DySc2N@C80 Single-Molecule Magnetic Metallofullerene Encapsulated in a Single-Walled Carbon Nanotube

Advances in Liquid-Phase Assembly of Clusters into Single-Walled Carbon Nanotubes

Insight into the behaviors of molecules in confined space is highly desired for the deep understanding of the mechanism of chemical reactions in a microenvironment. Yet the direct access of molecular evolutions at atomic resolution in nanoconfinements is still challenging. Among various guests, atomically precise clusters with well-defined structures are better suited for monitoring the chemical and physical processes in nanochannels because of their visibility under electron microscopy and identical structures that ensure homogeneous interactions. Developing an efficient method for assembling clusters into a confined space is essential for advancing mechanisms of these processes. In this Perspective, we provide an overview of the assembly of clusters into single-walled carbon nanotubes (SWCNTs) in the liquid phase. We begin with the introduction of assembling methodologies, followed by a discussion of mechanisms of confined assembly in liquids. The host-guest interactions between clusters and nanotubes and the molecular reactions in nanochannels revealed by transmission electron microscopy are unveiled, and the cluster@SWCNT heterostructure-based emerging applications are highlighted. At the end, we discuss the challenges and opportunities and expound our outlook in this field.

Structures, fundamental properties, and potential applications of low-dimensional C60 polymers and other nanocarbons: a review

Since carbon (C) atom has a variety of chemical bonds via hybridization between s and p atomic orbitals, it is well known that there are robust carbon materials. In particular, discovery of C60 has been an epoch making to cultivate nanocarbon fields. Since then, nanocarbon materials such as nanotube and graphene have been reported. It is interesting to note that C60 is soluble and volatile unlike nanotube and graphene. This indicates that C60 film is easy to be produced on any kinds of substrates, which is advantage for device fabrication. In particular, electron-/photo-induced C60 polymerization finally results in formation of one-dimensional (1D) metallic peanut-shaped and 2D dumbbell-shaped semiconducting C60 polymers, respectively. This enables us to control the physicochemical properties of C60 films using electron-/photo-lithography techniques. In this review, we focused on the structures, fundamental properties, and potential applications of the low-dimensional C60 polymers and other nanocarbons such as C60 peapods, wavy-structured graphene, and penta-nanotubes with topological defects. We hope this review will provide new insights for producing new novel nanocarbon materials and inspire broad readers to cultivate new further research in carbon materials.

Two-dimensional fullerene-based monolayer materials assembled by C80 and Sc3N@C80

Construction of two-dimensional (2D) materials using fullerenes as building blocks has attracted particular attention, primarily due to their ability to integrate desired functionalities into devices. However, realization of stable 2D phases of polymerized fullerenes remains a big challenge. Here, we propose two stable 2D monolayer phases with covalently bridged C80 cages, namely α-C80-2D and β-C80-2D, which are semiconductors with strong absorption in the long wave range and appreciable carrier mobility, respectively. The high stability originates from the bond energy released by the [2+2] cycloaddition polymerization of C80 is greater than the deformation energy of a cage. Starting from α-C80-2D, endohedral incorporation of the Sc3N molecule into each C80 cage leads to 2D semiconductors of α-Sc3N@C80-2D and α'-Sc3N@C80-2D, which possess exceptional stability and diverse physical properties, including unique electronic band structures, strong optical absorption in the visible (VIS) to near-infrared (NIR) regime, and anisotropic optical characteristics. Remarkably, a temperature-induced order-disorder transition in the α-Sc3N@C80-2D phase has been observed at elevated temperatures above 600 K. These findings expand the family of 2D carbon materials and provide useful clue for the potential applications of fullerene-assembled monolayer networks.

