Real-space imaging of anisotropic charge of σ-hole by means of Kelvin probe force microscopy

Mallada, Benjamín; Gallardo, Aurelio; Lamanec, Maximilián; Torre, Bruno de la; Špirko, V.; Hobza, Pavel; Jelı́nek, Pavel

doi:10.1126/science.abk1479

Cited by 104 publications

(128 citation statements)

References 56 publications

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“…Our results do not discount the anisotropies of atomic charge distribution underlying calculated [17][18][19][20][21][22][23][24][25][26][27][28][29] or measured [92] variations of the associated electrostatic potential around isolated monomers. However, they demonstrate that such (expected!)…”

Section: Concluding Summarycontrasting

confidence: 93%

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

Weinhold

2022

Molecules

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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) nD-π*AX interactions that are fully analogous to the nD-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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Section: Concluding Summarycontrasting

confidence: 93%

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

Weinhold

2022

Molecules

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“…When X = Br and I, a halogen-bonded complex [CH 3 –X∙∙∙M] − can be formed with a linear C-X-M bond, it is known that when halogen atom, especially I and Br, binds to an electron withdrawing group, such as CF 3 or CH 3 in our case, a σ -hole that carries positive charge appears on the other side of halogen atom along the axis of the C–X bond. Although theory predicted the existence of the σ -hole in 2007 by Politzer’s group [ 54 ] and strategies were developed to stabilize anions with halogen bonding [ 55 ], the σ -hole has been observed by experiments in 4BrPhM molecules only recently [ 56 ]. As a result, the σ -hole attracts negatively charged species to form a halogen bond.…”

Section: Resultsmentioning

confidence: 99%

Computational Studies of Coinage Metal Anion M− + CH3X (X = F, Cl, Br, I) Reactions in Gas Phase

Wang

Ying

et al. 2022

Molecules

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We characterized the stationary points along the nucleophilic substitution (SN2), oxidative insertion (OI), halogen abstraction (XA), and proton transfer (PT) product channels of M− + CH3X (M = Cu, Ag, Au; X = F, Cl, Br, I) reactions using the CCSD(T)/aug-cc-pVTZ level of theory. In general, the reaction energies follow the order of PT > XA > SN2 > OI. The OI channel that results in oxidative insertion complex [CH3–M–X]− is most exothermic, and can be formed through a front-side attack of M on the C-X bond via a high transition state OxTS or through a SN2-mediated halogen rearrangement path via a much lower transition state invTS. The order of OxTS > invTS is inverted when changing M− to Pd, a d10 metal, because the symmetry of their HOMO orbital is different. The back-side attack SN2 pathway proceeds via typical Walden-inversion transition state that connects to pre- and post-reaction complexes. For X = Cl/Br/I, the invSN2-TS’s are, in general, submerged. The shape of this M− + CH3X SN2 PES is flatter as compared to that of a main-group base like F− + CH3X, whose PES has a double-well shape. When X = Br/I, a linear halogen-bonded complex [CH3−X∙··M]− can be formed as an intermediate upon the front-side attachment of M on the halogen atom X, and it either dissociates to CH3 + MX− through halogen abstraction or bends the C-X-M angle to continue the back-side SN2 path. Natural bond orbital analysis shows a polar covalent M−X bond is formed within oxidative insertion complex [CH3–M–X]−, whereas a noncovalent M–X halogen-bond interaction exists for the [CH3–X∙··M]− complex. This work explores competing channels of the M− + CH3X reaction in the gas phase and the potential energy surface is useful in understanding the dynamic behavior of the title and analogous reactions.

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“…This σ-hole can attract the negative region of an approaching nucleophile, its lone pair for example. The σ-hole was originally conceived within the context of polar flattening of the electron density from x-ray diffraction work, [25][26][27][28] and has recently been visualized [29] by Kelvin probe force microscopy at the appropriate position on a halogen atom. This Coulombic force is supplemented by a stabilizing charge transfer from the nucleophile's lone pair into the σ*(RÀ X) antibonding orbital.…”

Section: Introductionmentioning

confidence: 99%

Influence of Substituents in the Benzene Ring on the Halogen Bond of Iodobenzene with Ammonia

Scheiner

Hunter

2022

ChemPhysChem

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The effects on the CÀ I••N halogen bond between iodobenzene and NH 3 of placing various substituents on the phenyl ring are monitored by quantum calculations. Substituents R = N(CH 3 ) 2 , NH 2 , CH 3 , OCH 3 , COCH 3 , Cl, F, COH, CN, and NO 2 were each placed ortho, meta, and para to the I. The depth of the σ-hole on I is deepened as R becomes more electron-withdrawing which is reflected in a strengthening of the halogen bond, which varied between 3.3 and 5.5 kcal mol À 1 . In most cases, the ortho placement yields the largest perturbation, followed by meta and then para, but this trend is not universal. Parallel to these substituent effects is a progressive lengthening of the covalent CÀ I bond. Formation of the halogen bond reduces the NMR chemical shielding of all three nuclei directly involved in the CÀ I••N interaction. The deshielding of the electron donor N is most closely correlated with the strength of the bond, as is the coupling constant between I and N, so both have potential use as spectroscopic measures of halogen bond strength.

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Real-space imaging of anisotropic charge of σ-hole by means of Kelvin probe force microscopy

Cited by 104 publications

References 56 publications

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

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

Computational Studies of Coinage Metal Anion M− + CH3X (X = F, Cl, Br, I) Reactions in Gas Phase

Influence of Substituents in the Benzene Ring on the Halogen Bond of Iodobenzene with Ammonia

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