Increasing the temperature at which molecules behave as single-molecule magnets is a serious challenge in molecular magnetism. One of the ways to address this problem is to create the molecules with strongly coupled lanthanide ions. In this work, endohedral metallofullerenes Y2@C80 and Dy2@C80 are obtained in the form of air-stable benzyl monoadducts. Both feature an unpaired electron trapped between metal ions, thus forming a single-electron metal-metal bond. Giant exchange interactions between lanthanide ions and the unpaired electron result in single-molecule magnetism of Dy2@C80(CH2Ph) with a record-high 100 s blocking temperature of 18 K. All magnetic moments in Dy2@C80(CH2Ph) are parallel and couple ferromagnetically to form a single spin unit of 21 μB with a dysprosium-electron exchange constant of 32 cm−1. The barrier of the magnetization reversal of 613 K is assigned to the state in which the spin of one Dy centre is flipped.

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.

Clusterfullerenes are capable of entrapping a variety of metal clusters within carbon cage, for which the entrapped metal cluster generally keeps its geometric structure (e.g., bond distance and angle) upon changing the isomeric structure of fullerene cage, and whether the properties of the entrapped metal cluster is geometry-dependent remains unclear. Herein we report an unusual triangular monometallic cluster entrapped in fullerene cage by isolating several novel terbium cyanide clusterfullerenes (TbNC@C) with different cage isomeric structures. Upon varying the isomeric structure of C cage from C(5) to C(6) and to C(9), the entrapped triangular TbNC cluster exhibits significant distortions as evidenced by the changes of Tb-C(N) and C-N bond distances and variation of the Tb-C(N)-N(C) angle by up to 20°, revealing that the geometric structure of the entrapped triangular TbNC cluster is variable. All three TbNC@C molecules are found to be single-ion magnets, and the change of the geometric structure of TbNC cluster directly leads to the alternation of the magnetic relaxation time of the corresponding TbNC@C clusterfullerene.

Fused‐pentagons results in an increase of local steric strain according to the isolated pentagon rule (IPR), and for all reported non‐IPR clusterfullerenes multiple (two or three) metals are required to stabilize the strained fused‐pentagons, making it difficult to access the single‐atom properties. Herein, we report the syntheses and isolations of novel non‐IPR mononuclear clusterfullerenes MNC@C76 (M=Tb, Y), in which one pair of strained fused‐pentagon is stabilized by a mononuclear cluster. The molecular structures of MNC@C76 (M=Tb, Y) were determined unambiguously by single‐crystal X‐ray diffraction, featuring a non‐IPR C 2v(19138)‐C76 cage entrapping a nearly linear MNC cluster, which is remarkably different from the triangular MNC cluster within the reported analogous clusterfullerenes based on IPR‐obeying C82 cages. The TbNC@C76 molecule is found to be a field‐induced single‐molecule magnet (SMM).

A method for the selective synthesis of sulfide clusterfullerenes Dy2S@C2n is developed. Addition of methane to the reactive atmosphere reduces the formation of empty fullerenes in the arc-discharge synthesis, whereas the use of Dy2S3 as a source of metal and sulfur affords sulfide clusterfullerenes as the main fullerene products along with smaller amounts of carbide clusterfullerenes. Two isomers of Dy2S@C82 with Cs(6) and C3v(8) cage symmetry, Dy2S@C72-Cs(10528), and a carbide clusterfullerene Dy2C2@C82-Cs(6) were isolated. The molecular structure of both Dy2S@C82 isomers was elucidated by single-crystal X-ray diffraction. SQUID magnetometry demonstrates that all of these clusterfullerenes exhibit hysteresis of magnetization, with Dy2S@C82-C3v(8) being the strongest single molecule magnet in the series. DC- and AC-susceptibility measurements were used to determine magnetization relaxation times in the temperature range from 1.6 K to 70 K. Unprecedented magnetization relaxation dynamics with three consequent Orbach processes and energy barriers of 10.5, 48, and 1232 K are determined for Dy2S@C82-C3v(8). Dy2S@C82-Cs(6) exhibits faster relaxation of magnetization with two barriers of 15.2 and 523 K. Ab initio calculations were used to interpret experimental data and compare the Dy-sulfide clusterfullerenes to other Dy-clusterfullerenes. The smallest and largest barriers are ascribed to the exchange/dipolar barrier and relaxation via crystal-field states, respectively, whereas an intermediate energy barrier of 48 K in Dy2S@C82-C3v(8) is assigned to the local phonon mode, corresponding to the librational motion of the Dy2S cluster inside the carbon cage.