Endohedral metallofullerene molecular nanomagnets

Magnetic lanthanide (Ln) metal complexes exhibiting magnetic bistability can behave as molecular nanomagnets, also known as single-molecule magnets (SMMs), suitable for storing magnetic information at the molecular level, thus attracting extensive interest in the quest for high-density information storage and quantum information technologies. Upon encapsulating Ln ion(s) into fullerene cages, endohedral metallofullerenes (EMFs) have been proven as a promising and versatile platform to realize chemically robust SMMs, in which the magnetic properties are able to be readily tailored by altering the configurations of the encapsulated species and the host cages. In this review, we present critical discussions on the molecular structures and magnetic characterizations of EMF-SMMs, with the focus on their peculiar molecular and electronic structures and on the intriguing molecular magnetism arising from such structural uniqueness. In this context, different families of magnetic EMFs are summarized, including mononuclear EMF-SMMs wherein single-ion anisotropy is decisive, dinuclear clusterfullerenes whose magnetism is governed by intramolecular magnetic interaction, and radical-bridged dimetallic EMFs with high-spin ground states that arise from the strong ferromagnetic coupling. We then discuss how molecular assemblies of SMMs can be constructed, in a way that the original SMM behavior is either retained or altered in a controlled manner, thanks to the chemical robustness of EMFs. Finally, on the basis of understanding the structure-magnetic property correlation, we propose design strategies for high-performance EMF-SMMs by engineering ligand fields, electronic structures, magnetic interactions, and molecular vibrations that can couple to the spin states.

Building Molecular Nanomagnets by Encapsulating Lanthanide Ions in Boron Nitride Nanotubes: Ab Initio Investigation

Lanthanide-based single-ion magnets have attracted much interest due to their great potential for information storage at the level of one molecule. Among various strategies to enhance magnetization blocking in such complexes, the synthesis of axially symmetric compounds is regarded as the most promising. Here, we investigate theoretically the magnetization blocking of several lanthanide ions (Tb3+, Dy3+, Ho3+, Er3+, and Tm3+) encapsulated in highly symmetric zigzag boron nitride nanotubes (BNNTs) of different diameters with ab initio methodology. We found that Tb3+@(7,0)BNNT, Dy3+@(7,0)BNNT, and Tm3+@(5,0)BNNT are suitable SIM candidates, while the other investigated complexes from this series show no signs of magnetization blocking owing to a hard competition between contributions to the crystal field of the lanthanide ion from neighboring and more distant atoms of the nanotube.

Sorting of Cluster-Confined Metallic Single-Walled Carbon Nanotubes for Fabricating Atomically Vacant Uranium Oxide

Single-walled carbon nanotube (SWCNT) heterostructures have shown great potential in catalysis, magnetism, and nanofluidics, in which host SWCNTs with certain conductivity (metallic or semiconducting) are highly required. Herein, inspired by the large molecular weight and redox properties of polyoxometalate (POM) clusters, we reported the selective separation of POM encapsulated metallic SWCNTs (POM@m-SWCNTs) with a uniform diameter through density gradient ultracentrifugation (DGU). The confined POMs increased the SWCNT density and amplified the nanotubes' density difference, thus greatly lowering the centrifugal force (70,000g) of DGU. With this strategy, a series of POM@m-SWCNTs of ∼1.2 nm with high purity were sorted. The mechanism supported by theoretical and experimental evidence showed that the separation of m-SWCNTs depended on not only nanotube/cluster size but also the conductivity of SWCNTs. The smallest 1.2 nm m-SWCNT that can exactly accommodate a 0.9 nm-{Mo6} cluster exhibited the maximum electron transfer to inner clusters; thus, intertube π-π stacking of such m-SWCNTs was greatly loosened, leading to the preferential dispersion into individual ones and partitioning in the uppermost layer after DGU. As a proof-of-concept application, this sorting strategy was extended to separate heavy-element 238U-encapsulated m-SWCNTs. The phase-pure, tiny (1-2.5 nm) U4O9 crystals with atomic vacancy clusters were fabricated on m-SWCNTs through growth kinetic control. This work may provide a general way to construct desired actinide materials on specific SWCNTs.

Single-ion magnet behavior of Ln3+ encapsulated in carbon nanotubes: an ab initio insight

Single-molecule magnets (SMMs) have attracted large interest owing to their capability to store information at the level of a single molecule, which has great potential for applications in information technology. The key characteristic required for SMM performance is the magnetization blocking barrier, and in the last decade, impressive efforts have been made to increase its height. Herein, we report an ab initio investigation of the SMM behavior of a series of lanthanide ions (Tb3+, Dy3+, Ho3+, Er3+, Tm3+ and Yb3+) encapsulated in zigzag carbon nanotubes (CNTs) of different diameters. The results show that despite the high symmetry of the Ln environment, none of the investigated systems, except for Er3+ encapsulated in the (7,0) CNT, exhibited any blocking behavior. This is mainly attributed to the strong competition between axial and equatorial contributions to the crystal field of these encapsulated ions, resulting in weak or lack of magnetic axiality. The presented results provide useful theoretical guidance for the design of high-performance SMMs via modulating the crystal field of the ligand environment.

