Boron displays many unusual structural and bonding properties due to its electron deficiency. Here we show that a boron atom in a boron monoxide cluster (B 9 O − ) exhibits transition-metal-like properties. Temperature-dependent photoelectron spectroscopy provided evidence of the existence of two isomers for B 9 O − : the main isomer has an adiabatic detachment energy (ADE) of 4.19 eV and a higher energy isomer with an ADE of 3.59 eV. The global minimum of B 9 O − is found surprisingly to be an umbrella-like structure ( C 6v , 1 A 1 ) and its simulated spectrum agrees well with that of the main isomer observed. A low-lying isomer ( C s , 1 A′) consisting of a BO unit bonded to a disk-like B 8 cluster agrees well with the 3.59 eV ADE species. The unexpected umbrella-like global minimum of B 9 O − can be viewed as a central boron atom coordinated by a η 7 -B 7 ligand on one side and a BO ligand on the other side, [(η 7 -B 7 )-B-BO] − . The central B atom is found to share its valence electrons with the B 7 unit to fulfill double aromaticity, similar to that in half-sandwich [(η 7 -B 7 )-Zn-CO] − or [(η 7 -B 7 )-Fe(CO) 3 ] − transition-metal complexes. The ability of boron to form a half-sandwich complex with an aromatic ligand, a prototypical property of transition metals, brings out new metallomimetic properties of boron.
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PrB 7 − : A Praseodymium‐Doped Boron Cluster with a Pr II Center Coordinated by a Doubly Aromatic Planar η 7 ‐B 7 3− Ligand
The structure and bonding of a Pr‐doped boron cluster (PrB7−) are investigated using photoelectron spectroscopy and quantum chemistry. The adiabatic electron detachment energy of PrB7−is found to be low [1.47(8) eV]. A large energy gap is observed between the first and second detachment features, indicating a highly stable neutral PrB7. Global minimum searches and comparison between experiment and theory show that PrB7−has a half‐sandwich structure with C6vsymmetry. Chemical bonding analyses show that PrB7−can be viewed as a PrII[η7‐B73−] complex with three unpaired electrons, corresponding to a Pr (4f26s1) open‐shell configuration. Upon detachment of the 6s electron, the neutral PrB7cluster is a highly stable PrIII[η7‐B73−] complex with Pr in its favorite +3 oxidation state. The B73−ligand is found to be highly stable and doubly aromatic with six delocalized π and six delocalized σ electrons and should exist for a series of lanthanide MIII[η7‐B73−] complexes.
more » « less- NSF-PAR ID:
- 10034846
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie
- Volume:
- 129
- Issue:
- 24
- ISSN:
- 0044-8249
- Page Range / eLocation ID:
- p. 7020-7024
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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