Noncovalent Bonds through Sigma and Pi-Hole Located on the Same Molecule. Guiding Principles and Comparisons

Zierkiewicz, Wiktor; Michalczyk, Mariusz; Scheiner, Steve

doi:10.3390/molecules26061740

Cited by 46 publications

(46 citation statements)

References 158 publications

(230 reference statements)

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“…Although not as extensive as the research centering on σ-hole bonds, there has been substantial coverage of their π-hole cousins as well, particularly in the past few years. ,,− This work has covered the full gamut of central atoms, from aerogen to pnicogen to triel bonds. In summary, it has been learned that π-hole bonds can be quite strong, competitive with their σ-hole bond sisters, and even stronger in some circumstances.…”

Section: Introductionmentioning

confidence: 99%

Dissection of the Origin of π-Holes and the Noncovalent Bonds in Which They Engage

Scheiner

2021

J. Phys. Chem. A

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Accompanying the rapidly growing list of σ-hole bonds has come the acknowledgment of parallel sorts of noncovalent bonds which owe their stability in large part to a deficiency of electron density in the area above the molecular plane, known as a π-hole. The origins of these π-holes are probed for a wide series of molecules, comprising halogen, chalcogen, pnicogen, tetrel, aerogen, and spodium bonds. Much like in the case of their σ-hole counterparts, formation of the internal covalent π-bond in the Lewis acid molecule pulls density toward the bond midpoint and away from its extremities. This depletion of density above the central atom is amplified by an electron-withdrawing substituent. At the same time, the amplitude of the π*-orbital is enhanced in the region of the density-depleted π-hole, facilitating a better overlap with the nucleophile’s lone pair orbital and a stabilizing n → π* charge transfer. The presence of lone pairs on the central atom acts to attenuate the π-hole and shift its position somewhat, resulting in an overall weakening of the π-hole bond. There is a tendency for π-hole bonds to include a higher fraction of induction energy than σ-bonds with proportionately smaller electrostatic and dispersion components, but this distinction is less a product of the σ- or π-character and more a function of the overall bond strength.

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Section: Introductionmentioning

confidence: 99%

Dissection of the Origin of π-Holes and the Noncovalent Bonds in Which They Engage

Scheiner

2021

J. Phys. Chem. A

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“…The types of holes that emerged from these studies range from σ to π to δ ( Angarov and Kozuch, 2018 ). Simultaneously, the names of bonds associated with these “holes” exploded up to 8 by the last count ( Zierkiewicz et al, 2021 ). The “hole” properties such as the spatial extent of the positive region ( Kolář et al, 2015 ), the value of the maximal electrostatic potential, V smax , at a certain threshold density ( Politzer et al, 2013 ), and the extent of the hole’s “polar flattening” ( Sedlak et al, 2015 ) have been correlated with the bonding strength of a complex.Simultaneously, there were claims that only the density and its associated electrostatics represent “phenomena” and all the other computable and physically interpretable effects represent “unicorns” ( Politzer et al, 2015 ).…”

Section: Resultsmentioning

confidence: 99%

“…The weak donor–acceptor interactions encompass a wide swath of noncovalent interactions from noble-gas molecule to halogen-bonded to metalophilic. New types are being discovered by examinations of crystal structures ( Ramasubbu et al, 1986 ; Bauzá et al, 2013 ; Saha and Desiraju, 2017 ; Saha et al, 2018 ) while new names are added to the lexicons [for the latest list see ( Zierkiewicz et al, 2021 )]. One common feature of these interactions is the presence of broadly defined Lewis acid as an electron acceptor from an electron-rich Lewis base.…”

Section: Introductionmentioning

confidence: 99%

Reassessing the Role of σ Holes in Noncovalent Interactions: It is Pauli Repulsion that Counts

Szczȩśniak

Chałasiński

2022

Front. Chem.