Lanthanide-radical single-molecule magnets: current status and future challenges

In the field of molecular magnetism, the lanthanide-radical (Ln-Rad) method has become one of the most appealing tactics for introducing strong magnetic interactions and has spurred on the booming development of heterospin single-molecule magnets (SMMs). The article is a timely retrospect on the research progress of Ln-Rad heterospin systems and special attention is invested on low dimensional Ln-Rad compounds with SMM behavior, primarily concerning with nitrogen-based radicals, semiquinone and nitroxide radicals. Rational design, molecular structures, magnetic behaviors and magneto-structural correlations are highlighted. Meanwhile, particular attention is focused on the influence of exchange couplings on the dynamic magnetic properties, with the purpose of helping to guide the design of prospective radical-based Ln-SMMs.

Comparison between DySc2N@C80 and Dy2ScN@C80 single-molecule magnetic metallofullerenes encapsulated in single-wall carbon nanotubes

Encapsulation of a metallofullerene single-molecule magnet, Dy₂ScN@C₈₀, into single-wall carbon nanotubes (SWCNTs) accelerates magnetic relaxation processes. In contrast, encapsulation of DySc₂N@C₈₀ suppresses them. The effects of the encapsulation are discussed in terms of intermolecular magnetic interactions and charge transfer among metallofullerenes and SWCNTs.

A Metallofullertube of Ce2 @C100 with a Carbon Nanotube Segment: Synthesis, Single-Molecule Conductance and Supramolecular Assembly

Tubular fullerenes can be considered as end-capped carbon nanotubes with accurate structure, which are promising nanocarbon materials for advanced single-molecule electronic devices. Herein, we report the synthesis and characterization of a metallofullertube Ce₂ @D₅ (450)-C₁₀₀ , which has a tubular C₁₀₀ cage with a carbon nanotube segment and two fullerene end-caps. As there are structure correlations between tubular Ce₂ @D₅ (450)-C₁₀₀ and spherical Ce₂ @I_h -C₈₀ , their structure-property relationship has been compared by means of experimental and theoretical methods. Notably, single-molecule conductance measurement determined that the conductivity of Ce₂ @D₅ (450)-C₁₀₀ was up to eight times larger than that of Ce₂ @I_h -C₈₀ . Furthermore, supramolecular assembly of Ce₂ @D₅ (450)-C₁₀₀ and a [12]CPP nanohoop was investigated, and theoretical calculations revealed that metallofullertube Ce₂ @D₅ (450)-C₁₀₀ adopted a "standing" configuration in the cavity of [12]CPP. These results demonstrate the special nature of this kind of metallofullertube.

Magnetic nanoribbons with embedded cobalt grown inside single-walled carbon nanotubes

Molecular magnetism and specifically magnetic molecules have recently gained plenty of attention as key elements for quantum technologies, information processing, and spintronics. Transition to the nanoscale and implementation of ordered structures with defined parameters is crucial for advanced applications. Single-walled carbon nanotubes (SWCNTs) provide natural one-dimensional confinement that can be implemented for encapsulation, nanosynthesis, and polymerization of molecules into nanoribbons. Recently, the formation of atomically precise graphene nanoribbons inside SWCNTs has been reported. However, there have been only a limited amount of approaches to form ordered magnetic structures inside the nanotube channels and the creation of magnetic nanoribbons is still lacking. In this work we synthesize and reveal the properties of cobalt-phthalocyanine based nanoribbons (CoPcNRs) encapsulated in SWCNTs. Raman spectroscopy, transmission electron microscopy, absorption spectroscopy, and density functional theory calculations allowed us to confirm the encapsulation and to reveal the specific fingerprints of CoPcNRs. The magnetic properties were studied by transverse magnetooptical Kerr effect measurements, which indicated a strong difference in comparison with the pristine unfilled SWCNTs due to the impact of Co incorporated atoms. We anticipate that this approach of polymerization of encapsulated magnetic molecules inside SWCNTs will result in a diverse class of protected low-dimensional ordered magnetic materials for various applications.

Salen-type mononuclear dysprosium complex displays significant performance of single-molecule magnet

Three salen-type mononuclear lanthanide complexes with general formula [Ln(5-NO2salcy)(NO3)(CH3OH)2] (Ln = Dy (1), Ho (2) and Er (3)) have been designed and synthesized by reactions of N,N'-bis(5-nitrosalicylaldehyde)ethane-1,2-cyclohexanediamine (5-NO2salcyH2) with various...

