Redox-active scandium oxide cluster inside a fullerene cage: spectroscopic, voltammetric, electron spin resonance spectroelectrochemical, and extended density functional theory study of Sc4O2@C80 and its ion radicals

Functionalized Fullerenes and Their Applications in Electrochemistry, Solar Cells, and Nanoelectronics

Carbon-based nanomaterials have rapidly advanced over the last few decades. Fullerenes, carbon nanotubes, graphene and its derivatives, graphene oxide, nanodiamonds, and carbon-based quantum dots have been developed and intensively studied. Among them, fullerenes have attracted increasing research attention due to their unique chemical and physical properties, which have great potential in a wide range of applications. In this article, we offer a comprehensive review of recent progress in the synthesis and the chemical and physical properties of fullerenes and related composites. The review begins with the introduction of various methods for the synthesis of functionalized fullerenes. A discussion then follows on their chemical and physical properties. Thereafter, various intriguing applications, such as using carbon nanotubes as nanoreactors for fullerene chemical reactions, are highlighted. Finally, this review concludes with a summary of future research, major challenges to be met, and possible solutions.

Molecular structures and magnetic properties of endohedral metallofullerenes

Endohedral metallofullerenes have fascinating core-shell structures, with metal atoms or metal clusters encaged in fullerene cages, and they display various chemical, optical and magnetic properties derived from different types of fullerene cages and metal moieties. Fullerene cages can act as carriers to stabilize unusual cluster moieties. Many bizarre species that are hard to produce via synthetic methods survive well under the protection of a fullerene cage, making metallofullerenes ideal platforms for generating new clusters and bonds. Fullerene cages can also be carriers to hold active unpaired electrons. Some metallofullerenes possess electron spin and show intriguing magnetic properties, making them applicable for use in quantum computing, high density information storage and magnetoreception systems. The exploration of new metallofullerenes is still ongoing, while function-oriented studies are also promoted for the future application of metallofullerenes. Herein, we highlight the recent progress in the synthesis, electron spin characteristics and magnetic properties of metallofullerenes. Discussions and an outlook on the future development of metallofullerenes are also stated.

Unusually large hyperfine structure of the electron spin levels in an endohedral dimetallofullerene and its spin coherent properties

We report the synthesis, ESR spectroscopic and spin coherent properties of the dimetallofullerene Sc2@C80(CH2Ph). The single-electron metal-metal bond of the Sc2 dimer inside the fullerene's cage is stabilized with the electron spin density being fully localized at the metal bond. This results in an extraordinary strong hyperfine interaction of the electron spin with the 45Sc nuclear spins with a coupling constant a = 18.2 mT (∼510 MHz) and yields a fully resolved hyperfine-split ESR spectrum comprising 64 lines. The splitting is present even at low temperatures where the molecular dynamics are completely frozen. The large extent and the robustness of the hyperfine-split spectra enable us to identify and control the well-defined transitions between specific electron-nuclear quantum states. This made it possible to demonstrate in our pulse ESR study the remarkable spin coherent dynamics of Sc2@C80(CH2Ph), such as the generation of arbitrary superpositions of the spin states in a nutation experiment and the spin dephasing times above 10 μs at temperatures T < 80 K reaching the value of 17 μs at T ≤ 20 K. These observations suggest Sc2@C80(CH2Ph) as an interesting qubit candidate and motivate further synthetic efforts to obtain fullerene-based systems with superior spin properties.

Crystallographic evidence and spin activation for the Russian-doll-type metallofullerene Sc4C2@C80

We report unambiguous crystallographic evidence for the Russian-doll-type metallofullerene Sc4C2@Ih-C80. 45Sc NMR further demonstrates the tetrahedron arrangement of the Sc4C2 cluster. Moreover, the electrochemical test reveals the stable oxidation state of Sc4C2@C80. Hence, the Sc4C2@C80 cation radical was studied by electron spin resonance spectroscopy. These results provide better understanding for the previously less-explored Sc4C2@C80.

