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Anti-Electrostatic Pi-Hole Bonding: How Covalency Conquers Coulombics

Intermolecular bonding attraction at π-bonded centers is often described as “electrostatically driven” and given quasi-classical rationalization in terms of a “pi hole” depletion region in the electrostatic potential. However, we demonstrate here that such bonding attraction also occurs between clos...

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Autor principal: Weinhold, Frank
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2022
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8780338/
https://www.ncbi.nlm.nih.gov/pubmed/35056689
http://dx.doi.org/10.3390/molecules27020377
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author Weinhold, Frank
author_facet Weinhold, Frank
author_sort Weinhold, Frank
collection PubMed
description Intermolecular bonding attraction at π-bonded centers is often described as “electrostatically driven” and given quasi-classical rationalization in terms of a “pi hole” depletion region in the electrostatic potential. However, we demonstrate here that such bonding attraction also occurs between closed-shell ions of like charge, thereby yielding locally stable complexes that sharply violate classical electrostatic expectations. Standard DFT and MP2 computational methods are employed to investigate complexation of simple pi-bonded diatomic anions (BO(−), CN(−)) with simple atomic anions (H(−), F(−)) or with one another. Such “anti-electrostatic” anion–anion attractions are shown to lead to robust metastable binding wells (ranging up to 20–30 kcal/mol at DFT level, or still deeper at dynamically correlated MP2 level) that are shielded by broad predissociation barriers (ranging up to 1.5 Å width) from long-range ionic dissociation. Like-charge attraction at pi-centers thereby provides additional evidence for the dominance of 3-center/4-electron (3c/4e) n(D)-π*(AX) interactions that are fully analogous to the n(D)-σ*(AH) interactions of H-bonding. Using standard keyword options of natural bond orbital (NBO) analysis, we demonstrate that both n-σ* (sigma hole) and n-π* (pi hole) interactions represent simple variants of the essential resonance-type donor-acceptor (Bürgi–Dunitz-type) attraction that apparently underlies all intermolecular association phenomena of chemical interest. We further demonstrate that “deletion” of such π*-based donor-acceptor interaction obliterates the characteristic Bürgi–Dunitz signatures of pi-hole interactions, thereby establishing the unique cause/effect relationship to short-range covalency (“charge transfer”) rather than envisioned Coulombic properties of unperturbed monomers.
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spelling pubmed-87803382022-01-22 Anti-Electrostatic Pi-Hole Bonding: How Covalency Conquers Coulombics Weinhold, Frank Molecules Article Intermolecular bonding attraction at π-bonded centers is often described as “electrostatically driven” and given quasi-classical rationalization in terms of a “pi hole” depletion region in the electrostatic potential. However, we demonstrate here that such bonding attraction also occurs between closed-shell ions of like charge, thereby yielding locally stable complexes that sharply violate classical electrostatic expectations. Standard DFT and MP2 computational methods are employed to investigate complexation of simple pi-bonded diatomic anions (BO(−), CN(−)) with simple atomic anions (H(−), F(−)) or with one another. Such “anti-electrostatic” anion–anion attractions are shown to lead to robust metastable binding wells (ranging up to 20–30 kcal/mol at DFT level, or still deeper at dynamically correlated MP2 level) that are shielded by broad predissociation barriers (ranging up to 1.5 Å width) from long-range ionic dissociation. Like-charge attraction at pi-centers thereby provides additional evidence for the dominance of 3-center/4-electron (3c/4e) n(D)-π*(AX) interactions that are fully analogous to the n(D)-σ*(AH) interactions of H-bonding. Using standard keyword options of natural bond orbital (NBO) analysis, we demonstrate that both n-σ* (sigma hole) and n-π* (pi hole) interactions represent simple variants of the essential resonance-type donor-acceptor (Bürgi–Dunitz-type) attraction that apparently underlies all intermolecular association phenomena of chemical interest. We further demonstrate that “deletion” of such π*-based donor-acceptor interaction obliterates the characteristic Bürgi–Dunitz signatures of pi-hole interactions, thereby establishing the unique cause/effect relationship to short-range covalency (“charge transfer”) rather than envisioned Coulombic properties of unperturbed monomers. MDPI 2022-01-07 /pmc/articles/PMC8780338/ /pubmed/35056689 http://dx.doi.org/10.3390/molecules27020377 Text en © 2022 by the author. https://creativecommons.org/licenses/by/4.0/Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Weinhold, Frank
Anti-Electrostatic Pi-Hole Bonding: How Covalency Conquers Coulombics
title Anti-Electrostatic Pi-Hole Bonding: How Covalency Conquers Coulombics
title_full Anti-Electrostatic Pi-Hole Bonding: How Covalency Conquers Coulombics
title_fullStr Anti-Electrostatic Pi-Hole Bonding: How Covalency Conquers Coulombics
title_full_unstemmed Anti-Electrostatic Pi-Hole Bonding: How Covalency Conquers Coulombics
title_short Anti-Electrostatic Pi-Hole Bonding: How Covalency Conquers Coulombics
title_sort anti-electrostatic pi-hole bonding: how covalency conquers coulombics
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8780338/
https://www.ncbi.nlm.nih.gov/pubmed/35056689
http://dx.doi.org/10.3390/molecules27020377
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