Rare-earth based tetrapyrrolic sandwiches: chemistry, materials and applications

This review summarises advances in chemistry of tetrapyrrole sandwiches with rare earth elements and highlights the current state of their use in single-molecule magnetism, organic field-effect transistors, conducting materials and nonlinear optics.

The first exploration of coordination chemistry using a methyl substituted o-vanillin based ligand: an example starting with Dy4/Zn2Dy2 systems displaying slow relaxation of magnetization

Two butterfly-shaped Dy4 and Zn2Dy2 complexes displaying slow relaxation of magnetization have been synthesized from a new methyl substituted o-vanillin based ligand, enlarging the scope for finding better SMMs.

Attaining record-high magnetic exchange, magnetic anisotropy and blocking barriers in dilanthanofullerenes

While the blocking barrier (U eff) and blocking temperature (T B) for "Dysprocenium" SIMs have been increased beyond liquid N2 temperature, device fabrication of these molecules remains a challenge as low-coordinate Ln3+ complexes are very unstable. Encapsulating the lanthanide ion inside a cage such as a fullerene (called endohedral metallofullerene or EMF) opens up a new avenue leading to several Ln@EMF SMMs. The ab initio CASSCF calculations play a pivotal role in identifying target metal ions and suitable cages in this area. Encouraged by our earlier prediction on Ln2@C79N, which was verified by experiments, here we have undertaken a search to enhance the exchange coupling in this class of molecules beyond the highest reported value. Using DFT and ab initio calculations, we have studied a series of Gd2@C2n (30 ≤ 2n ≤ 80), where an antiferromagnetic J Gd⋯Gd of -43 cm-1 was found for a stable Gd2@C38-D 3h cage. This extremely large and exceptionally rare 4f⋯4f interaction results from a direct overlap of 4f orbitals due to the confinement effect. In larger cages such as Gd2@C60 and Gd2@C80, the formation of two centre-one-electron (2c-1e-) Gd-Gd bonds is perceived. This results in a radical formation in the fullerene cage leading to its instability. To avoid this, we have studied heterofullerenes where one of the carbon atoms is replaced by a nitrogen atom. Specifically, we have studied Ln2@C59N and Ln2@C79N, where strong delocalisation of the electron yields a mixed valence-like behaviour. This suggests a double-exchange (B) is operational, and CASSCF calculations yield a B value of 434.8 cm-1 and resultant J Gd-rad of 869.5 cm-1 for the Gd2@C59N complex. These parameters are found to be two times larger than the world-record J reported for Gd2@C79N. Further ab initio calculations reveal an unprecedented U cal of 1183 and 1501 cm-1 for Dy2@C59N and Tb2@C59N, respectively. Thus, this study offers strong exchange coupling as criteria for new generation SMMs as the existing idea of enhancing the blocking barrier via crystal field modulation has reached its saturation point.

In silico strategy to boost stability, axiality, and barrier heights in dysprocenium SIMs via SWCNT encapsulation

Detailed ab initio CASSCF calculations coupled with periodic DFT studies on a series of [Dy(Cp)₂]⁺ molecules encapsulated in a single-wall carbon nanotube found that encapsulation offers stability to these fragile molecules and also significantly enhances the U_eff values. Most importantly, this encapsulation suppresses the key vibrations responsible for reducing the blocking temperature, offering a hitherto unknown strategy for a new generation of SIM-based devices.

Applications of Filled Single-Walled Carbon Nanotubes: Progress, Challenges, and Perspectives

Single-walled carbon nanotubes (SWCNTs), which possess electrical and thermal conductivity, mechanical strength, and flexibility, and are ultra-light weight, are an outstanding material for applications in nanoelectronics, photovoltaics, thermoelectric power generation, light emission, electrochemical energy storage, catalysis, sensors, spintronics, magnetic recording, and biomedicine. Applications of SWCNTs require nanotube samples with precisely controlled and customized electronic properties. The filling of SWCNTs is a promising approach in the fine-tuning of their electronic properties because a large variety of substances with appropriate physical and chemical properties can be introduced inside SWCNTs. The encapsulation of electron donor or acceptor substances inside SWCNTs opens the way for the Fermi-level engineering of SWCNTs for specific applications. This paper reviews the recent progress in applications of filled SWCNTs and highlights challenges that exist in the field.

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.

