Observation of an all-boron fullerene

Journal name:
Nature Chemistry
Year published:
Published online


After the discovery of ​fullerene-C60, it took almost two decades for the possibility of ​boron-based fullerene structures to be considered. So far, there has been no experimental evidence for these nanostructures, in spite of the progress made in theoretical investigations of their structure and bonding. Here we report the observation, by photoelectron spectroscopy, of an all-boron fullerene-like cage cluster at B40 with an extremely low electron-binding energy. Theoretical calculations show that this arises from a cage structure with a large energy gap, but that a quasi-planar isomer of B40 with two adjacent hexagonal holes is slightly more stable than the fullerene structure. In contrast, for neutral B40 the fullerene-like cage is calculated to be the most stable structure. The surface of the all-boron fullerene, bonded uniformly via delocalized σ and π bonds, is not perfectly smooth and exhibits unusual heptagonal faces, in contrast to ​C60 fullerene.

At a glance


  1. Photoelectron spectrum of the B40− cluster and comparison with simulated spectra.
    Figure 1: Photoelectron spectrum of the B40 cluster and comparison with simulated spectra.

    a, Experimental spectrum at 193 nm (6.424 eV) detachment photon energy. The inset for the weak band X′ at ~2.6 eV binding energy is magnified eight times to show the details. The labels X′, X, A, B, C and D denote observed photodetachment transitions from the B40 anion to the final electronic states of neutral B40. The X′ band represents an isomer of B40 with an extremely low electron-binding energy compared with those of all known boron clusters, which suggests a cluster with an unusual structure. b, Simulated spectrum at the PBE0 level, based on the quasi-planar structure 1 (Cs, 2A′). The major experimental bands (X, A, B, C and D) are well reproduced by the simulated spectrum. c, Simulated spectrum based on the cage-like fullerene structure 2 (D2d, 2B2) that shows the large energy gap between the first and second bands. Band X′ with a low binding energy is well reproduced by the D2d cage structure and no planar structures would yield such a feature of low binding energy. The simulations were done by fitting the distributions of calculated vertical detachment energies at the PBE0 level with unit-area Gaussian functions of 0.1 eV half-width. a.u., arbitrary units.

  2. Top and side views of the global minimum and low-lying isomers of B40− and B40 at the PBE0/6-311+G* level.
    Figure 2: Top and side views of the global minimum and low-lying isomers of B40 and B40 at the PBE0/6-311+G* level.

    The simulated photoelectron spectra from the anionic species of these two structures are compared with the experimental data in Fig. 1. 1 (Cs) is the quasi-planar global minimum and 2 (D2d) is the nearly degenerate low-lying fullerene-like cage structure of the negatively charged B40. 3 (Cs) is the low-lying isomer and 4 (D2d) is the global minimum of the neutral B40. There is very little structural change between the anion and the neutral cluster in each isomer. Detailed structural parameters for both the anions and the neutrals are given in Supplementary Table 1. The symbols in parentheses represent the spectroscopic states of each species. The hexagonal face of the top view of the cage structure is shaded in purple, along with four B6 triangles shaded in grey. The bottom half of the B40 cage is identical with the top half, but rotated by 90°. In the side view of the cage structure, the heptagonal face is shaded in purple along with four B6 triangles shaded in grey. There are two hexagonal and four heptagonal faces on the cage surface.

  3. Configurational energy spectra at the PBE0/6-311+G* level.
    Figure 3: Configurational energy spectra at the PBE0/6-311+G* level.

    a, B40. b, B40. The energies of the global minima are taken to be zero. More detailed isomer populations are given in Supplementary Figs 2 and 3 for B40 and B40, respectively, as well as energetic information calculated at different levels of theory. Black, quasi-planar structures; red, fullerene-like cages; violet, double-ring tubular structures; blue, triple-ring tubular structure.

  4. Results of chemical bonding analyses for the B40 fullerene.
    Figure 4: Results of chemical bonding analyses for the B40 fullerene.

    The analyses were done using the AdNDP method39. Each lobe in the five frames represents a multicentre two-electron bond, with the occupation number (ON) given below each frame. There are 40 three-centre two-electron σ bonds, given as 40 × 3c–2e σ bonds, and eight six-centre two-electron σ bonds (8 × 6c–2e σ bonds). The eight six-centre σ bonds are localized mainly on the central B3 triangle of each grey-shaded B6 triangle in 4 (Fig. 2). Hence, there is essentially one 3c–2e delocalized σ bond for each of the 48 triangular faces of the B40 cage. The π bonds are classified using the cage surface as the nodal plane. There are 12 delocalized multicentre two-electron π bonds along the interwoven double-boron chains, including four five-centre, four six-centre and four seven-centre π bonds. All the 120 valence electrons of the B40 cage form delocalized bonds (48 σ and 12 π bonds) uniformly over the surface of the cage without any classical two-centre two-electron localized bonds. This bonding pattern of the all-boron B40 fullerene cage is extraordinary and unprecedented among all known boron clusters.


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Author information


  1. Institute of Molecular Science, Shanxi University, Taiyuan 030006, China

    • Hua-Jin Zhai,
    • Qiang Chen,
    • Hui Bai,
    • Wen-Juan Tian,
    • Hai-Gang Lu,
    • Yan-Bo Wu,
    • Yue-Wen Mu &
    • Si-Dian Li
  2. Department of Chemistry & Key Laboratory of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China

    • Ya-Fan Zhao,
    • Han-Shi Hu &
    • Jun Li
  3. Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA

    • Wei-Li Li,
    • Zachary A. Piazza &
    • Lai-Sheng Wang
  4. Department of Chemistry, Fudan University, Shanghai 200433, China

    • Guang-Feng Wei &
    • Zhi-Pan Liu


H-J.Z., S-D.L., J.L. and L-S.W. designed the project. H-J.Z. and W-L.L. carried out the experiments. Q.C., H.B., W-J.T., H-G.L., Y-B.W. and Y-W.M. constructed the guess structures and did the electronic structure calculations and spectral simulations. G-F.W., Z-P.L. and Y-F.Z. did the SSW and BH structural searches independently. H-S.H. performed the CCSD calculations. H-J.Z., J.L., S-D.L. and L-S.W. analysed the data and wrote the paper. All authors discussed the results and made comments and edits to the manuscript.

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