Ab initio investigations of the charge transport properties of endohedral M@C_(20)(M=Na and K)metallofullerenes

Using density functional theory and quantum transport calculations based on nonequilibum Green＇s function formalism, we investigate the charge transport properties of endohedral M@C20（M = Na and K） metallofullerenes. Our results show that the conductance of C20 fullerene can be obviously improved by insertion of alkali atom at its centre. Both linear and nonlinear sections are found on the Ⅰ-Ⅴ curves of the Au-M@C20-Au two-probe systems. The novel negative differential resistance behaviour is also observed in Na@C20 molecule but not in K@C20.

High-Yield Synthesis of Endohedral Metallofullerenes Y@C_(2n) and Y_2@C_(2n)

A series of yttrium metallofullerenes some of them are first reported. have beensynthesized by the DC, are discharge method at high helium pressure. Mass spectra results showthat the contents of metallofullerenes are very' high both in primary soot and in CS2 or DMF extract.and Y@C82, with ca 85% purity is obtained through column chromatographic isolation.

High-Yield Synthesis and Extraction of Endohedral Metallofullerenes Dy@C_(2n)

The successful encapsulation of dysprosium(Dy) into fullerene cages by activating the Dy2O3, containing graphite rods in situ 'back-burning' carbonarc evaporation with a high-yield of pyridine extraction technique is reported.

Intensity Exaggeration of Endohedral Metallofullerenes in Laser Desorption-Ionization Time-of-Flight Mass Spectrometry

The laser-desorption-ionization time-of-flight mass spectrometry and desorption-electron-ionization mass spectrometry were employed for the characterization of metallofullerenes extract. it was found that the relative intensities of metallofullerenes in this positive-ion, negative-ion LD-TOF MS and DEI MS were much different. This phenomenon should have relationship with the peculiar ionization energies and electron affinities of metallofullerenes.

Synergistic modulation of spin and fluorescence signals in a nano-Saturn assembled by a metallofullerene and cycloparaphenylene nanohoop

Spin-based interdisciplinary research has attracted considerable attention,and various applications in magnetic memory,quantum science,and precision measuring technology have been reported.In this study,we induced a fluorescence property in a spin-active molecule by supramolecular assembly and realized a synergistic modulation of its spin and fluorescence properties.A Saturn-shaped supramolecular complex was synthesized using a spin-active metallofullerene Sc_(3)C_(2)@C80 with a fluorescent nanohoop of tetra-benzothiadiazole-based[12]cycloparaphenylene(TB[12]CPP),and its spin and fluorescence properties were comprehensively investigated.Temperature-dependent electron paramagnetic resonance(EPR)spectroscopy and fluorescence analyses were conducted.Synchronous changes in the EPR signals and fluorescence peaks were discovered in the temperature range of 170–290 K.Based on nuclear magnetic resonance observations and theoretical calculations,a temperature-dependent host–guest interaction between Sc_(3)C_(2)@C_(80)and a nanohoop was demonstrated,which explained the synchronous changes in the EPR signals and fluorescence peaks for Sc_(3)C_(2)@C_(80)⊂TB[12]CPP.The application of Sc_(3)C_(2)@C_(80)as a molecular spin system to probe the host–guest interaction was also evaluated.These results show that the supramolecular assembly can be used to design advanced spin systems coupled with optical and magnetic behaviors based on paramagnetic and luminescent molecules.

Luminescent single-molecule magnet of metallofullerene DyErScN@Ih-C80

Magneto-luminescent molecules have significant applications in data storage and quantum computing.However,design of these bi-functional molecules coupled with magnetic behavior and photoluminescence is still challenging.In this work,we report a metallofullerene DyErScN @In-C80 exhibiting single-molecule magnet (SMM) behavior and near-infrared emission.For DyErScN @Ih-C80,two functional lanthanide metal ions of Dy^3+(SMM function) and Er^3+(luminescent function) are integrated inside a fullerene cage using a trimetallic nitride template,and its structure has been unambiguously characterized by single-crystal X-ray diffraction.Magnetic measurements revealed that DyErScN @Ih-C80 behaves as a SMM with a blocking temperature up to 9 K resulting from the intramolecular magnetic interaction between Dy^3+ and Er^3+ ions.Moreover,DyErScN @In-C80 exhibits temperature-dependent near-infrared emission around 1.5 pm with multiple splitting peaks from Er^3+,which arises from the influence of Dy^3+ ion.This study provides a new strategy to synthesize new magneto-luminescent molecule materials.

