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@Ih-C80, which has a scandium tetrahedron supported by H and CN anions inside fullerene C80. Sc4CNH@Ih-C80 has a rare multilayer nesting structure, and the internal Sc4CNH is the most complex endohedral cluster disclosed to date. Sc4CNH@Ih-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@Ih-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.

Synthesis and Structural Studies of Two Paramagnetic Metallofullerenes with Isomeric C72 Cage.

We synthesized and isolated two paramagnetic metallofullerenes of La@C72 and Y@C72 with different fullerene cages, which were characterized by electron paramagnetic resonance (EPR) spectroscopy and theoretical calculations. DFT calculations disclosed two possible isomers of La/Y@C72 with C72- C2 and C72- C2v cages, both of which have similar thermodynamic stability and one pair of fused pentagons. Their paramagnetic properties were then studied by EPR spectroscopy, and the obtained EPR signals were analyzed with very different hyperfine coupling constants, revealing distinct electron spin distributions for these two species. Furthermore, the experimental coupling constants were compared with those of calculated coupling constants, and comparison results revealed that the produced La@C72 has a C72- C2v cage and Y@C72 has a C72- C2 cage. These studies illustrate that the electron spin can be used as a probe to identify metallofullerene structure due to the susceptibility of spin-metal couplings. The successful isolation and characterizations of La@C72 and Y@C72 with such a small C72 cage reveal their stability that is important for application as paramagnetic molecule materials.

Ho2O@C74: Ho2O Cluster Expands within a Small Non-IPR Fullerene Cage of C2(13333)-C74.

Steering the cluster configuration inside a fullerene cage has been one of most interesting topics in the field of fullerenes, since the physical property of a cluster fullerene may be modified accordingly. It has been well-recognized that the cluster configuration can be tuned via altering the cage size. Typically, the carbide cluster and the oxide cluster are experimentally seen to be curled up within a small fullerene cage whereas they are expanded in a large cage. In this work, a new oxide cluster fullerene Ho2O@ C2(13333)-C74 is prepared and isolated. The single-crystal X-ray diffraction (XRD) study reveals that the Ho2O cluster, however, expands within the small non-IPR cage of C2(13333)-C74 with a Ho-O-Ho angle of >170°, indicating that cluster configuration is highly related to the cage shape and cage structure as well. The DFT computation demonstrates that the cluster-to-cage electron-transfer obviously enhances the aromaticity of the motif containing the fused-pentagon pair and hence stabilizes the non-IPR cage of C2(13333)-C74. In addition, the electrochemical and magnetic properties of Ho2O@ C2(13333)-C74 are studied to further investigate the effect of endohedral Ho2O cluster.

Awaking N-hyperfine couplings in charged yttrium nitride endohedral fullerenes.

The electron spin properties of endohedral metallofullerene molecules have broad potential applications in quantum information and magnetic induction systems due to the high stability and sensitivity. Herein, we synthesized a series of Y3N@C2n (n = 40-44) molecules and studied the hyperfine structures of their anion radicals via ESR measurements and DFT calculations. N-Hyperfine couplings were clearly observed in the ESR spectra of charged Y3N@C80 and Y3N@C86 anion radicals, which are not found in the other metallofullerenes. The ESR results revealed size-dependent spin distributions and hyperfine structures, which are sensitive to subtle changes in the carbon cage and the configuration of the yttrium nitride cluster. BOMD cluster trajectories simulations indicated that the Y3N cluster almost rotates freely in neutral Y3N@C80 but there is a certain degree of limitation in the Y3N@C80 anion.

Recent advances in colour-tunable soft actuators.

In nature, some creatures have the capability to change shapes to adapt to ever-changing environments, which greatly inspire researchers to develop soft actuators. To endow soft actuators with capabilities to interact with environment and integrate more feedbacks is of great significance. Colour-tunable soft actuators that provide colour change feedbacks have therefore attracted extensive attention. Based on either chemical-colour or structural-colour based materials, a variety of colour-tunable soft actuators enabling shape deformations (or locomotion) and colour changes have been prepared and hold promise for applications in soft robotics and biomedical devices. This review summarizes the recent advances of colour-tunable soft actuators, with emphasis on their colour-change mechanisms and highlighting their applications. Existing challenges and future perspectives on colour-tunable soft actuators are presented.