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 ...

Fused-pentagons results in an increase of local steric strain according to the isolated pentagon rule (IPR), and for all reported non-IPR clusterfullerenes multiple (two or three) metals are required to stabilizet he strained fused-pentagons, making it difficult to access the single-atom properties.Herein, we report the syntheses and isolations of novel non-IPR mononuclear clusterfullerenes MNC@C 76 (M = Tb,Y ), in which one pair of strained fused-pentagon is stabilized by amononuclear cluster.The molecular structures of MNC@C 76 (M = Tb,Y)were determined unambiguously by single-crystal X-ray diffraction, featuring an on-IPR C 2v (19138)-C 76 cage entrapping an early linear MNC cluster,w hichi sr emarkably different from the triangular MNC cluster within the reported analogous clusterfullerenes based on IPR-obeying C 82 cages. The TbNC@C 76 molecule is found to be afield-induced singlemolecule magnet (SMM). Fullerenesareclosedcarboncageswithhollowinteriors,andsuch unique structures bring about intriguing physical and chemical properties.[1] Most fullerenes isolated during the past three decades are based on classical carbon cages composed of hexagons and pentagons only, [1,2] forw hich the stability is generally determined by the isolated pentagon rule (IPR) proposed by Kroto in the 1980s.[3] According to IPR, fusedpentagons result in an increase of local steric strain of ac arbon cage,t hus destabilizing the fullerene. [3,4] Stabilization of the strained fused-pentagon within an on-IPR fullerene cage has been fulfilled by either endohedral or exohedral derivatization.[4] In particular,f or endohedral fullerenes which are as pecial class of fullerene with an atom, ion, or cluster entrapped in the interior of carbon cage, [5] the strong coordination of the entrapped metal ion(s) with the fused-pentagon gives rise to an intramolecular electron transfer and consequently stabilization of the non-IPR endohedral fullerene. [4][5][6] Most of the non-IPR endohedral fullerenes reported to date are based on clusterfullerenes [7] owing to the feasibility of entrapping multiple metals in diverse forms of metal clusters,s uch as Sc 3 N@C 68 , [6a,b] Gd 3 N@C 2n (2n = 78, 82, 84), [6c-e] LaSc 2 N@C 80 , [6f] and Sc 2 S@C 72 .[6g] Noteworthy,f or these reported non-IPR clusterfullerenes,multiple (two or three) metal ions are required to stabilize simultaneously the charged metal clusters and the fused-pentagons.H ence,i ti sd esirable to synthesize novel non-IPR endohedral fullerenes containing mononuclear metal clusters.Clusterfullerenes have been recently recognized as single molecule magnets (SMMs) with potential applications in spintronics,q uantum computing,a nd high-density storage devices. [8,9] To date only af ew endohedral fullerene SMMs have been reported, including Ln x Sc 3Àx N@C 80 (Ln = Dy,H o, x = 1, 2) [9a-d] and Dy 2 TiC@C 80 , [9e] which are all based on an I h -C 80 cage entrapping multiple rare-earth-metal ions that are fixed as atriangle along with the central non-magnetic ion (N or C)...

Two isomers of metallofullerene Dy2S@C82 with sulfur-bridged Dy ions exhibit broad magnetic hysteresis with sharp steps at sub-Kelvin temperature. Analysis of the level crossing events for different orientations of magnetic...