Dynamics and magnetic properties of NO molecules encapsulated in open-cage fullerene derivatives evidenced by low temperature heat capacity

Low-temperature heat capacity analyses for an NO-encapsulated fullerene derivative revealed (i) low-energy motion and (ii) strong magnetic anisotropy of the NO molecule due to its orbital angular momentum. The low-energy motion was attributed to reorientational motions of the NO molecules, in which only a small number (n ∼ 0.04) of NO molecules were found to participate. The NO molecules were confirmed to be paramagnetic even at 1 K. Ab-initio calculation indicated that the magnetic properties of the NO unit strongly depended on its surroundings, allowing the conformation of the fullerene cage to be estimated.

Leveraging Surface Siloxide Electronics to Enhance the Relaxation Properties of a Single-Molecule Magnet

Single-molecule magnets (SMMs) hold promise for unmatched information storage density as well as for applications in quantum computing and spintronics. To date, the most successful SMMs have been organometallic lanthanide complexes. However, their surface immobilization, one of the requirements for device fabrication and commercial application, remains challenging due to the sensitivity of the magnetic properties to small changes in the electronic structure of the parent SMM. Thus, finding controlled approaches to SMM surface deposition is a timely challenge. In this contribution we apply the concept of isolobality to identify siloxides present at the surface of partially dehydroxylated silica as a suitable replacement for archetypal ligand architectures in organometallic SMMs. We demonstrate theoretically and experimentally that isolated siloxide anchoring sites not only enable successful immobilization but also lead to a 2 orders of magnitude increase in magnetization relaxation times.

Magnetic Hysteresis at 10 K in Single Molecule Magnet Self-Assembled on Gold

Tremendous progress in the development of single molecule magnets (SMMs) raises the question of their device integration. On this route, understanding the properties of low-dimensional assemblies of SMMs, in particular in contact with electrodes, is a necessary but difficult step. Here, it is shown that fullerene SMM self-assembled on metal substrate from solution retains magnetic hysteresis up to 10 K. Fullerene-SMM DySc2N@C80 and Dy2ScN@C80 are derivatized to introduce a thioacetate group, which is used to graft SMMs on gold. Magnetic properties of grafted SMMs are studied by X-ray magnetic circular dichroism and compared to the films of nonderivatized fullerenes prepared by sublimation. In self-assembled films, the magnetic moments of the Dy ions are preferentially aligned parallel to the surface, which is different from the disordered orientation of endohedral clusters in nonfunctionalized fullerenes. Whereas chemical derivatization reduces the blocking temperature of magnetization and narrows the hysteresis of Dy2ScN@C80, for DySc2N@C80 equally broad hysteresis is observed as in the fullerene multilayer. Magnetic bistability in the DySc2N@C80 grafted on gold is sustained up to 10 K. This study demonstrates that self-assembly of fullerene-SMM derivatives offers a facile solution-based procedure for the preparation of functional magnetic sub-monolayers with excellent SMM performance.

Strong Equatorial Crystal Field Enhances the Axial Anisotropy and Energy Barrier for Spin Reversal Process in Yb2 Single Molecule Magnets

The importance of equatorial crystal fields on magnetic anisotropy of ytterbium single molecule magnets (SMMs) is observed for the first time. Herein, we report three similar dinuclear ytterbium complexes with the formula [Yb₂ (3-OMe-L)₂ (DMF)₂ (NO₃ )₂ ]⋅DMF (1), [Yb₂ (3-H-L)₂ (DMF)₂ (NO₃ )₂ ]⋅DMF⋅H₂ O (2), and [Yb₂ (3-NO₃ -L)₂ (DMF)₂ (NO₃ )₂ ] (3), [where 3-X-H₂ L=N'-(2-hydroxy-3-X-benzylidene)picolinohydrazide, X=OMe (1), H (2) NO₂ (3)]. Detailed magnetic measurements reveal the presence of weak antiferromagnetic interactions between the Yb centers and a field-induced slow relaxation of magnetization in all complexes. A higher energy barrier for spin reversal was observed for complex 1 (U_eff =50 K) and it decreases in the order of 2 (47 K) to 3 (40 K). Notably, complex 1 shows a remarkable energy barrier within the frequency range of 1-850 Hz reported for Yb-based SMMs. Further, ab initio calculations show a higher axial anisotropy and lower quantum tunneling of magnetization (QTM) in the ground state for 1 compared to 2 and 3. It was also observed that the presence of a strong crystal field in the equatorial plane (when the ∡ O1-Yb-O3 bond angle is close to 90°) enhances the axial anisotropy and improves the SMM behavior in the studied complexes. Both the experimental and theoretical analysis of relaxation dynamics discloses that Raman and QTM play major role on slow relaxation process for all complexes. To provide more insight into the exchange interactions, broken-symmetry DFT calculations were performed.