Single-Molecule Magnet with Thermally Activated Delayed Fluorescence Based on a Metallofullerene Integrated by Dysprosium and Yttrium Ions.

It is vital to construct luminescent single-molecule magnets (SMMs) and explore their applications in quantum computing technique and magneto-luminescence devices. In this work, we report a luminescent single-molecule magnet with thermally activated delayed fluorescence (TADF) based on metallofullerene DyY2N@C80. DyY2N@C80 was constructed by integrating dysprosium and yttrium ions into a fullerene cage. Magnetic results suggest that DyY2N@C80 exhibits magnetic hysteresis loops below 8 K originating from the Dy3+ ion. Moreover, DyY2N@C80 exhibits TADF originating from the Y3+-coordinated carbon cage, whose luminescence peak positions and peak intensities can be obviously influenced by Dy3+. Furthermore, a supramolecular complex of DyY2N@C80 and [12]Cycloparaphenylene ([12]CPP) was then prepared to construct a single-molecule magnet with multiwavelength luminescence. The effects of host-guest interaction on photoluminescence properties of DyY2N@C80 were disclosed. Theoretical calculations were also employed to illustrate the structures of DyY2N@C80 and DyY2N@C80⊂[12]CPP.

Construction of a double-walled carbon nanoring.

The nanoring structure of cycloparaphenylenes (CPPs) can be considered as the shortest fragment of a carbon nanotube. Herein, we successfully prepared a double-walled carbon nanoring of [6]CPP⊂[12]CPP, which can be regarded as the shortest double-walled carbon nanotube. [6]CPP⊂[12]CPP was constructed through the supramolecular assembly, and its crystallographic structure was unambiguously determined by single-crystal X-ray diffraction. The host-guest interaction and charge transfer in [6]CPP⊂[12]CPP were disclosed by UV-Vis absorption, fluorescence, and electrochemical studies. Electron paramagnetic resonance (EPR) spectroscopy disclosed the stability of the [6]CPP⊂[12]CPP cation radical, whose unpaired spin was fully delocalized on the inner [6]CPP and well protected by outer [12]CPP. Moreover, [6]CPP⊂[12]CPP shows highly enhanced photoconductivity and photocurrent under light irradiation compared to those of pristine monomers. The self-assembly behavior of [6]CPP⊂[12]CPP was also studied, and it was found that [6]CPP⊂[12]CPP molecules tend to form a square rod structure in the DMF solution. Thus, these results demonstrate that this double-walled carbon nanoring material has a great potential application in photoelectronic devices and organic semiconductors.

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.

Construction of a short metallofullerene-peapod with a spin probe.

A short metallofullere-peapod of Y2@C79N⊂[4]CHBC was constructed. The strong confinement effect from the large π-extended [4]CHBC nanoring induces molecular orientation of the wrapped Y2@C79N, which can be sensed by a Y2@C79N spin probe. The low susceptibility of the spin phase memory time (Tm) for the Y2@C79N spin was also found in a confined space.

A luminescent single-molecule magnet of dimetallofullerene with cage-dependent properties.

It is important to explore luminescent single-molecule magnets (SMMs) to promote their application in high-density data storage. Herein, we report two dimetallofullerenes of DyEr@C82 isomers, which exhibit cage-dependent single-molecule magnet behavior and photoluminescence properties. DyEr@C82 isomers were characterized with a Cs and C3v cage symmetry by UV-vis-NIR spectroscopy and single-crystal X-ray diffraction analysis. Magnetic results revealed that DyEr@C3v-C82 displays SMM behavior below 3 K, whereas DyEr@Cs-C82 is a paramagnet. In addition, photoluminescence (PL) was also observed for both of these two isomers, whose peak patterns are different. Theoretical calculations revealed the presence of a one-electron-two-center Dy-Er bond in these two isomers, and different electronic structures of DyEr@Cs-C82 and DyEr@C3v-C82, which agrees well with the experimental results. These results show that dimetallofullerenes are promising magneto-luminescent materials with varied properties.

An implanted paramagnetic metallofullerene probe within a metal-organic framework.