Scandium Tetrahedron Supported by H Anion and CN Pentaanion inside Fullerene C80

Endohedral metallofullerenes have greatly expanded the range of the fullerene family due to their nesting structure and unusual encapsulated clusters protected by a fullerene cage. Herein, we report a metallofullerene Sc₄CNH@I_h-C₈₀, which has a scandium tetrahedron supported by H and CN anions inside fullerene C₈₀. Sc₄CNH@I_h-C₈₀ has a rare multilayer nesting structure, and the internal Sc₄CNH is the most complex endohedral cluster disclosed to date. Sc₄CNH@I_h-C₈₀ has so many bonding types (metal-carbide, metal-nitride, and metal-hydride), which weave a polyhedron of Sc₄CNH clusters. This work shows that the endohedral metallofullerenes have the potential to build inorganic nesting polyhedra that have distinctive architectures and unique electronic properties. Sc₄CNH@I_h-C₈₀ was synthesized by means of the arc-discharge method using scandium and graphite under the mixed atmosphere of hydrogen, nitrogen, and helium. It is the first time to disclose an unprecedented metal-hydride bond in a fullerene cage. This result shows that the endohedral fullerenes bearing hydrogen species can be synthesized by the arc-discharge technique under an atmosphere of hydrogen. This work demonstrates that a fullerene cage can be an ample carrier to encapsulate unusual cluster moieties.

Trapping Metallic Oxide Clusters inside Fullerene Cages

The sub-nanometer sized void inside a fullerene cage permits the accommodation of a single atom, atomic cluster, or even small molecule, resulting in the formation of endohedral fullerenes. Particularly, clusterfullerenes can be formed by encapsulating multiple metallic ions in most cases along with nonmetal ions (i.e., N^3-, C₂^2-, S^2-, O^2-) inside the fullerene cage. Such an association makes clusterfullerene more functional than empty fullerenes and conventional mono-metallofullerenes. To date, a variety of clusterfullerenes have been reported, including metal nitrides, carbides, oxides, sulfides, cyanides, and so on. Among them, oxide clusterfullerenes (OCFs) can contain variable oxide clusters (i.e., M₄O₂, M₄O₃, M₃O, and M₂O; M = Sc or other metal), yielding one of the most versatile families. Thus, OCFs may provide a more convenient platform for developing new functional molecules and for studying previously less-explored topics such as formation mechanisms of clusterfullerenes. In this Account, we review recent progress in the field of OCFs, including their synthesis, isolation, and structural and electrochemical studies as well as the preliminary exploration into their potential functions and applications. Thanks to the concrete crystallographic results of an OCF series, we can track the transition of endohedral cluster and fullerene cage. It is suggested that the configuration and internal dynamics of the oxide cluster are highly dependent on not only the cage size but also cage structure. On the other hand, based on the experimental observations, two competitive transformation pathways are established for the majority of OCFs, verifying the bottom-up or top-down formation mechanism. It is also found that the redox behaviors of OCFs are more or less comparable to their isoelectronic species with common cage structure and similar cluster geometry but varied greatly with the cluster variety (i.e., Sc₂O vs Sc₄O_2-3). The mechanism behind such phenomena has been discussed. In addition, the potential of Dy-based OCFs as single molecular magnets (SMMs) is presented theoretically. Nevertheless, experimental advance remains to be achieved.

When metal clusters meet carbon cages: endohedral clusterfullerenes

Fullerenes have the characteristic of a hollow interior, and this unique feature triggers intuitive inspiration to entrap atoms, ions or clusters inside the carbon cage in the form of endohedral fullerenes. In particular, upon entrapping an otherwise unstable metal cluster into a carbon cage, the so-called endohedral clusterfullerenes fulfil the mutual stabilization of the inner metal cluster and the outer fullerene cage with a specific isomeric structure which is often unstable as an empty fullerene. A variety of metal clusters have been reported to form endohedral clusterfullerenes, including metal nitrides, carbides, oxides, sulfides, cyanides and so on, making endohedral clusterfullerenes the most variable and intriguing branch of endohedral fullerenes. In this review article, we present an exhaustive review on all types of endohedral clusterfullerenes reported to date, including their discoveries, syntheses, separations, molecular structures and properties as well as their potential applications in versatile fields such as biomedicine, energy conversion, and so on. At the end, we present an outlook on the prospect of endohedral clusterfullerenes.