The anisotropy of the internal magnetic field on the central ion is capable of imposing great impact on the quantum tunneling of magnetization of Kramers single-ion magnets

In this work, a theoretical method, taking into account the anisotropy of the internal magnetic field (B[combining right harpoon above]int), is proposed to predict the rate of quantum tunneling of magnetization (QTM), i.e., τQTM-1, for Kramers single-ion magnets (SIMs). Direct comparison to both experimental and previous theoretical results of three typical Kramers SIMs indicates the necessity of the inclusion of the anisotropy of B[combining right harpoon above]int for accurate description of QTM. The predictions of the method here are consistent with the theory proposed by Prokof'ev and Stamp (PS). For Kramers SIMs of high magnetic axiality, the QTM rates, predicted by the method here, are almost linearly proportional to the results by the PS method. The dependence of τQTM-1 on various parameters is analyzed for model systems. The averaged magnitude of B[combining right harpoon above]int (Bave) and principal g value of the axial direction (gZ) are the parameters on which τQTM-1 is linearly dependent. The ones on which τQTM-1 is quadratically dependent are gXY, i.e., the principal g value of the transversal direction, and xaniso characterizing the anisotropy of B[combining right harpoon above]int. Compared to Bave and gZ, gXY and xaniso provide a higher order of dependence for QTM. Therefore regulation of the SMM property via introduction of desired values of gXY and xaniso ought to be a strategy more efficient than the one via Bave and gZ. Being different from the one via gXY, the strategy via xaniso to regulate the QTM has been rarely touched upon according to our best knowledge. However, this strategy could also lead to significant improvement since it is the same as gXY in the aspect of the dependence of τQTM-1.

Single molecule electronic devices with carbon-based materials: status and opportunity

The field of single molecule electronics has progressed remarkably in the past decades by allowing for more versatile molecular functions and improving device fabrication techniques. In particular, electrodes made from carbon-based materials such as graphene and carbon nanotubes (CNTs) may enable parallel fabrication of multiple single molecule devices. In this perspective, we review the recent progress in the field of single molecule electronics, with a focus on devices that utilizes carbon-based electrodes. The paper is structured in three main sections: (i) controlling the molecule/graphene electrode interface using covalent and non-covalent approaches, (ii) using CNTs as electrodes for fabricating single molecule devices, and (iii) a discussion of possible future directions employing new or emerging 2D materials.

Manipulation of Molecular Spin State on Surfaces Studied by Scanning Tunneling Microscopy

The adsorbed magnetic molecules with tunable spin states have drawn wide attention for their immense potential in the emerging fields of molecular spintronics and quantum computing. One of the key issues toward their application is the efficient controlling of their spin state. This review briefly summarizes the recent progress in the field of molecular spin state manipulation on surfaces. We focus on the molecular spins originated from the unpaired electrons of which the Kondo effect and spin excitation can be detected by scanning tunneling microscopy and spectroscopy (STM and STS). Studies of the molecular spin-carriers in three categories are overviewed, i.e., the ones solely composed of main group elements, the ones comprising 3d-metals, and the ones comprising 4f-metals. Several frequently used strategies for tuning molecular spin state are exemplified, including chemical reactions, reversible atomic/molecular chemisorption, and STM-tip manipulations. The summary of the successful case studies of molecular spin state manipulation may not only facilitate the fundamental understanding of molecular magnetism and spintronics but also inspire the design of the molecule-based spintronic devices and materials.

Cocrystals of Li+ encapsulated fullerenes and Tb(iii) double-decker single molecule magnet in a quasi-kagome lattice

Cocrystallization of a lithium ion encapsulated fullerene Li⁺@C₆₀ with a terbium(iii) phthalocyaninato porphyrinato double-decker single-molecule magnet [Tb(Pc)(OEP)] is reported. The cocrystal, containing PF₆^- as a counter anion, packs in a quasi-kagome lattice, which leads to intermolecular ferromagnetic interactions as well as the modulation of the single-molecule magnet (SMM) properties.

