This content will become publicly available on April 20, 2023
- Award ID(s):
- 2053541
- Publication Date:
- NSF-PAR ID:
- 10319799
- Journal Name:
- Annual Review of Physical Chemistry
- Volume:
- 73
- Issue:
- 1
- ISSN:
- 0066-426X
- Sponsoring Org:
- National Science Foundation
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Because of their interesting structures and bonding and potentials as motifs for new nanomaterials, size-selected boron clusters have received tremendous interest in recent years. In particular, boron cluster anions (B n − ) have allowed systematic joint photoelectron spectroscopy and theoretical studies, revealing predominantly two-dimensional structures. The discovery of the planar B 36 cluster with a central hexagonal vacancy provided the first experimental evidence of the viability of 2D borons, giving rise to the concept of borophene. The finding of the B 40 cage cluster unveiled the existence of fullerene-like boron clusters (borospherenes). Metal-doping can significantly extend the structural and bonding repertoire of boron clusters. Main-group metals interact with boron through s/p orbitals, resulting in either half-sandwich-type structures or substitutional structures. Transition metals are more versatile in bonding with boron, forming a variety of structures including half-sandwich structures, metal-centered boron rings, and metal-centered boron drums. Transition metal atoms have also been found to be able to be doped into the plane of 2D boron clusters, suggesting the possibility of metalloborophenes. Early studies of di-metal-doped boron clusters focused on gold, revealing ladder-like boron structures with terminal gold atoms. Recent observations of highly symmetric Ta 2 B 6 − and Ln 2more »
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Transition-metal-centered monocyclic boron wheel clusters (M©Bnq) represent a family of interesting borometallic compounds with double aromaticity. A variety of early and late transition metal atoms have been found to form such structures with high symmetries and various Bn ring sizes. Here we report a combined photoelectron spectroscopy and quantum chemistry theoretical study of two M©Bn– clusters from the middle of the transition metal series: Re©B8– and Re©B9–. Global minimum structure searches reveal that ReB8– adopts a pseudo-C8v structure, while ReB9– is a perfect-planar D9h molecular wheel. Chemical bonding analyses show that both clusters exhibit and double aromaticity and obey the electronic design principle for metal-centered borometallic molecular wheels. The central Re atom are found to possess unusually low oxidation states of +I in Re©B8– and +II in Re©B9–, i.e. the Re atom behaves similarly to late transition-metal elements (Ru, Fe, Co, Rh, Ir) in the M©Bn– molecular wheels. These two clusters become new members of the family of transition-metal-centered monocyclic borometallic molecular wheels, which may be viable for chemical syntheses with appropriate ligands.
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Abstract Despite its electron deficiency, boron can form multiple bonds with a variety of elements. However, multiple bonds between boron and main-group metal elements are relatively rare. Here we report the observation of boron-lead multiple bonds in PbB2O–and PbB3O2–, which are produced and characterized in a cluster beam. PbB2O–is found to have an open-shell linear structure, in which the bond order of B☱Pb is 2.5, while the closed-shell [Pb≡B–B≡O]2–contains a B≡Pb triple bond. PbB3O2–is shown to have a Y-shaped structure with a terminal B = Pb double bond coordinated by two boronyl ligands. Comparison between [Pb≡B–B≡O]2–/[Pb=B(B≡O)2]–and the isoelectronic [Pb≡B–C≡O]–/[Pb=B(C≡O)2]+carbonyl counterparts further reveals transition-metal-like behaviors for the central B atoms. Additional theoretical studies show that Ge and Sn can form similar boron species as Pb, suggesting the possibilities to synthesize new compounds containing multiple boron bonds with heavy group-14 elements.
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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 tomore »
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