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A number of prototypical weak electron donor–electron acceptor complexes are investigated by the Symmetry Adapted Perturbation Theory, some of which belong to novel classes of weak bonds such as halogen and chalcogen bonds. Also included are complexes involving strong Lewis acids such as BeO and AuF. The common view in the literature is to associate these novel bonds with a variety of “holes”, σ, π, δ, or positive areas in their electrostatic potential maps. The presumption is that these positive areas of the electrostatic potential are indicative of the electrostatic nature of these noncovalent bonds. The electrostatic view extends to the explanations of the directionality of approaches between the subsystems forming these bonds. This work demonstrates that one common feature of these electrostatic potential “holes” is the local depletion of electron density of which the best detector is the first-order Pauli repulsion. The minimization of this repulsion determines the bond directionality and its relative angular rigidity. In relatively strong complexes of BeO with rare gases, where BeO shows a clear cavity in electron density—an ultimate “σ hole”—the electrostatic effect does not control the bending potential—the exchange repulsion does. In halogen bonds, the halogen atom is nonspherical, displaying an axial “σ hole” in its electrostatic potential. However, in no examined case, from rare gas acting as an electron donor to a polar donor to an anionic donor, is the electrostatic energy responsible for the directionality of the halogen bond. In fact, it is not even maximized in the direction of the σ hole in N2-ClF and NH3-ClF. Yet, in all the cases, the exchange repulsion is minimized in the direction of the σ hole. The minimized exchange repulsion associated with the subtle and less subtle depletions of the electron density occur on the nodal planes or on the intersections thereof in the highest occupied molecular orbitals of Lewis acids, provided that the systems are closed-shell. The role of nodal planes in covalent and coordinate covalent bonds is well recognized. This work points to their similarly equal importance in certain types of donor–acceptor noncovalent interactions.

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“…In addition, the electron‐withdrawing O will enhance the lobe of the π* antibonding orbital that lies above the C atom, thereby facilitating charge transfer from the nucleophile in a direct parallel with σ‐hole bonding. Although the majority of the earlier studies of these sorts of noncovalent bonds were focused on σ‐hole bonds, there is a growing emphasis to better explore their π‐hole analogues 3,7,12,33–43 . While this work is continuing, it is important to stress here, that there are strong indications that π‐hole bonds are not necessarily weaker than their σ‐hole counterparts, and can indeed be stronger in numerous instances.…”

Section: Introductionmentioning

confidence: 97%

Maximal occupation by bases of π‐hole bands surrounding linear molecules

Scheiner

2021

J Comput Chem

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Linear molecules such as CO2 contain a positive π‐hole ring that surrounds C on the molecule's equator. Quantum calculations examine the question as to how many bases can simultaneously bind to this ring. Linear molecules examined are TO2, where T = C, Si, Ge, Sn; bases are NCH and NH3. CO2 engages in the weakest of the tetrel bonds, and can bind up to three NCH and two NH3. Unlike σ‐hole tetrel bonds, Si forms the strongest tetrel bonds, with interaction energies as high as 43 kcal/mol with NH3. But like GeO2, SiO2 can sustain only two bases in its equatorial ring. The π‐hole ring of SnO2 can engage in up to four tetrel bonds with either NCH or NH3, even though these bonds are weaker than those with GeO2 or SiO2. As all of these complexes cast TO2 in the role of multiple electron acceptor, the resulting negative cooperativity makes each successive bond weaker than its predecessor as bases are added, as well as reducing the magnitude of the central molecule's π‐hole.

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Noncovalent Bonds through Sigma and Pi-Hole Located on the Same Molecule. Guiding Principles and Comparisons

Cited by 46 publications

References 158 publications

Dissection of the Origin of π-Holes and the Noncovalent Bonds in Which They Engage

Dissection of the Origin of π-Holes and the Noncovalent Bonds in Which They Engage

Reassessing the Role of σ Holes in Noncovalent Interactions: It is Pauli Repulsion that Counts

Maximal occupation by bases of π‐hole bands surrounding linear molecules

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