Covalently bonded two spin centers of paramagnetic metallofullerene dimer

Paramagnetic endohedral metallofullerenes with well protected unpaired spin have potential applications in molecular-scale qubit processing and magnetoreception system. In this study, a paramagnetic metallofullerene Sc_(3)C_(2)@C_(80) dimer with covalently bonded two spin centers was synthesized. Electron paramagnetic resonance (EPR) results further revealed the varied spin-nuclei couplings and paramagnetic property for Sc_(3)C_(2)@C_(80) dimer. Briefly, the Sc_(3)C_(2)@C_(80) dimer in toluene solution shows EPR hyperfine splittings originating from the spin-Sc couplings. However, the Sc_(3)C_(2)@C_(80) dimer in solid state shows the disappearance of hyperfine structure and a single EPR signal caused by its two-spin-center structure. The transformation of EPR signals can be further finely modulated by controlling the dynamic motion of Sc_(3)C_(2)@C80 dimer in chloronaphthalene. The Sc_(3)C_(2)@C_(80) dimer with two spin centers possesses varied paramagnetic properties, demonstrating its potential as new magnetic material.

Formation of substitutional metallofullerenes by laser ablation of externally doped fullerenes C_(60)M_x(M=Sm,Pt,Ni and Rh)

Photofragmentation study of metal fullerides C60Mx (M=Sm, Pt, Ni and Rh) by excimer laser ablation-TOF mass spectrometry shows that metallofullerenes C2nM and C2n+1M formed in both the positive and negative ionic modes. The isotopic distributions of the metallofullerenes C2nM and C2n+1M are consistent with the calculated spectra based on the natural abundance of isotopes of C and M, confirming the formation of metallofullerenes. The metal atom is sup-posed to be incorporated into the network of the fullerene cage to replace one carbon atom of the cage forming substi-tutional metallofullerene. Odd-numbered high carbon clusters are observed in our laser ablation study of all the metal fullerides in the negative ion channel. Evolution of mass spectrum with irradiation laser shots shows that the formation of the substitutionally doped fullerenes is closely related to the production of metal carbide (MC). The structures, as well as formation mechanism, of metallofullerenes C2n+1M and C2nM with even and odd

Managing interfacial properties of planar perovskite solar cells using Y_(3)N@C_(80)endohedral metallofullerene

Fullerene derivatives have a wide range of applications in perovskite solar cells(PSCs),such as electron transport layers(ETLs),interfacial modifiers,and additives.However,there have been few studies of the use of endohedral metallofullerenes(EMFs)to improve the performance of PSCs.Here,a novel EMF(Y_(3)N@C_(80))was synthesized and used as an interfacial modifier in PSC devices based on a SnO_(2)ETL.Energy level mismatches and detrimental carrier recombination have been observed in devices with a pristine SnO_(2)ETL,but these issues are alleviated with the assistance of Y_(3)N@C_(80).A significant increase in open-circuit voltage from 1.106 V(SnO_(2))to 1.14 V(SnO_(2)-Y_(3)N@C_(80)),an increase in power conversion efficiency from 20.59%to 21.66%,and a marked reduction in hysteresis were observed,which were attributed to the more suitable conduction band energy levels and more effective electron extraction at the SnO_(2)-Y_(3)N@C_(80)/perovskite interface.In addition,the stability of the target devices was improved,which may be due to the hydrophobicity of Y_(3)N@C_(80)and a reduction in trap states.

Studies on extracting solutions of endohedral rare-earth metallofullerenes by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Thirteen extracting solutions of rare-earth metallofullerenes containing La,Ce,Pr,Nd Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm and Yb respectively have been investigated by means of matrix-assisted laser desorpuon/ ionization time-of-flight mass spectrometry.The influences of the positive-ion/negative-ion mode,laser intensity,ma trix and mass discrimination to the analytical results are studied,based on which the optimal analytical conditions have been determined.The results show that the extracting solutions contain large quantities of rare-earth metallofullerenes besides empty fullerenes.On the basis of comparing their relative intensities,the different structure stabilities and solubilities of metallofullerenes with different rare-earth metals encapsulated into the fullerene cages,as well as some possible reasons to those differences,are discussed.

