The ground singlet and low-lying triplet electronic states of B3+

“…They initially postulated the three‐dimensional structures for boron clusters. Consequent quantum chemical calculations32–62 have shown that boron clusters prefer planar or quasi‐planar structures. However, these computational predictions were not verified experimentally.…”

Section: Introductionmentioning

confidence: 99%

Comprehensive analysis of chemical bonding in boron clusters

2006

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We present a comprehensive analysis of chemical bonding in pure boron clusters. It is now established in joint experimental and theoretical studies that pure boron clusters are planar or quasi-planar at least up to twenty atoms. Their planarity or quasi-planarity was usually discussed in terms of -delocalization or -aromaticity. In the current article, we demonstrated that one cannot ignore -electrons and that the presence of two-center two-electron (2cÀ À2e) peripheral BÀ ÀB bonds together with the globally delocalized -electrons must be taken into consideration when the shape of pure boron cluster is discussed. The global aromaticity (or global antiaromaticity) can be assigned on the basis of the 4n þ 2 (or 4n) electron counting rule for either -or -electrons in the planar structures. We showed that pure boron clusters could have double (-and -) ,-antiaromatic and -aromatic and B 14 , -aromatic and -antiaromatic). Appropriate geometric fit is also an essential factor, which determines the shape of the most stable structures. In all the boron clusters considered here, the peripheral atoms form planar cycles. Peripheral 2cÀ À2e BÀ ÀB bonds are built up from s to p hybrid atomic orbitals and this enforces the planarity of the cycle. If the given number of central atoms (1, 2, 3, or 4) can perfectly fit the central cavity then the overall structure is planar. Otherwise, central atoms come out of the plane of the cycle and the overall structure is quasi-planar.

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“…In 1988, Anderson et al observed the mass distribution of B n + in the range n = 1−20 generated by laser ablation of isotopically pure boron. − They postulated the three-dimensional structures for these elemental boron clusters . Properties and stability of boron clusters have since been of special interest to theoretical and computational chemists. − Molecular orbital (MO) calculations were repeatedly carried out to determine the nuclear arrangements of boron clusters. − In 1994, Boustani found that for many boron clusters the planar or quasi-planar nuclear arrangement is consistently more stable than any t...…”

Section: Introductionmentioning

confidence: 99%

Aromaticity of Planar Boron Clusters Confirmed

2005

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Low-energy boron clusters are characterized by two-dimensional geometry. Aromaticity of these planar boron clusters was established in terms of topological resonance energy (TRE). All planar boron clusters were found to be highly aromatic with large positive TREs even if they have 4n pi-electrons. Aromaticity must therefore be the origin of unusual planar or quasi-planar geometry. Thus, the aromaticity concept is as useful in boron chemistry as it is in general organic chemistry. It is evident that the Hückel 4n + 2 rule of aromaticity should not be applied to such polycyclic pi-systems. Some of the boron clusters are in the triplet electronic state to attain higher aromaticity. Multivalency and electron deficiency of boron atoms are responsible for lowering the energies of low-lying pi molecular orbitals and then for enhancing aromaticity. For polycyclic pi-systems, paratropicity does not always indicate antiaromaticity.

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The ground singlet and low-lying triplet electronic states of B3+

Cited by 7 publications

References 15 publications

Ab initio geometries, electronic structures of MgB2 molecule

Ab initio geometries, electronic structures of MgB2 molecule

Comprehensive analysis of chemical bonding in boron clusters

Aromaticity of Planar Boron Clusters Confirmed

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