital. Nd 2 @C 80 is stabilized by a one-electron reduction and further by the electrophilic CF 3 addition to [Nd 2 @C 80 ] - . Single-crystal X-ray diffraction reveals the formation of two Nd 2 @C 80 (CF 3 ) isomers with D 5h -C 80 and I h -C 80 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 CF 3 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 Nd 2 @I h -C 80 (CF 3 ) is detectable via out-of-phase magnetic susceptibility only below 3 K and in the presence of magnetic field.