Observation of the Smallest Three-Dimensional Neutral Boron Cluster
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Updated: Jun 2, 2025

Spatial Separation of Molecular Conformers and Clusters
Published on: January 9, 2014
Cong-Qiao Xu1, Tiantong Wang2, Chong Wang2,3,4
1Department of Chemistry and Guangdong Provincial Key Laboratory of Catalytic Chemistry, Southern University of Science and Technology, Shenzhen 518055, China.
Abstract:
Despite major progress in the investigation of boron cluster anions, direct experimental study of neutral boron clusters remains a significant challenge because of the difficulty in size selection. Here we report a size-specific study of the neutral B9 cluster using threshold photoionization with a tunable vacuum ultraviolet free electron laser. The ionization potential of B9 is measured to be 8.45±0.02 eV and it is found to have a heptagonal bipyramid D7h structure, quite different from the planar molecular wheel of the B9 - anionic cluster. Chemical bonding analyses reveal superior stability of the bipyramidal structure arising from delocalized σ and π bonding interactions within the B7 ring and between the B7 ring and the capping atoms. Photoionization of B9 breaks the single-electron B-B bond of the capping atoms, which undergo off-axis distortion to enhance interactions with the B7 ring in the singlet ground state of B9 +. The single-electron B-B bond of the capping atoms appears to be crucial in stabilizing the D7h structure of B9. This work opens avenues for direct size-dependent experimental studies of a large variety of neutral boron clusters to explore the stepwise development of network structures.
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