Highly delocalized endohedral metal in Gd@C2v（9）-C82 metallofullerenes co-crystallized with α-Se

A new Gd@C2v（9）-C82·2.5（S8）·0.5（CS2） co-crystal was prepared for the first time and characterized by single-crystal X-ray diffraction （XRD）. The analysis dearly showed that, even though the C2v（9）-C82 cage is fully ordered, the endohedral Gd atoms are highly disordered. This result indicates the presence of highly delocalized endohedral Gd atoms, which has never been reported before. Density functional theory （DFT） calculations were used to rationalize the XRD results. The calcula- tions reveal the presence of two local energy minima, a and b, with the latter existing as four conformers b1-b4. Whereas the energy difference between the two minima is calculated only - 10 kcal/mol, their interconversion is almost impossible due to a high energy barrier, of up to 35.98 kcal/mol. This suggests the existence of multiple low-energy positions for the endohedral Gd atom. In addition, a remarkable electron transfer from the C2d9）-C82 cage to the S8 moieties was demonstrated, which might result in a modified endohedral environment and further contribute to the occurrence of delocalized endohedral Gd atoms.

Studies on the Luminescence Property of Yttrium-Based Metallofullerenes

Endohedral metallofullerenes(EMFs) exhibit various properties due to their multiple combinations between internal metals and outer carbon cages. Among them, yttrium-based metallofullerenes have attracted much attention due to their luminescence properties. For example,YN@Cis distinguished by its photoluminescence(PL) properties with a small energy gap between the lowest singlet states(S) and the triplet excited states(T) in YN@C, allowing reverse intersystem crossing(RISC) of T→Sand resulting in thermally activated delayed fluorescence(TADF). In addition, the PL intensity, lifetime, and quantum yield(QY) of YN@Call depend on the molecular structure and surrounding environment. Typically, modulation of the PL properties can be achieved by replacing the yttrium metal inside the carbon cage as well as by modifying the carbon cage externally.Here, we focus on the luminescence properties of yttrium-based metallofullerenes, summarize recent research advances, and predict their future development.

笼内金属富勒烯的合成与分析

自1985年,Smalley等人首次在飞行时间质谱仪中检测到C60以来[1],富勒烯碳原子族的研究便不断深入,最初发现的激光蒸发含稀土化合物的石墨只能得到微量的金属富勒烯,仅限于质谱检测,直到1990年,Kratschmer等人采用石墨电子弧放电首次得到宏观量的富勒烯[2],才使得富勒烯研究进入了实质性的研究阶段.……

Coverage-dependent Orientations of Dy@C82 Molecules on Au（111） Surface

The adsorption and molecular orientation of Dy@Cs2 isomer I on Au（111） has been investigated using ultrahigh-vacuum scanning tunneling microscopy at 80 K. At low coverages, the Dy@Cs2 molecules tend to grow along the step edges of Au（111）, forming small clusters and molecular chains. Adsorption of Dy@Cs2 on the edges is dominated by the fullerene-substrate interaction and presents various molecular orientations. At higher coverages, the Dy@Cs2 is found to form ordered islands consisting of small domains of equally oriented molecules. The Dy@Cs2 molecules in the islands prefer the adsorption configurations with the major C2 axis being approximately parallel to the surface of the substrate. Three preferable orientations of the Dy@Cs2 molecules are found in a two-dimensional hexagonal close packed overlayer. These observations are attributed to the interplay of the fullerene-substrate interaction and dipole-dipole interaction between the metallofullerenes.

DFT Studies on Non-IPR C_(68) and Endohedral Fullerene Sc_3N@C_(68)

Density functional theory （DFT） calculations on two isomers of C68 with the minimal number of fused pentagon pairs, its anions and Sc3N as well as Sc3N@C68 （6140） metallofullerene were carded out at the B3LYP/6-31G^＊ level. The optimized configurations and electrostatic potential distributions have been obtained. The calculated results show that the electrostatic potentials of C68 （6140） inside the sphere have three minima in the middle of the double bonds at fusion of two hexagonal rings. In contrast, potential minimum Vmin（r） of C68 （6275） inside the sphere occurs at the center of the sphere. Concerning the two isomers of C68, the largest regions with the most negative MEP outside the sphere are both localized in the neighborhood of pentagon-pentagon vertex fusions. They constitute the most probable active sites in chemical reactions. Our results present a reasonable explanation for the bonding between scandium atoms and fullerene cage.

Theoretical Study on Molecular Electrostatic Potential of C_(78)

Density functional theory （DFT） was applied at the B3LYP/6-31G^＊ level to investigate the relative stability of the five fullerene isomers as well as the anions of C78. Full geometry optimization was carried out and distributions of electrostatic potential were calculated. The results showed that the C78（D3h′） cage was the most stable for C78^q-（ q = 2, 4, 6）, and the potential minimum Vmin（r） inside the sphere of C78（Dzh′） was the biggest one among the five isomers of C78. So C78（Dzh′） were electrons from the scandium atoms that were easier to accept than the other four isomers. On the other hand, MEP maps inside the sphere of C78（Dzh′） had three minima near the three vertexes. Each vertex was formed by the intersection of the three hexagons. Our results allowed a possible explanation for the bonding between the scandium atoms and the fullerene cage.

