Engineering intramolecular exchange interactions between magnetic metal atoms is a ubiquitous strategy for designing molecular magnets. For lanthanides, the localized nature of 4 f electrons usually results in weak exchange coupling. Mediating magnetic interactions between lanthanide ions via radical bridges is a fruitful strategy towards stronger coupling. In this work we explore the limiting case when the role of a radical bridge is played by a single unpaired electron. We synthesize an array of air-stable Ln 2 @C 80 (CH 2 Ph) dimetallofullerenes (Ln 2 = Y 2 , Gd 2 , Tb 2 , Dy 2 , Ho 2 , Er 2 , TbY, TbGd) featuring a covalent lanthanide-lanthanide bond. The lanthanide spins are glued together by very strong exchange interactions between 4 f moments and a single electron residing on the metal–metal bonding orbital. Tb 2 @C 80 (CH 2 Ph) shows a gigantic coercivity of 8.2 Tesla at 5 K and a high 100-s blocking temperature of magnetization of 25.2 K. The Ln-Ln bonding orbital in Ln 2 @C 80 (CH 2 Ph) is redox active, enabling electrochemical tuning of the magnetism.

The use of methane as ar eactive gas dramatically increases the selectivity of the arc-discharge synthesis of M-Ticarbide clusterfullerenes (M = Y, Nd, Gd, Dy,E r, Lu). Optimization of the process parameters allows the synthesis of Dy 2 TiC@C 80 -I and its facile isolation in asingle chromatographic step.An ew type of cluster with an endohedral acetylide unit, M 2 TiC 2 @C 80 ,i sd iscovered along with the second isomer of M 2 TiC@C 80 .D y 2 TiC@C 80 -(I,II) and Dy 2 TiC 2 @C 80 -I are shown to be single-molecule magnets (SMM), but the presence of the second carbon atom in the cluster Dy 2 TiC 2 @C 80 leads to substantially poorer SMM properties.The field of endohedral metallofullerene (EMF) research was revolutionized in 1999, when it was discovered that the presence of small amounts of nitrogen gas in the arc-discharge generator afforded Sc 3 N@C 80 ,anew type of EMF with at rimetalnitride cluster inside the carbon cage.[1] Theu se of NH 3 as areactive gas instead of molecular nitrogen resulted in much higher selectivity in the synthesis of nitride clusterfullerenes as the yield of empty fullerenes in such conditions decreased dramatically.[2] Discovery of nitride clusterfullerenes triggered exhaustive studies of other clusterfullerenes, resulting in av ariety of EMF families with endohedral S, [3] O,[4] C 2 , [5] CH, [6] CN, [7] and other nonmetal units.[8]One of the advantages of the trimetallic cluster in nitride clusterfullerenes is the possibility of combining two or even three different metals within one EMF molecule.M ixedmetal nitride clusterfullerenes may exhibit new properties not present in homometallic nitride clusterfullerenes.E xamples include unusual redox behavior, [9] stabilization of unconventional carbon cages, [10] and strong variation of chemical reactivity [11] and magnetization behavior [12] depending on the number of lanthanide ions in the cluster.H owever, ad isadvantage of the mixed-metal EMFs is the increased complexity of their chromatographic separation.Whereas nitride clusterfullerenes are usually formed with Group III metals,s uch as Sc, Y, and trivalent lanthanides, [13] Yang et al. demonstrated that as ingle Ti ion can be introduced into the mixed-metal nitride cluster together with Sc or Y. [14] Due to the trivalent Ti,M 2 TiN@C 80 clusterfullerenes have unusual electronic and chemical properties. [15] Recently,i na na ttempt to obtain Ti-based nitride clusterfullerenes with Lu using NH 3 as ar eactive gas or melamine as as olid organic nitrogen source,w eh ave discovered an ew type of clusterfullerene,L u 2 TiC@C 80 , which has an endohedral m 3 -carbide ion and aT i ÀCd ouble bond.[16] Them olecule is an isostructural analogue of Lu 2 ScN@C 80 ,i nw hich the Sc-N fragment is replaced by the isoelectronic Ti = Cfragment. Unfortunately,inthe Lu/Ti/NH 3 and Lu/Ti/melamine syntheses,L u 2 TiC@C 80 is only am inor by-product;t he products are predominantly Lu 3 N@C 2n nitride clusterfullerenes,which precludes further exploration of this new type of clusterfullerenes.H ...

Lanthanide–lanthanide bonds are exceptionally rare, and dimetallofullerenes provide a unique possibility to stabilize and study these unusual bonding patterns. The presence of metal–metal bonds and consequences thereof for the electronic properties of M2@C82 (M = Sc, Er, Lu) are addressed by electrochemistry, electron paramagnetic resonance, SQUID magnetometry and other spectroscopic techniques. A simplified non-chromatographic separation procedure is developed for the isolation of Er2@C82 (Cs(6) and C3v(8) cage isomers) and Sc2@C82 (C3v(8) isomer) from fullerene mixtures. Sulfide clusterfullerenes Er2S@C82 with Cs(6) and C3v(8) fullerene cages are synthesized for the first time. The metal–metal bonding orbital of the spd hybrid character in M2@C82 is shown to be the highest occupied molecular orbital, which undergoes reversible single-electron oxidation with a metal-dependent oxidation potential. Sulfide clusterfullerenes with a fullerene-based HOMO have more positive oxidation potentials. The metal-based oxidation of Sc2@C82-C3v is confirmed by the EPR spectrum of the cation radical [Sc2@C82-C3v]+ generated by chemical oxidation in solution. The spectrum exhibits an exceptionally large a(45Sc) hyperfine coupling constant of 199.2 G, indicating a substantial 4s contribution to the metal–metal bonding orbital. The cationic salt [Er2@C82-C3v]+SbCl6− is prepared, and its magnetization behavior is compared to that of pristine Er2@C82-C3v and Er2S@C82-C3v. The formation of the single-electron Er–Er bond in the cation dramatically changes the coupling between magnetic moments of Er ions.

The chemical functionalization of fullerene single molecule magnet Tb2@C80(CH2Ph) enables the facile preparation of robust monolayers on graphene and highly oriented pyrolytic graphite from solution without impairing their magnetic properties. Monolayers of endohedral fullerene functionalized with pyrene exhibit magnetic bistability up to a temperature of 28 K. The use of pyrene terminated linker molecules opens the way to devise integration of spin carrying units encapsulated by fullerene cages on graphitic substrates, be it single‐molecule magnets or qubit candidates.

Paramagnetic and variable temperature 13C and 45Sc nuclear magnetic resonance studies are performed for nitride clusterfullerenes MSc2N@C80 with icosahedral I h(7) carbon cage, where M runs through all lanthanides forming nitride clusters.