ru Sato

Semi-metallic single-component crystal of soluble La@C82 derivative with high electron mobility.

We prepared an organic conductor crystal having extremely high electron mobility, in which the adamantylidene (Ad) derivative of La@C(82) (an endohedral metallofullerene known as a n-type semiconductor) is aligned in an orderly fashion. The single-component crystal exhibits high electron mobility of μ > 10 cm(2) V(-1) s(-1) along the c axis under normal temperatures and pressures in the atmosphere, as shown by flash-photolysis time-resolved microwave conductivity (TRMC) measurements, which are the highest of reported organic conductors measured by TRMC. According to density functional calculations, the single crystal of La@C(82)Ad is semi-metallic, with a small band gap of 0.005 eV.

Covalently Linked Porphyrin–La@C82 Hybrids: Structural Elucidation and Investigation of Intramolecular Interactions†

The study of covalent and non-covalent photoactive hybrids continues to be of interest for developing photosynthetic and optoelectronic applications. To this end, C60 is recognized as an important building block owing to its rich redox properties and low reorganization energy in electron-transfer reactions. Hybrids of C60 with various photoactive and electroactive units have been studied comprehensively in the context of light harvesting, unidirectional energy transfer, and electron transfer. Recently, the unique structures and properties of endohedral metallofullerenes (EMFs), such as M3N@C80 (M = Sc, Lu) and M2@C80 (M = La, Ce), has led to their integration into photoactive hybrids in which improved or switchable interor intramolecular electron transfer events were realized. Another widely studied EMF is La@C2v–C82, which features a huge anionic p surface and an open-shell structure. Importantly, in comparison to C60 and the above-mentioned EMFs, La@C82 has more active redox properties, a broader absorption spectrum, a smaller band gap, and lower-lying excited state. 6] In this regard, incorporating La@C82 into multichromophoric systems is certainly worthy of consideration. In fact, recent efforts have exemplified the construction of supramolecular arrays of La@C82 and chromophores, such as porphyrins. However, covalently linked hybrids remain unexplored. A likely rationale includes the presence of multiple isomeric products that are formed in most reactions. Herein, we present three isomeric covalently linked 5,10,15,20-tetraphenylporphyrin (H2Por)–La@C82 hybrids, including their synthesis, electrochemistry, and spectroscopic and computational studies. Compared with non-covalent hybrids, the presence of a flexible linker between the two subunits is evidently crucial. It facilitates p–p attractions between the two subunits and therefore enhances intramolecular electronic interactions even in the ground state. Remarkable fluorescence quenching in all covalently linked hybrids is evidence of the occurrence of photoinduced intramolecular communication. The synthesis started with a thermal reaction (Scheme 1) involving La@C82 and a typical diazo precursor 1 that was used to synthesize the [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). Following a multistage separation using HPLC, three isomeric monoadducts (M1, M2, and M3) [11] were ultimately isolated as major products. Substitution of 1 by another precursor, 2, led to the synthesis of H2Por–La@C82 hybrids. In a similar way, three isomeric forms (M1Por, M2Por, and M3Por) were isolated as major products with lower yields.

Regioselective exohedral functionalization of La@C82 and its 1,2,3,4,5-pentamethylcyclopentadiene and adamantylidene adducts.

The first regioselective functionalization of La@C(82) by two different groups has been performed. Bis-adducts of La@C(82) with Cp* and adamantylidene were synthesized by using two different routes and characterized. Spectroscopic analysis and theoretical calculations reveal that the addition position is controlled by the charge density and p-orbital axis vector value of the fullerene cage.

Two Regioisomers of Endohedral Pyrrolidinodimetallofullerenes M2@Ih-C80(CH2)2NTrt (M=La, Ce; Trt=trityl): Control of Metal Atom Positions by Addition Positions

The two regioisomers of endohedral pyrrolidinodimetallofullerenes M(2)@I(h)-C(80)(CH(2))(2)NTrt (M = La, Ce; Trt = trityl) were synthesized, isolated, and characterized. X-ray crystallographic analyses of [6,6]-La(2)@I(h)-C(80)(CH(2))(2)NTrt and [6,6]-Ce(2)@I(h)-C(80)(CH(2))(2)NTrt revealed that the encapsulated metal atoms are located at the slantwise positions on the mirror plane that parallels the pyrrolidine ring. Paramagnetic NMR analyses of [6,6]- and [5,6]-Ce(2)@I(h)-C(80)(CH(2))(2)NTrt were also carried out to clarify the metal positions. As for the [6,6]-adduct, the metal positions obtained by paramagnetic NMR analysis agree well with the X-ray structure. In contrast, paramagnetic NMR analysis of the [5,6]-adduct showed that the two Ce atoms are collinear with the pyrrolidine ring. We also compared the observed paramagnetic effects of the pyrrolidinodimetallofullerenes with those of other cerium-encapsulating fullerene derivatives such as bis-silylated Ce(2)@I(h)-C(80) and a carbene adduct of Ce(2)@I(h)-C(80). We found that the metal positions can be explained by the electrostatic potential maps of the corresponding [6,6]- and [5,6]-adducts of [I(h)-C(80)(CH(2))(2)NTrt](6-). These findings clearly show that metal positions inside fullerene cages can be controlled by means of the addition positions of the addends. In addition, the radical anions of the pyrrolidinodimetallofullerenes were prepared by bulk controlled-potential electrolysis and characterized by X-band EPR spectral study.

