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Despite the importance of bulk lanthanide borides, nanoclusters of lanthanide and boron have rarely been investigated. Here we show that lanthanide–boron binary clusters, La 2 B x − , can form a new class of inverse-sandwich complexes, [Ln(η x -B x )Ln] − ( x = 7–9). Joint experimental and theoretical studies reveal that the monocyclic B x rings in the inverse sandwiches display similar bonding, consisting of three delocalized σ and three delocalized π bonds. Such monocyclic boron rings do not exist for bare boron clusters, but they are stabilized by the sandwiching lanthanide atoms. An electron counting rule is proposed to predict the sizes of the B x ring that can form stable inverse sandwiches. A unique (d-p)δ bond is found to play important roles in the stability of all three inverse-sandwich complexes.
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Observation of the Smallest Three‐Dimensional Neutral Boron Cluster
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 B9cluster using threshold photoionization with a tunable vacuum ultraviolet free electron laser. The ionization potential of B9is measured to be 8.45±0.02 eV and it is found to have a heptagonal bipyramidD7hstructure, 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 B7ring and between the B7ring and the capping atoms. Photoionization of B9breaks the single‐electron B‐B bond of the capping atoms, which undergo off‐axis distortion to enhance interactions with the B7ring in the singlet ground state of B9+. The single‐electron B‐B bond of the capping atoms appears to be crucial in stabilizing theD7hstructure 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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- Award ID(s):
- 2403841
- PAR ID:
- 10573064
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 64
- Issue:
- 8
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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