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 94 publications

(128 citation statements)

References 56 publications

Supporting

Mentioning

108

Contrasting

Order By: Relevance

“…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

View full text Add to dashboard Cite

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.

show abstract

Section: Concluding Summarycontrasting

confidence: 93%

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

Weinhold

2022

Molecules

View full text Add to dashboard Cite

show abstract

“…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

View full text Add to dashboard Cite

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.

show abstract

“…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

View full text Add to dashboard Cite

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.

show abstract

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

Cited by 94 publications

References 56 publications

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

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

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

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

Contact Info

Product

Resources

About