All-Inorganic Single-Ion Magnets in Ceramic Matrices

All-inorganic single-ion magnets representing paramagnetic ions incorporated in a crystalline diamagnetic matrix are reviewed. Key results and advantages of this approach in comparison with the common strategy based on molecular metal-organic complexes are considered, and some unsolved problems and future perspectives are discussed.

Discovery of a Fullerene-Polyoxometalate Hybrid Exhibiting Enhanced Photocurrent Response

A new C₆₀-polyoxometalate compound was synthesized by a C₆₀ derivative with a {SiW₁₁Mn} cluster connecting through a coordination bond and characterized. The photocurrent response test showed great improvement of this new compound compared to C₆₀ and the polyoxometalate precursor, which could be used as a potential photoelectric material.

General Growth of Carbon Nanotubes for Cerium Redox Reactions in High-Efficiency Redox Flow Batteries

Carbon nanotubes (CNTs) possess remarkable mechanical, electrical, thermal, and optical properties that predestine them for numerous potential applications. The conventional chemical vapor deposition (CVD) route for the production of CNTs, however, suffers from costly and complex issues. Herein, we demonstrate a general and high-yield strategy to grow nitrogen-doped CNTs (NCNTs) on three-dimensional (3D) graphite felt (GF) substrates, through a direct thermal pyrolysis process simply using a common tube furnace, instead of the costly and complex CVD method. Specifically, the NCNTs-decorated GF (NCNT-GF) electrode possesses enhanced electrocatalytic performance towards cerium redox reactions, mainly due to the catalytic effect of N atoms doped into NCNTs, and ingenious and hierarchical 3D architecture of the NCNT-GF. As a result, the cell with the NCNT-GF serving as a positive electrode shows the improved energy efficiency with increases of about 53.4% and 43.8% over the pristine GF and the acidly treated GF at a high charge/discharge rate of 30 mA cm⁻², respectively. Moreover, the as-prepared NCNT catalyst-enhanced electrode is found to be highly robust and should enable a long-term cycle without detectable efficiency loss after 500 cycles. The viable synthetic strategy reported in this study will contribute to the further development of more active heteroatom-doped CNTs for redox flow batteries.

Investigation of the role of terminal ligands in magnetic relaxation in a series of dinuclear dysprosium complexes

Three dinuclear dysprosium complexes have been studied to establish the role of terminal ligands in the magnetic properties of the complexes.

Functional Metallofullerene Materials and Their Applications in Nanomedicine, Magnetics, and Electronics

Endohedral metallofullerenes exhibit combined properties from carbon cages as well as internal metal moieties and have great potential in a wide range of applications as molecule materials. Along with the breakthrough of mass production of metallofullerenes, their applied research has been greatly developed with more and more new functions and practical applications. For gadolinium metallofullerenes, their water-soluble derivatives have been demonstrated with antitumor activity and unprecedented tumor vascular-targeting therapy. Metallofullerene water-soluble derivatives also can be applied to treat reactive oxygen species (ROS)-induced diseases due to their high antioxidative activity. For magnetic metallofullerenes, the internal electron spin and metal species bring about spin sensitivity, molecular magnets, and spin quantum qubits, which have many promising applications. Metallofullerenes are significant candidates for fabricating useful electronic devices because of their various electronic structures. This Review provides a summary of the metallofullerene studies reported recently, in the fields of tumor inhibition, tumor vascular-targeting therapies, antioxidative activity, spin probes, single-molecule magnets, spin qubits, and electronic devices. This is not an exhaustive summary and there are many other important study results regarding metallofullerenes. All of this research has revealed the irreplaceable role of metallofullerene materials.

Turning On the Near-Infrared Photoluminescence of Erbium Metallofullerenes by Covalent Modification

The photoluminescence of lanthanide ions inside fullerenes is usually very weak due to the quenching effect of the fullerene cage. In the case of Er@C₈₂, the near-infrared emission from the Er³⁺ ion is completely quenched by the C₈₂ fullerene cage. It remains challenging to turn on the photoluminescence of Er@C₈₂ and other monometallofullerenes. In this work, we adopt a covalent modification strategy to alter the electronic structure of the fullerene cage for sensitizing the near-infrared emission of Er³⁺ ions in metallofullerenes Er@C_2n (2n = 72, 76, and 82). After covalent modification with trifluoromethyl, phenyl, or dichlorophenyl groups, the erbium metallofullerenes exhibit photoluminescence at 1.5 μm, which is the characteristic emission of the Er³⁺ ion. Particularly, the otherwise nonfluorescent metallofullerene Er@C₈₂ is transformed into fluorescent derivatives by using this strategy. The photoluminescence from the Er³⁺ ion is ascribed to energy transfer from the fullerene cage to the Er³⁺ ion. According to theoretical calculations, the sensitization of the Er³⁺ ion by the fullerene cage is associated with the large HOMO-LUMO gap and the closed-shell electronic structure of the metallofullerene derivatives. This work provides useful guidance for the design and synthesis of new fluorescent metallofullerenes.