Sc3CH@C80: selective (13)C enrichment of the central carbon atom

Sc₃CH@C₈₀ is synthesized and characterized by ¹H, ¹³C, and ⁴⁵Sc NMR. A large negative chemical shift of the proton, −11.73 ppm in the I_h and −8.79 ppm in the D_5h C₈₀ cage isomers, is found. ¹³C satellites in the ¹H NMR spectrum enabled indirect determination of the ¹³C chemical shift for the central carbon at 173 ± 1 ppm. Intensity of the satellites allowed determination of the ¹³C content for the central carbon atom. This unique possibility is applied to analyze the cluster/cage ¹³C distribution in mechanistic studies employing either ¹³CH₄ or ¹³C powder to enrich Sc₃CH@C₈₀ with ¹³C.

Confining the spin between two metal atoms within the carbon cage: redox-active metal-metal bonds in dimetallofullerenes and their stable cation radicals

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.

Awaking N-hyperfine couplings in charged yttrium nitride endohedral fullerenes

Charged yttrium nitride endohedral fullerenes show particular N-hyperfine couplings that are sensitive to the outer carbon cage.

The Driving Force of Photoinduced Charge Separation in Metal-Cluster-Encapsulated Triphenylamine-[80]fullerenes

Understanding photoinduced charge separation in fullerene-based dye-sensitized solar cells is crucial for the development of photovoltaic devices. We investigate here how the driving force of the charge separation process in conjugates of M@C₈₀ (M=Sc₃ N, Sc₃ CH, Sc₃ NC, Sc₄ O₂ , and Sc₄ O₃ ) with triphenylamine (TPA) depends on the nature of the metal cluster. Both singlet and triplet excited-state electron-transfer reactions are considered. These results based on TD-DFT calculations demonstrate that the driving force of charge separation in TPA-M@C₈₀ can be tuned well by varying the structure of the metal cluster encapsulated inside the fullerene cage.

Synthesis and Isolation of the Titanium-Scandium Endohedral Fullerenes-Sc2 TiC@Ih -C80 , Sc2 TiC@D5h -C80 and Sc2 TiC2 @Ih -C80 : Metal Size Tuning of the Ti(IV) /Ti(III) Redox Potentials

The formation of endohedral metallofullerenes (EMFs) in an electric arc is reported for the mixed-metal Sc-Ti system utilizing methane as a reactive gas. Comparison of these results with those from the Sc/CH4 and Ti/CH4 systems as well as syntheses without methane revealed a strong mutual influence of all key components on the product distribution. Whereas a methane atmosphere alone suppresses the formation of empty cage fullerenes, the Ti/CH4 system forms mainly empty cage fullerenes. In contrast, the main fullerene products in the Sc/CH4 system are Sc4 C2 @C80 (the most abundant EMF from this synthesis), Sc3 C2 @C80 , isomers of Sc2 C2 @C82 , and the family Sc2 C2 n (2 n=74, 76, 82, 86, 90, etc.), as well as Sc3 CH@C80 . The Sc-Ti/CH4 system produces the mixed-metal Sc2 TiC@C2 n (2 n=68, 78, 80) and Sc2 TiC2 @C2 n (2 n=80) clusterfullerene families. The molecular structures of the new, transition-metal-containing endohedral fullerenes, Sc2 TiC@Ih -C80 , Sc2 TiC@D5h -C80 , and Sc2 TiC2 @Ih -C80 , were characterized by NMR spectroscopy. The structure of Sc2 TiC@Ih -C80 was also determined by single-crystal X-ray diffraction, which demonstrated the presence of a short Ti=C double bond. Both Sc2 TiC- and Sc2 TiC2 -containing clusterfullerenes have Ti-localized LUMOs. Encapsulation of the redox-active Ti ion inside the fullerene cage enables analysis of the cluster-cage strain in the endohedral fullerenes through electrochemical measurements.

Spatial aromatic fences of metal-organic frameworks for manipulating the electron spin of a fulleropyrrolidine nitroxide radical

The electron spin properties of a fulleropyrrolidine nitroxide radical incarcerated in the pores of MOF-177 and MIL-53 respectively were investigated for the first time. It was found that the spatial confinement effect and intramolecular interactions in these two solid-state spin systems lead to dramatically distinctive spin dynamics.

U@C36. Is there enough room for a second uranium?

The possible encapsulation of a second uranium in U@C₃₆ is evaluated theoretically.

