Synthesis and Crystal Structure of Li⁺@Fluoreno[60]fullerene: Effect of Encapsulated Lithium Ion on Electrochemistry of Spiroannelated Fullerene

The reaction of [Li⁺@C₆₀]­TFSI^– (TFSI = bis­(trifluoromethanesulfonyl)­imide) with 9-diazofluorene directly produced a [6,6]-adduct of lithium-ion-containing fluoreno[60]­fullerene, [6,6]-[Li⁺@C₆₀(fluoreno)]­TFSI^–, which was crystallographically characterized. Cyclic voltammetry of the compound showed a reversible one-electron reduction wave at −0.51 V (vs Fc/Fc⁺) and an irreversible reduction wave for the second electron. The latter was attributed to opening of the three-membered ring due to strong stabilization of the resulting sp³-carbanion by the encapsulated Li⁺ and formation of a 14π-electron aromatic fluorenyl anion

Crystallographic information file of [Li+@C60−](NiOEP)∙CH2Cl2 at 400 K from Structure of [60]fullerene with mobile lithium cation inside

Crystallographic information file of [Li+@C60−](NiOEP)∙CH2Cl2 at 400

Crystallographic information file of [Li+@C60](TFSI−)∙CH2Cl2 at 150 K from Structure of [60]fullerene with mobile lithium cation inside

Crystallographic information file of [Li+@C60](TFSI−)∙CH2Cl2 at 150

Crystallographic information file of [Li+@C60](TFPB−)∙C4H10O at 260 K from Structure of [60]fullerene with mobile lithium cation inside

Crystallographic information file of [Li+@C60](TFPB−)∙C4H10O at 260

Structure of Tm@C₈₂(I) Metallofullerene by Single-Crystal X‑ray Diffraction Using the 1:2 Co-Crystal with Octaethylporphyrin Nickel (Ni(OEP))

The molecular structure of Tm@C₈₂ (isomer I) is revealed by single-crystal X-ray diffraction of the 1:2 cocrystal with nickel octaethylporphyrin (Ni­(OEP)). A rotational movement of Tm@C₈₂(I) molecule in the 1:1 cocrystal is dramatically suppressed by the coordination of two Ni­(OEP) ligands in the 1:2 cocrystal. The structure of Tm@C₈₂(I) in the crystal is explained by the orientation disorder with two different orientations. The so-obtained carbon cage structure is <i>C</i>_<i>s</i>(6)–C₈₂. The restricted molecular orientations of Tm@C₈₂(I) in the 1:2 cocrystal are achieved by the molecular dipole moment of Tm@C₈₂(I) that interacts with two Ni­(OEP) ligands. The present study suggests that the intermolecular interactions can reduce the degree of freedom in the orientation of spherical metallofullerene molecules in the crystals and complexes

Kinetic Study of the Diels–Alder Reaction of Li⁺@C₆₀ with Cyclohexadiene: Greatly Increased Reaction Rate by Encapsulated Li⁺

We studied the kinetics of the Diels–Alder reaction of Li⁺-encapsulated [60]­fullerene with 1,3-cyclohexadiene and characterized the obtained product, [Li⁺@C₆₀(C₆H₈)]­(PF₆^–). Compared with empty C₆₀, Li⁺@C₆₀ reacted 2400-fold faster at 303 K, a rate enhancement that corresponds to lowering the activation energy by 24.2 kJ mol^–1. The enhanced Diels–Alder reaction rate was well explained by DFT calculation at the M06-2X/6-31G­(d) level of theory considering the reactant complex with dispersion corrections. The calculated activation energies for empty C₆₀ and Li⁺@C₆₀ (65.2 and 43.6 kJ mol^–1, respectively) agreed fairly well with the experimentally obtained values (67.4 and 44.0 kJ mol^–1, respectively). According to the calculation, the lowering of the transition state energy by Li⁺ encapsulation was associated with stabilization of the reactant complex (by 14.1 kJ mol^–1) and the [4 + 2] product (by 5.9 kJ mol^–1) through favorable frontier molecular orbital interactions. The encapsulated Li⁺ ion catalyzed the Diels–Alder reaction by lowering the LUMO of Li⁺@C₆₀. This is the first detailed report on the kinetics of a Diels–Alder reaction catalyzed by an encapsulated Lewis acid catalyst rather than one coordinated to a heteroatom in the dienophile

A Structural Diagnostics Diagram for Metallofullerenes Encapsulating Metal Carbides and Nitrides

Systematic structural studies of 24 different kinds of endohedral metallofullerenes, M_<i>x</i>C_2<i>n</i> (M = La, Y, Sc, Lu, Ti, Eu, Er, Hf, Sc₃N; 34 ≤ <i>n</i> ≤ 43), as 1:1 cocrystals with solvent toluene molecules have been carried out using synchrotron radiation powder diffraction. Thirteen of the 24 molecular structures, including five metal carbides, one metal nitride endohedral fullerene, and one hollow fullerene, have been determined by a combination of the maximum entropy method and Rietveld refinement of the X-ray diffraction data obtained. We have found that the volume for one fullerene and one toluene molecule depends linearly on the number of carbon atoms in the fullerene cage. Fifteen different kinds of metal carbide endohedral fullerenes have been identified, which can be structurally characterized from the obtained lattice constants using only this linear dependence. The linear dependence found in the present study provides a metallofullerene diagnostics diagram that may have universal importance for structural characterization of the so-called cluster endohedral fullerenes

Perfectly Ordered Two-Dimensional Layer Structures Found in Some Endohedral Metallofullerenes

A two-dimensional (2D) arrangement of metallofullerenes for both M@C₈₂ (isomer I) (M = Y, La, Ce, Pr) and (M₂C_<i>y</i>)@C₈₂ (isomer III) (M = Er, <i>y</i> = 0, 2; M = Sc, <i>y</i> = 2) is crystallized with a 1:2 fullerene/toluene molecular ratio. The determined crystal is a 2D layered structure, which is composed of metallofullerene layers sandwiched by the toluene layers. Although the M@C₈₂(I) arrangement in a 1:1 crystal is almost identical to that of (M₂C_<i>y</i>)@C₈₂(III), the M@C₈₂(I) arrangement in a 1:2 crystal is different from (M₂C_<i>y</i>)@C₈₂(III). It is found that the difference of the molecular arrangement strongly correlates with an orientation of metallofullerenes in a 2D layer. Our findings suggest the existence of a subtle but important interaction between the confined atoms/molecules and the solvent molecules/toluene through the carbon cage, which leads to a guiding principle of crystallization control with a solvent ingredient for metallofullerenes