Scanning tunneling microscopy study of molecular growth structures of Gd@C_(82) on Cu(111)

The coverage and temperature-dependent nucleation behaviors of the Gd@C82 metallofullerenes on Cu（111） have been studied by low-temperature scanning tunneling microscopy （LT-STM） in detail. Upon molecular deposition at low temperature, Gd@C82 molecules preferentially decorate the steps and nucleate into single layer islands with increasing coverage. Further annealing treatment leads some of the Gd@C82 molecules to assemble into bright and dim patches, which are correlated to the adsorption induced substrate reconstruction. Upon sufficient thermal activation, Gd@C82 molecules sink into the Cu（111） surface one-copper-layer-deep, forming hexagonal close-packed molecular islands with intra-molecular details observed as striped patterns. By considering the commensurability between the Gd@C82 nearest-neighbor distance and the lattice of the underlying Cu（111）, we clearly identified two kinds of in-plane molecular arrangements as （19（1/2）×19（1/2））R23.4°and （19（1/2）×19（1/2））R36.6°with respect to Cu（111）. Within the assembled Gd@C82 molecular, island molecules with dim–bright contrast are spatially distributed, which may be modulated by the preexisted species on Cu（111）.

Transition Metal/Lanthanide-Nitrogen Double Bonds Co-stabilized in a Carbon Cage

Metal−nitrogen double bonds have been commonly reported for conventional metal complexes,but the coexistence of both transition metal−nitrogen and lanthanide−nitrogen double bonds bridged by nitrogen within one compound has never been reported.Herein,by encapsulating a ternary transition metallanthanide heteronuclear dimetallic nitride into a C_(84) fullerene cage,transition metal−nitrogen and lanthanide-nitrogen double bonds are costabilized simultaneously within the as-formed clusterfullerene TiCeN@C_(1)(12)-C_(84),which is a representative heteronuclear dimetallic nitride clusterfullerene.Its molecular structure was unambiguously determined by single-crystal X-ray diffraction,revealing a slightly bentμ2-bridged nitride cluster with short Ti−N(1.761Å)and Ce−N(2.109Å)bond lengths,which are comparable to the corresponding Ti=N and Ce=N double bonds of reported metal complexes and consistent with the theoretically predicted values,confirming their coexistence within TiCeN@C_(1)(12)-C_(84).Density functional theory(DFT)calculations unveil three-center two-electron(3c-2e)bonds delocalized over the entire TiCeN cluster,which are responsible for costabilization of Ti�N and Ce�N double bonds.An electronic configuration of Ti4+Ce^(3+)N^(3−)@C_(84)^(4−)is proposed featuring an intramolecular four-electron transfer,drastically different from the analogous actinide dimetallic nitride clusterfullerene(U_(2))^(9+)N^(3−)@C_(80)^(6−)and trimetallic nitride clusterfullerene(Sc_(2))^(6+)Ti^(3+)^(N3−)@C_(80)^(6−),indicating the peculiarity of 4-fold negatively charged fullerene cage in stabilizing the heteronuclear dimetallic nitride cluster.

Novel carbon nanohybrids as highly efficient magnetic resonance imaging contrast agents

Novel carbon nanohybrids based on unmodified metallofullerenes have been successfully fabricated for use as a new magnetic resonance imaging （MRI） contrast agent. The nanohybrids showed higher R1 relaxivity and better brightening effect than Gd@C82（OH）x, in Tl-weighted MR images in vivo. This is a result of the proton relaxivity from the original gadofullerenes, which retained a perfect carbon cage structure and so might completely avoid the release of Gd^3＋ ions. A ＂secondary spin-electron transfer＂ relaxation mechanism was proposed to explain how the encaged Gd^3＋ ions of carbon nanohybrids interact with the surrounding water molecules. This approach opens new opportunities for developing highly efficient and low toxicity MRI contrast agents.

Synthesis of metallic silicide fullerenes and the characteristics thereof by mass spectrometry

Direct current arc discharge is used for the study on the synthesis of metallo-fullerenes (MFs) to discover whether there exist metallic silicide fullerenes and silicon fullerenes. The resultant components are isolated by the multistage high-performance liquid chromatography (HPLC) and analyzed with the Time-of-Flight (TOF) mass spectrometry. Results show that there exist fullerenes such as SiC69, YSi2C64, YSi2C78, Y3Si2C78 as well as Y2Si2C90 which are structurally similar to (Y2C2)@C82.