Paramagnetic endohedral metallofullerene can be used as a molecular probe because of its sensitive electron spin characters, one of which is to sense its surroundings. Metal-organic framework (MOF) materials have significant applications in selective adsorption owing to their porous structures. Herein, we report a Sc3C2@C80 spin probe implanted in MOF-177 to detect the unusual host-guest interaction between the guest molecules of metallofullerene and the host pores of the MOF. Paramagnetic Sc3C2@C80 molecules were incorporated into the pores of MOF-177 via absorption method, and there was strong π-π interaction between oleophilic metallofullerene and aromatic framework. The electron paramagnetic resonance (EPR) signals of Sc3C2@C80 in MOF-177 exhibit anisotropic properties caused by the restricted motion of implanted Sc3C2@C80. This unusual host-guest interaction between Sc3C2@C80 and MOF-177 is gradually strengthened with decreasing temperature as revealed by the EPR signals. In addition, the gas desorption from the MOF-177 pores under subatmospheric pressure can weaken the host-guest interaction and lead to slightly enhanced Sc3C2@C80 EPR signals. Furthermore, the changes in the host-guest interaction between Sc3C2@C80 and MOF-177 at different temperatures and pressures exhibit reversibility, as shown by cycling EPR measurements. These results will inspire material design and applications of fullerene and MOF complexes.

Optically Controlled Molecular Metallofullerene Magnetism via an Azobenzene-Functionalized Metal-Organic Framework.

Molecular magnets with optically controlled property have significant applications in data storage and quantum information processing. Herein, we report the optically controlled molecular magnetism of endohedral metallofullerenes, Sc3C2@C80 and DySc2N@C80, by incarcerating them into the pores of a photoswitchable azobenzene-functionalized metal-organic framework (MOF) (AzoMOF). After ultraviolet (365 nm) irradiation, the isomerization of azobenzene groups in the AzoMOF was found to be able to modulate the spin relaxation of Sc3C2@C80 and also improve the single-molecule magnet behavior of DySc2N@C80. The photoisomerization of azobenzene side groups changes the host-guest interaction between metallofullerene and AzoMOF pores and endows them with the potential to modulate the magnetic properties with light. These findings offer an effective method to create smart molecular magnetic materials and also promote their applications in information recording, spintronics, and sensors.

Triptycene molecular rotors mounted on metallofullerene Sc3C2@C80 and their spin-rotation couplings.

Molecular machines have received considerable attention due to their various applications. Except for mechanical motion, it is essential to design advanced molecular machines with integrated functions. In this study, the triptycene rotor has been covalently linked to paramagnetic metallofullerene Sc3C2@C80 with an unpaired electron spin, resulting in a coupled system between spin flip and rotor speed. Two types of triptycene rotors were employed, one is pristine triptycene and another one has a sterically hindered methyl group. Temperature-dependent electron paramagnetic resonance (EPR) spectroscopy revealed that spin-rotor coupling can be modulated by the rotation speed of triptycene rotors, which was further illustrated by variable-temperature 1H NMR. EPR simulation revealed that the rotations of the attached triptycene rotors can greatly influence the spin relaxation and spin-metal hyperfine couplings of Sc3C2@C80, realizing remote control on neighboring electron spin states. These findings of the coupled system between the molecular rotor and spin flip would provide an approach to design advanced molecular machines with magnetic function.

A magnetoreception system constructed by a dysprosium metallofullerene and nitroxide radical.

Endohedral lanthanide metallofullerene molecules exhibit various paramagnetic properties. In this study, we present a magnetoreception probe that can detect the magnetic properties of an endohedral metallofullerene via spin-paramagnet interaction between a nitroxide radical and Dy3N@C80. A cycloaddition reaction on the outer cage of Dy3N@C80 was employed to obtain two regioisomers linked with the nitroxide radical; the resultant adduct exhibits site-dependent signal intensity in the ESR spectra. This Dy3N@C80-nitroxide radical adduct has potential applications as a molecular compass with position-sensitive magnetoreception ability.

Controlling the magnetic properties of dysprosium metallofullerene within metal-organic frameworks.

Magnetic endohedral metallofullerenes represent a new family of single-molecule magnets with a spherical form and solid framework. In this manuscript, we illustrate the controllable quantum tunneling of magnetism for metallofullerene DySc2N@C80 by means of molecule encapsulation in a porous metal-organic framework (MOF-177) with strong host-guest interactions.