The pharmaceutical multi-activity of metallofullerenol invigorates cancer therapy

Currently, cancer continues to afflict humanity. The direct destruction and killing of tumor cells by surgery, radiation and chemotherapy gives rise to many side effects and compromised efficacy. Encouragingly, the rapid development of nanotechnology offers attractive opportunities to revolutionize the current situation of cancer therapy. Metallofullerenol Gd@C82(OH)22, in contrast to chemotherapeutics that directly kill tumor cells, demonstrates anti-tumor behavior with high efficiency and low toxicity by modulating the tumor microenvironment. Furthermore, Gd@C82(OH)22 has been recently reported to specifically target cancer stem cells. In this review, we give a concise introduction to the development of the fullerene family and then report the anti-tumor activity of Gd@C82(OH)22 based on its unique physicochemical characteristics, followed by a comprehensive summary of the anti-tumor biological mechanisms which target different components of the tumor microenvironment as well as the biodistribution and toxicity of Gd@C82(OH)22. Finally, we describe Gd@C82(OH)22 as a "particulate medicine" to highlight its distinctions from conventional "molecular medicine", with considerable emphasis on the advantages of nanomedicine. The in-depth investigation of Gd@C82(OH)22 undoubtedly provides a constructive reference for the development of other nanomedicines, especially in the fullerene family. The application of nanotechnology in the medical field definitely provides a promising and favorable future for improving the current status of cancer therapy.

Recent advances in single molecule magnetism of dysprosium-metallofullerenes

This article outlines the magnetic properties of single molecule magnets based on Dy-encapsulating endohedral metallofullerenes. The factors that govern these properties, such as the influence of different non-metal species in clusterfullerenes, the cage size, and cage isomerism are discussed, as well as the recent successful isolation of dimetallofullerenes with unprecedented magnetic properties. Finally, recent advances towards the organization of endohedral metallofullerenes in 1D, 2D, and 3D ordered structures with potential for devices are reviewed.

Two Dy(III) Single-Molecule Magnets with Their Performance Tuned by Schiff Base Ligands

To develop new lanthanide single-molecule magnets (SMMs), two new complexes of [Dy₂(MeOH)₂(HL¹)₂(NO₃)₂]·2MeOH (1) and [Dy₆(μ₃-OH)₂(L²)₂(HL²)₂(H₂L²)₂Cl₂(EtOH)₂]Cl₂·3EtOH·CH₃CN (2) were obtained by reacting Dy(NO)₃·6H₂O with 3-amino-1,2-propanediol in the presence of 2-hydroxynaphthaldehyde for 1 and by reacting DyCl₃·6H₂O with 1,1-di(hydroxymethyl)ethylamine in the presence of 2-hydroxynaphthaldehyde for 2, respectively, in which the Schiff base ligands of 3-(((2-hydroxynaphthaen-1-yl)methylene)amino)-propane-1,2-diol (H₃L¹) and 2-(β-naphthalideneamino)-2-(hydroxylmethyl)-1-propanol (H₃L²) were in situ formed. The two Dy(III) ions in 1 are linked by two O_alkoxy atoms of two (HL¹)^2- ligands to build a dinuclear skeleton. Complex 2 presents a nearly planar hexanuclear skeleton constructed from four edge-shared triangular Dy₃ units with the two peripheral Dy₃ units consolidated by two μ₃-O bridges and the two central Dy₃ units consolidated by one μ₃-O bridge. Obviously, they exhibit a different topological arrangement resulting from the linkage of the Schiff base ligands. Both of them are typical SMMs under zero dc fields, with a U_eff/ k_B value of 34 K for 1 and 40 K for 2, respectively. Multiple processes are involved in the relaxation processes of 1 and 2. The different SMM performances of the two titled complexes reveal a tuning effect of Schiff base ligands through tuning the coordination environments and topological arrangements of dysprosium(III) ions, which is supported by the theoretical calculations.