Sc2O@C(2v)(5)-C80: Dimetallic Oxide Cluster Inside a C80 Fullerene Cage

A new oxide cluster fullerene, Sc2O@C(2v)(5)-C80, has been isolated and characterized by mass spectrometry, UV-vis-NIR absorption spectroscopy, cyclic voltammetry, (45)Sc NMR, DFT calculations, and single crystal X-ray diffraction. The crystallographic analysis unambiguously elucidated that the cage symmetry was assigned to C(2v)(5)-C80 and suggests that the Sc2O cluster is ordered inside the cage. The crystallographic data further reveals that the Sc1-O-Sc2 angle is much larger than that found in Sc2O@T(d)(19151)-C76 but almost comparable to that in Sc2O@Cs(6)-C82, suggesting that the endohedral Sc2O unit is flexible and can display large variation in the Sc-O-Sc angle, which depends on the size and shape of the cage. Computational studies show that there is a formal transfer of four electrons from the Sc2O unit to the C80 cage, i.e., (Sc2O)(4+)@(C80)(4-), and the HOMO and LUMO are mainly localized on the C80 framework. Moreover, thermal and entropic effects are seen to be relevant in the isomer selection. Comparative studies between the recently reported Sc2C2@C(2v)(5)-C80 and Sc2O@C(2v)(5)-C80 reveal that, despite their close structural resemblance, subtle differences exist on the crystal structures, and the clusters exert notable impact on their spectroscopic properties as well as interactions between the clusters and corresponding cages.

Sc2O@Td 19151)-C76 : hindered cluster motion inside a tetrahedral carbon cage probed by crystallographic and computational studies

A new cluster fullerene, Sc2 O@Td (19151)-C76 , has been isolated and characterized by mass spectrometry, UV/Vis/NIR absorption, (45) Sc NMR spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction. The crystallographic analysis unambiguously assigned the cage structure as Td (19151)-C76 , which is the first tetrahedral fullerene cage characterized by single-crystal X-ray diffraction. This study also demonstrated that the Sc2 O cluster has a much smaller ScOSc angle than that of Sc2 O@Cs (6)-C82 and the Sc2 O unit is fully ordered inside the Td (19151)-C76 cage. Computational studies further revealed that the cluster motion of the Sc2 O is more restrained in the Td (19151)-C76 cage than that in the Cs (6)-C82 cage. These results suggest that cage size affects not only the shapes but also the cluster motion inside fullerene cages.

Electron-spin excitation by implanting hydrogen into metallofullerene: the synthesis and spectroscopic characterization of Sc4C2H@I(h)-C80

A hydrogen-containing endohedral metallofullerene, Sc4C2H@Ih-C80, was synthesized and its paramagnetism was measured by the low-temperature EPR spectrometry with a broad EPR signal. The electron-spin excitation by implanting the H-atom would be a new method for preparation of stable paramagnetic metallofullerenes.

Scandium carbide/cyanide alloyed cluster inside fullerene cage: synthesis and structural studies of Sc3(μ3-C2)(μ3-CN)@Ih-C80

A new Sc3(C2)(CN)@Ih-C80 metallofullerene encaging a scandium carbide/cyanide alloyed cluster was prepared and investigated. Sc3(C2)(CN)@Ih-C80 was synthesized by the arc-discharging method and isolated by HPLC. Its experimental (13)C NMR spectrum with two signals clearly confirms an icosahedral C80 cage, and theoretically calculated (13)C NMR peaks agree well with the experimental results. Further, theoretical calculations disclosed that the endohedral μ3-C2 and μ3-CN moieties are situated on each side of the triangular shaped Sc3 unit to form a scandium carbide/cyanide alloyed cluster. Kohn-Sham molecular orbitals reveals the electronic structure of (Sc(3+))3(C2)(2-)(CN)(-)@C80(6-), in which two anions, μ3-C2(2-) and μ3-(CN)(-), construct and stabilize this special molecule together. The FTIR and Raman spectra of Sc3(C2)(CN)@Ih-C80 were analyzed by comparison of the experimental and calculated results to further confirm its structure and to uncover cluster-based vibrational modes.