Where does the metal cation stay in Gd@C2v(9)-C82? A single-crystal X-ray diffraction study.

Metal positions in endohedral metallofullerenes (EMFs) are of special importance because their molecular symmetry and intrinsic properties are strongly influenced by the location and motion of the encapsulated metals. X-ray analyses of the cocrystals of Gd@C(2v)(9)-C(82) with nickel(II) octaethylporphyrin [Ni(II)(OEP)] reveal that the Gd(3+) cation is off-center, being located under a hexagonal ring along the 2-fold axis of the C(2v)(9)-C(82) cage. This result is in sharp contrast to that of a previous study, showing that Gd@C(2v)(9)-C(82) has an anomalous endohedral structure, with the metal being positioned over a [6,6] bond, which is opposite to the hexagonal ring along the C(2) axis (Phys. Rev. B 2004, 69, 113412). In agreement with theoretical calculations and related studies, it is conclusive that the single rare-earth metal in M@C(2v)(9)-C(82) always tends to coordinate with the hexagonal ring along the 2-fold axis, instead of interacting with the [6,6] bond on the other end, regardless of the type of metal atom.

X-ray observation of a helium atom and placing a nitrogen atom inside He@C60 and He@C70.

Single crystal X-ray analysis has been used as a powerful method to determine the structure of molecules. However, crystallographic data containing helium has not been reported, owing to the difficulty in embedding helium into crystalline materials. Here we report the X-ray diffraction study of He@C60 and the clear observation of a single helium atom inside C60. In addition, the close packing of a helium atom and a nitrogen atom inside fullerenes is realized using two stepwise insertion techniques, that is, molecular surgery to synthesize the fullerenes encapsulating a helium atom, followed by nitrogen radio-frequency plasma methods to generate the fullerenes encapsulating both helium and nitrogen atoms. Electron spin resonance analysis reveals that the encapsulated helium atom has a small but detectable influence on the electronic properties of the highly reactive nitrogen atom coexisting inside the fullerene, suggesting the potential usage of helium for controlling electronic properties of reactive species.

Mechanistic study of the Diels-Alder reaction of paramagnetic endohedral metallofullerene: reaction of La@C82 with 1,2,3,4,5-pentamethylcyclopentadiene.

The reaction mechanism of the Diels-Alder reaction of paramagneticendohedral metallofullerene, La@C82, and 1,2,3,4,5-pentamethylcyclopentadiene was studied theoretically and experimentally. Theoretical calculations revealed that this reaction proceeds via a concerted mechanism that includes formation of a stable intermediate. The activation energy of a retro-Diels-Alder reaction was also studied experimentally, which is in good agreement with theoretical results.

Regioselective bis-functionalization of endohedral dimetallofullerene, La2@C80: extremal La-La distance.

Bis-functionalization of endohedral metallofullerene La(2)@C(80) by carbene addition is reported herein. Adducts were characterized using spectroscopic and single-crystal X-ray structure analyses. Crystallographic data for bisadduct La(2)@C(80)(CClPh)Ad (3, Ad = adamantylidene) revealed that both carbene additions occur at the 6,6-bond junction on the C(80) cage with ring cleavages and that La atoms are positioned collinearly with spiro carbons. It is noteworthy that the La-La distance in 3 is highly elongated by carbene bis-functionalization compared to the distance in pristine La(2)@C(80) and reported functionalized derivatives. The metal positions were confirmed through density functional calculations.

Tunable Charge-Transport Properties of Ih-C80 Endohedral Metallofullerenes: Investigation of La2@C80, Sc3N@C80, and Sc3C2@C80

Fullerene crystals or films have drawn much interest because they are good candidates for use in the construction of electronic devices. The results of theoretical calculations revealed that the conductivity properties of I(h)-C(80) endohedral metallofullerenes (EMFs) vary depending on the encapsulated metal species. We experimentally investigated the solid-state structures and charge-carrier mobilities of I(h)-C(80) EMFs La(2)@C(80), Sc(3)N@C(80), and Sc(3)C(2)@C(80). The thin film of Sc(3)C(2)@C(80) exhibits a high electron mobility μ = 0.13 cm(2) V(-1) s(-1) under normal temperature and atmospheric pressure, as determined using flash-photolysis time-resolved microwave conductivity measurements. This electron mobility is 2 orders of magnitude higher than the mobility of La(2)@C(80) or Sc(3)N@C(80).

Thermal Carbosilylation of Endohedral Dimetallofullerene La2@Ih-C80 with Silirane

Thermal carbosilylation of endohedral dimetallofullerene La(2)@I(h)-C(80) with silirane (silacyclopropane) is reported herein for the first time. Two diastereomers of the carbosilylated La(2)@I(h)-C(80) have been isolated and characterized. The fascinating molecular structure of one diastereomer of the carbosilylated derivatives has been determined unambiguously using X-ray crystallographic analysis. Detailed characteristics of the molecular structures including their metal atom movements have also been revealed using NMR spectroscopic studies and computational calculations. Results revealed that two La atoms move dynamically inside the carbon sphere. Furthermore, electrochemical study has demonstrated that carbosilylation is effective to fine-tune the La(2)@I(h)-C(80) electronic properties.