Shuaifeng Hu

Abstract:

Six dierbium carbide endohedral metallofullerenes have been synthesized and chromatographically isolated. Single-crystal X-ray diffractometry unambiguously ascertains their structures as Er₂C₂@C_2v(5)-C₈₀, Er₂C₂@C_s(6)-C₈₂, Er₂C₂@C_s(15)-C₈₄, Er₂C₂@C_2v(9)-C₈₆, Er₂C₂@C_s(15)-C₈₆, and Er₂C₂@C_s(32)-C₈₈, respectively. The Er···Er distances of the major erbium sites inside the C_s(6)-C₈₂, C_2v(5)-C₈₀, C_s(15)-C₈₄, C_s(15)-C₈₆, C_2v(9)-C₈₆, and C_s(32)-C₈₈ cages are 3.801, 3.860, 4.062, 4.066, 4.307, and 4.372 Å, respectively, which show a linear tendency with an increase in the major axis of the fullerene cages (8.064, 8.238, 8.508, 8.582, 8.815, and 8.953 Å, respectively). Furthermore, the electrochemical and molecular orbital analyses reveal that the redox chemistry of the Er₂C₂@C_80-88 isomers is associated with the carbon cage, which is different from the situations found for typical dimetallofullerenes, such as Y₂@C₈₂, Er₂@C_82-84, and Lu₂@C_82,86 isomers, which show metal-dependent oxidation processes, indicating the importance of C₂ insertion in carbide cluster metallofullerenes.

Abstract:

Diels-Alder reactions of cyclopentadiene to C_2v(19 138)-C₇₆ and YNC@C_2v(19 138)-C₇₆ violating the isolated pentagon rule have been systematically studied by means of density functional theory calculations. As for the free fullerene, the pentalene-type [5,5]-bond in the adjacent pentagon pair is the most favorable from thermodynamic and kinetic viewpoints, which is attributed to the highly strained carbon atoms accompanied by the suitable lowest unoccupied molecular orbital shape with a large distribution to interact with cyclopentadiene. Upon encapsulating the YNC cluster, a corannulene-type [5,6]-bond and a pyracylene-type [6,6]-bond become the two most reactive addition sites under thermodynamic and kinetic conditions, which possess similar reaction energies and energy barriers. Especially, the [5,6]-bond exhibits a larger reaction energy and a lower energy barrier than that on the free fullerene, which should be ascribed to its shorter bond length and larger π-orbital axis vector value after trapping the metallic cluster. The suitable unoccupied molecular orbital lobes with large distributions on the [5,6]- and [6,6]-bonds are also an advantage of cycloadditions. This work presents the first example that the most favorable addition site is remote from the adjacent pentagon pair in the fullerene cage after encapsulating a metallic cluster.

Abstract:

For endohedral metallofullerenes (EMFs), that is, fullerenes encapsulating metallic species, cage size is known to be an important factor for cluster configuration adoption; however, the impact of the cage shape on the cluster geometry fitting remains poorly understood. Herein, for the first time, four dierbium-carbide EMFs with C₉₀ cages, namely, Er₂C₂@C₂(43)-C₉₀, Er₂C₂@C₂(40)-C₉₀, Er₂C₂@C₂(44)-C₉₀, and Er₂C₂@C₁(21)-C₉₀, were successfully synthesized and fully characterized using a combination of mass spectrometry, single-crystal X-ray diffractometry, vis-NIR, Raman and photoluminescence spectroscopies, and cyclic voltammetry. In particular, the fullerene cages of C₂(43)-C₉₀ and C₂(44)-C₉₀ are crystallographically identified for the first time. Interestingly, the ErEr distance of the major sites in Er₂C₂@C₂(43)-C₉₀, Er₂C₂@C₂(40)-C₉₀, Er₂C₂@C₂(44)-C₉₀, and Er₂C₂@C₁(21)-C₉₀ is 3.927, 4.058, 4.172, and 4.651 Å, respectively, which increases gradually with an increase in the major axis of the cage. Moreover, the bond length of the inner C₂-unit decreases progressively with an increase in the ErEr distance, indicating that the inserted C₂-unit can serve as a molecular spring to support the strong metal-cage interactions within cages with the same size but different shapes. Hence, the role of cage shape on the cluster configuration is unveiled safely for the as-obtained Er₂C₂@C₉₀ isomers.

Abstract:

Successful isolation and characterization of a series of Er-based dimetallofullerenes present valuable insights into the realm of metal-metal bonding. These species are crystallographically identified as Er₂ @C_s (6)-C₈₂ , Er₂ @C_3v (8)-C₈₂ , Er₂ @C₁ (12)-C₈₄ , and Er₂ @C_2v (9)-C₈₆ , in which the structure of the C₁ (12)-C₈₄ cage is unambiguously characterized for the first time by single-crystal X-ray diffraction. Interestingly, natural bond orbital analysis demonstrates that the two Er atoms in Er₂ @C_s (6)-C₈₂ , Er₂ @C_3v (8)-C₈₂ , and Er₂ @C_2v (9)-C₈₆ form a two-electron-two-center Er-Er bond. However, for Er₂ @C₁ (12)-C₈₄ , with the longest Er⋅⋅⋅Er distance, a one-electron-two-center Er-Er bond may exist. Thus, the difference in the Er⋅⋅⋅Er separation indicates distinct metal bonding natures, suggesting a distance-dependent bonding behavior for the internal dimetallic cluster. Additionally, electrochemical studies suggest that Er₂ @C_82-86 are good electron donors instead of electron acceptors. Hence, this finding initiates a connection between metal-metal bonding chemistry and fullerene chemistry.