Paramagnetic and theoretical study of Y₂@C₈₁N: an endohedral azafullerene radical

A metallofullerene radical Y2@C81N was synthesized and characterized by ESR spectroscopy and ab initio calculations. It was revealed that the molecule adopts an unique azafullerene C81N cage derived from C82-C(2v)(9), and two yttrium ions are entrapped to form the endohedral structure. The unpaired electron of Y2@C81N radical was calculated to mainly localize on the Y2 dimer, leading to large hyperfine coupling constants of 75.7 and 69.8 G for the two yttrium nuclei.

Anion radicals of isomeric [5,6] and [6,6] benzoadducts of Sc3N@C80: remarkable differences in endohedral cluster spin density and dynamics

The anion radicals of isomeric [5,6] and [6,6] Sc3N@C80 benzoadducts were studied by electron spin resonance spectroscopy, density functional theory computations, and molecular dynamics. In both compounds the rotation of the Sc3N cluster is frozen and the spin density distribution of the cluster is highly anisotropic, with hyperfine coupling constants of 9.1 and 2 × 33.3 G for the [5,6] adduct and ∼0.6 and 2 × 47.9 G for the [6,6] adduct. Remarkably, the subtle variation of the position of the exohedral group on the surface of the cage results in very pronounced changes in the spin density distribution and the dynamics of the encapsulated Sc3N cluster.

The V-shaped polar molecules encapsulated into Cs (10528)-C72: stability and nonlinear optical response

Recently, a new sulfide cluster fullerene, Sc2S@Cs (10528)-C72 containing two pairs of fused pentagons has been isolated and characterized (Chen et al., J. Am. Chem. Soc., 2012, 134, 7851). Inspired by this investigation, we propose a question: what properties will be influenced by the interaction between the encapsulated V-shaped polar molecule and C72? To answer this question, four encapsulated metallic fullerenes (EMFs) M2N@C72 (M = Sc or Y, N = S or O) along with pristine Cs-C72 (10528) were investigated by quantum chemistry methods. The results show that the Egap (3.01-3.14 eV) of M2N@C72 are significantly greater than that of pristine Cs-C72 (10528) (2.34 eV). This indicates that the stabilities of these EMFs increase by encapsulating the V-shaped polar molecule into the fullerene. Furthermore, the natural bond orbital (NBO) charge analysis indicates electron transfer from M2N to C72 cage, which plays a crucial role in enhancing first hyperpolarizability (βtot). The βtot follows the order of 1174 au (Y2O@C72) ≈ 1179 au (Sc2O@C72) > 886 au (Y2S@C72) ≈ 864 au (Sc2S@C72) > 355 au (C72). This indicates that the βtot of M2N@C72 is more remarkable than that of pristine Cs-C72 (10528) due to the induction effect of the encapsulated molecule. Compared with sulfide cluster fullerenes (Y2S@C72 and Sc2S@C72), oxide cluster fullerenes (Sc2O@C72 and Y2O@C72) show much larger βtot due to the small ionic radius and the large electronegativity of oxygen. In contrast, the metal element (scandium and yttrium) has a slight influence on the βtot. Thus, oxide cluster fullerenes are candidates to become promising nonlinear optical materials with higher performance.

Endohedral metallofullerenes based on spherical I(h)-C(80) cage: molecular structures and paramagnetic properties

Fullerenes are carbon cages assembled from fused hexagons andpentagons that have closed networks and conjugated π systems. The curve of the fullerene structure requires that the constituent carbon atoms take on a pyramidal shape and produces extra strain energy. However, the highly symmetrical geometry of the fullerene decreases the surface tension in these structures, so highly symmetrical fullerenes are usually very stable. For example, C60 with icosahedral symmetry (Ih) is the most stable fullerene molecule. However, another highly symmetrical fullerene, Ih-C80, is extremely unstable. The reason for this difference is the open-shell electronic structure of Ih-C80, which has a 4-fold degenerate HOMO occupied by only two electrons. Predictably, once the degenerate HOMO of Ih-C80 accepts six more electrons, it forms a closed-shell electronic structure similar to Ih-C60 and with comparable stability. Because the hollow structure of fullerenes can encapsulate metal atoms and those internal metals can transfer electrons to the fullerene cage, the encapsulation of metal clusters may provide an ideal technique for the stabilization of the Ih-C80 fullerenes. In this Account, we focus on the molecular structures and paramagnetic properties of spherical Ih-C80 endohedral fullerenes encaging a variety of metal moieties, such as metal atoms (Mn), metal nitride (M3N), metal carbide (MnC2), metal carbonitride (M3CN), and metal oxides (M4Om). We introduce several types of endohedral metallofullerenes such as Sc4C2@Ih-C80, which exhibits a Russian-doll-like structure, and Sc3CN@Ih-C80, which encapsulates a planar metal carbonitride cluster. In addition, we emphasize the paramagnetic properties of Ih-C80-based metallofullerenes, such as Sc3C2@Ih-C80, Y2@C79N, and M3N@Ih-C80, to show how those spin-active species can present a controllable paramagnetism. This Account highlights an inspiring molecular world within the spherical Ih-C80 cages of various metallofullerenes.

