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Open AccessArticle

σ-Holes vs. Buildups of Electronic Density on the Extensions of Bonds to Halogen Atoms

Department of Chemistry, University of New Orleans, New Orleans, LA 70148, USA
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Inorganics 2019, 7(6), 71; https://doi.org/10.3390/inorganics7060071
Received: 13 May 2019 / Revised: 28 May 2019 / Accepted: 31 May 2019 / Published: 6 June 2019
(This article belongs to the Special Issue Halogen Bonding: Fundamentals and Applications)
Our discussion focuses upon three possible features that a bonded halogen atom may exhibit on its outer side, on the extension of the bond. These are (1) a region of lower electronic density (a σ-hole) accompanied by a positive electrostatic potential with a local maximum, (2) a region of lower electronic density (a σ-hole) accompanied by a negative electrostatic potential that also has a local maximum, and (3) a buildup of electronic density accompanied by a negative electrostatic potential that has a local minimum. In the last case, there is no σ-hole. We show that for diatomic halides and halogen-substituted hydrides, the signs and magnitudes of these maxima and minima can be expressed quite well in terms of the differences in the electronegativities of the halogen atoms and their bonding partners, and the polarizabilities of both. We suggest that the buildup of electronic density and absence of a σ-hole on the extension of the bond to the halogen may be an operational indication of ionicity. View Full-Text
Keywords: halogen bonding; σ-holes; positive and negative electrostatic potentials; electronic densities; ionicity halogen bonding; σ-holes; positive and negative electrostatic potentials; electronic densities; ionicity
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Politzer, P.; Murray, J.S. σ-Holes vs. Buildups of Electronic Density on the Extensions of Bonds to Halogen Atoms. Inorganics 2019, 7, 71.

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