Aromaticity/Antiaromaticity in “Bare” and “Ligand-Stabilized” Rings of Metal Atoms

Tsipis, Constantinos A.

doi:10.1007/978-3-642-05243-9_7

Cited by 19 publications

(19 citation statements)

References 170 publications

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“…A closer look, however, reveals that the CIRCO pattern in 2 (and in part in 3 ), and in fact the whole aromatic pattern, is of σ type, which is often encountered in metallic compounds . Therefore, we can assume that σ type aromaticity, contrary to π type, can be associated (at least in periodic graphene dots and antidots) with higher (not lower) conductivity.…”

Section: Resultsmentioning

confidence: 87%

“…27 Therefore, we can assume that σ type aromaticity, contrary to π type, can be associated (at least in periodic graphene dots and antidots) with higher (not lower) conductivity.…”

Section: Resultsmentioning

confidence: 99%

“…For σ aromaticity (commonly encounter in metallic compounds 27 ), in general the opposite would be expected, in particular for extended periodical structures.…”

Section: Discussionmentioning

confidence: 98%

“…Furthermore, on the basis of our calculations:

We verify and generalize the experimental findings that aromaticity and conductivity vary in an opposite way (the higher the aromaticity of the “molecule”, the lower its conductivity and vice versa).

However, this is true only for π aromaticity. For σ aromaticity (commonly encounter in metallic compounds 27 ), in general the opposite would be expected, in particular for extended periodical structures.

We predict and verify numerically that conductivity in rectangular (nano)graphene samples with both armchair and zigzag edges is anisotropic; with the conductivity along the direction connecting the zigzag edges (in other words, perpendicular to the zigzag edges) being much higher (sometimes by 1 order of magnitude) compared to the direction connecting the armchair edges, which, as we have shown earlier, are much more aromatic compared to (the region around) the zigzag edges.It is shown that both mobility and polarizability contribute to this anisotropy.GNRs of proper length, which are Clar aromatic (or else “more aromatic”) have comparatively lower values of conductivity, although their LUMO–HOMO gaps could be lower, in relation to non-Clar GNRs of the same length. Thus, the “conductivity criterion” presented here could be much safer compared to LUMO–HOMO gap comparisons.…”

Section: Discussionmentioning

confidence: 99%

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Interrelation of Aromaticity and Conductivity of Graphene Dots/Antidots and Related Nanostructures

Zdetsis

Economou

2016

J. Phys. Chem. C

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It is illustrated and computationally verified by ab initio density functional theory and simple but powerful order-of-magnitude arguments, based on deformation energy ΔEdef in relation to the uncertainty principle, that the conductivity and aromaticity of graphene and graphene-based structures, such as graphene dots, antidots, and nanoribbons, are negatively interrelated for π aromatic structures, in agreement with recent experimental data. However, for σ aromaticity, the interrelation could be positive, especially for extended periodic structures. We predict that the conductivity of rectangular graphene dots and antidots, is anisotropic with much larger magnitude along the direction perpendicular to the zigzag edges, compared to the conductivity in direction parallel to them. The same is true for the polarizability and electron mobility. This is directly connected with the much higher aromaticity around the armchair edges compared to the aromaticity near the zigzag edges. Furthermore, contrary to what would be expected on the basis of simple arguments for defect states, we predict that antidot patterning could significantly improve the conductivity (sometimes by 1 order of magnitude) in one or both directions, depending on their number, arrangement, and passivation. For narrow atomically precise armchair nanoribbons (AGNRs) of finite length, both conductivity and energy gaps are dominated by lateral and longitudinal quantum confinement, which decrease with increasing length (for a given width), leading to a peculiar behavior of monotonically increasing “maximum conductivity” as the band gaps monotonically decrease. The electron distribution at the band edges of the AGNRs, in agreement with recent experimental data are well-localized at the zigzag edges. Using the concept of gap-determining LUMO–HOMO frontier states to avoid HOMOs and LUMOs localized at the zigzag edges, we can predict with very high accuracy the recently measured band gaps of AGNRs of widths N = 7 and N = 13. Both the smallest (10–3–10–4) and the largest (a few 2) calculated values of conductance and conductivity for the smaller structures and the larger nanographenes, respectively, are in full accord with the corresponding experimental values of single-molecule junction conductance and the measured minimum conductivity of graphene at 1.6 K.

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Section: Resultsmentioning

confidence: 87%

“…27 Therefore, we can assume that σ type aromaticity, contrary to π type, can be associated (at least in periodic graphene dots and antidots) with higher (not lower) conductivity.…”

Section: Resultsmentioning

confidence: 99%

“…For σ aromaticity (commonly encounter in metallic compounds 27 ), in general the opposite would be expected, in particular for extended periodical structures.…”

Section: Discussionmentioning

confidence: 98%

“…Furthermore, on the basis of our calculations:

Section: Discussionmentioning

confidence: 99%

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Interrelation of Aromaticity and Conductivity of Graphene Dots/Antidots and Related Nanostructures

Zdetsis

Economou

2016

J. Phys. Chem. C

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“…An electronic effect from Z 5 -coordinating ligands can thus be considered in the CoS 3 system, similar to the case of ligand-stabilized clusters. 51 Conjugation of r, p, and lone pairs Aromaticity can arise not only from p electrons, but also from conjugation brought about by hybridization of p electrons, s electrons, and lone pairs. A group headed by Rzepa and Scheschkewitz recently reported the synthesis, isolation, and characterization of a chair-shaped tricyclic isomer of hexasilabenzene (Si 6 H 6 ), by using bulky 2,4,6-triisopropylphenyl groups as steric protecting groups, to find the isomer that contains an aromatic Si 4 unit (Fig.…”

Section: +mentioning

confidence: 99%

The chemistry of four-membered aromatics

Maruyama

2012

Chem. Commun.

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This article provides an overview on the aromatic systems of four-membered rings. These aromatic four-membered ring systems are rather exotic because of a poor correspondence between the Hückel rule and the structure of four-membered rings. Consequently, such aromatics are generally dications or dianions, to form 2π or 6π electron systems respectively. Alternatively, the use of open-shell structures or empty d-orbitals of transition metal atoms could give neutral aromatic four-membered ring systems. This paper summarizes the four-membered aromatic compounds reported to date and describes the various methods for evaluating their aromaticity.

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σ‐, π‐, δ‐, and ϕ‐Aromaticity

2022

Aromaticity and Antiaromaticity

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Aromaticity/Antiaromaticity in “Bare” and “Ligand-Stabilized” Rings of Metal Atoms

Cited by 19 publications

References 170 publications

Interrelation of Aromaticity and Conductivity of Graphene Dots/Antidots and Related Nanostructures

Interrelation of Aromaticity and Conductivity of Graphene Dots/Antidots and Related Nanostructures

The chemistry of four-membered aromatics

σ‐, π‐, δ‐, and ϕ‐Aromaticity

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