Endohedral metal or a fullerene cage based oxidation? Redox duality of nitride clusterfullerenes Ce(x)M(3-x)N@C(78-88) (x = 1, 2; M = Sc and Y) dictated by the encaged metals and the carbon cage size

Redox behavior of endohedral metallofullerenes, in particular their oxidation process, can be classified as a fullerene-based or endohedral species-based process according to the mechanism of the electron transfer. Here we report on the phenomenon of the strain-driven electrochemical behavior achieved by encapsulating the cerium-containing clusters into a series of carbon cages ranging from C78 to C88. The Ce-based mixed metal nitride clusterfullerenes CexM3-xN@C2n (x = 1, 2; M = Sc or Y; 2n = 78-88) were synthesized and characterized. The magnitude of the inherent strain caused by the limited inner space of the carbon cage for the relatively large nitride clusters can be varied by choosing different scaffold metals (Sc, Lu, or Y) to tailor the size of the encaged CexM3-xN cluster and by matching the nitride cluster with different fullerene cages in the size range from C78 to C88. The redox properties of CexM3-xN@C2n were investigated by cyclic and square wave voltammetry. The mechanism of the electrochemical oxidation of Ce-based mixed metal nitride clusterfullerenes, in particular whether the fullerene-based oxidation or the Ce(III) → Ce(IV) process is observed, is found to be dependent on the scaffold metal and the size of the fullerene cage. The endohedral oxidation of Ce(III) to Ce(IV) was observed for a number of compounds as revealed by the negative shift of their oxidation potentials with respect to the values measured for the non-Ce analogues. Experimental studies are supported by DFT calculations. We conclude that the prerequisites for the Ce-based endohedral oxidation process are suitable inherent cluster-cage strain and sufficiently high oxidation potential of the fullerene cage.

Structural and electronic studies of metal carbide clusterfullerene Sc2C2@Cs-C72

We present a metal carbide clusterfullerene Sc2C2@Cs(10528)-C72, whose structure has been baffling for many years. A motional endohedral Sc2C2 cluster, special molecule geometry and electronic structure were found in Sc2C2@Cs(10528)-C72. The paramagnetic Sc2C2@Cs-C72 anion radical was successfully prepared by a chemical reduction method and hyperfine couplings in the ESR spectrum were observed.

Spin-active metallofullerene stabilized by the core of an NC moiety

A paramagnetic Sc(3)NC@C(80) anion radical was obtained by chemical reduction. ESR spectrometry and theoretical calculations disclosed that the core NC moiety takes possession of the unpaired electron and stabilizes the paramagnetic species. It is the first time a paramagnetic metal cyanide metallofullerene has been obtained.

Electron Spin Manipulation via Encaged Cluster: Differing Anion Radicals of Y2@C82-Cs, Y2C2@C82-Cs, and Sc2C2@C82-Cs

Endohedral metallofullerene species with controllable electron spin have attracted increasing attention along with their potential application in quantum information processing. In this paper, we report the electron spin manipulation via encage cluster through comparative studies on the anion radicals of metallofullerene Y2@C82-Cs, Y2C2@C82-Cs, and Sc2C2@C82-Cs. Although these three radical species have the same parent fullerene cage, we found that the unpaired spin characteristics as well as metal-spin couplings of them can be greatly affected by endohedral clusters. Furthermore, based on theoretical calculations, it was revealed that the encaged clusters can affect the electronic population of pristine endohedral metallofullerenes and eventually manipulate the spin distribution of their corresponding anion radicals. Our findings are referential to the spin coherence in information processing due to the variable paramagnetism of these metallofullerene radicals.