Astatine Facing Janus: Halogen Bonding vs. Charge-Shift Bonding

The nature of halogen-bond interactions was scrutinized from the perspective of astatine, potentially the strongest halogen-bond donor atom. In addition to its remarkable electronic properties (e.g., its higher aromaticity compared to benzene), C6At6 can be involved as a halogen-bond donor and acceptor. Two-component relativistic calculations and quantum chemical topology analyses were performed on C6At6 and its complexes as well as on their iodinated analogues for comparative purposes. The relativistic spin–orbit interaction was used as a tool to disclose the bonding patterns and the mechanisms that contribute to halogen-bond interactions. Despite the stronger polarizability of astatine, halogen bonds formed by C6At6 can be comparable or weaker than those of C6I6. This unexpected finding comes from the charge-shift bonding character of the C–At bonds. Because charge-shift bonding is connected to the Pauli repulsion between the bonding σ electrons and the σ lone-pair of astatine, it weakens the astatine electrophilicity at its σ-hole (reducing the charge transfer contribution to halogen bonding). These two antinomic characters, charge-shift bonding and halogen bonding, can result in weaker At-mediated interactions than their iodinated counterparts.

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Asymmetric bifurcated halogen bonds

Physical Chemistry Chemical Physics ◽

10.1039/c4cp05532b ◽

2015 ◽

Vol 17 (9) ◽

pp. 6440-6450 ◽

Cited By ~ 40

Author(s):

Martin Novák ◽

Cina Foroutan-Nejad ◽

Radek Marek

Keyword(s):

Halogen Bond ◽

Lone Pair ◽

Relative Orientation ◽

Halogen Bonds ◽

Donor And Acceptor

Depending on the relative orientation of the halogen-bond donor and acceptor, this bifurcated interaction may be classified as ‘σ-hole – lone pair’ or ‘σ-hole – π’ bonding.

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Adenine as a Halogen Bond Acceptor: A Combined Experimental and DFT Study

Crystals ◽

10.3390/cryst9040224 ◽

2019 ◽

Vol 9 (4) ◽

pp. 224 ◽

Cited By ~ 7

Author(s):

Yannick Roselló ◽

Mónica Benito ◽

Elies Molins ◽

Miquel Barceló-Oliver ◽

Antonio Frontera

Keyword(s):

Density Functional ◽

Halogen Bond ◽

Lone Pair ◽

Halogen Bonding ◽

Density Functional Theory Calculations ◽

Functional Theory ◽

Adenine Ring ◽

Bonding Interaction ◽

Donor Ability ◽

Adenine Derivative

In this work, we report the cocrystallization of N9-ethyladenine with 1,2,4,5-tetrafluoro-3,6-diiodobenzene (TFDIB), a classical XB donor. As far as our knowledge extends, this is the first cocrystal reported to date where an adenine derivative acts as a halogen bond acceptor. In the solid state, each adenine ring forms two centrosymmetric H-bonded dimers: one using N1···HA6–N6 and the other N7···HB6–N6. Therefore, only N3 is available as a halogen bond acceptor that, indeed, establishes an N···I halogen bonding interaction with TFDIB. The H-bonded dimers and halogen bonds have been investigated via DFT (Density Functional Theory) calculations and the Bader’s Quantum Theory of Atoms In Molecules (QTAIM) method at the B3LYP/6-311+G* level of theory. The influence of H-bonding interactions on the lone pair donor ability of N3 has also been analyzed using the molecular electrostatic potential (MEP) surface calculations.

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Halogen-Bonded Guanine Base Pairs, Quartets and Ribbons

International Journal of Molecular Sciences ◽

10.3390/ijms21186571 ◽

2020 ◽

Vol 21 (18) ◽

pp. 6571

Author(s):

Nicholas J. Thornton ◽

Tanja van Mourik

Keyword(s):

Base Pair ◽

Halogen Bond ◽

Halogen Bonding ◽

Dna Bases ◽

Halogen Bonds ◽

Base Pairs ◽

Rich Diversity ◽

Different Types ◽

Guanine Base ◽

The Stability

Halogen bonding is studied in different structures consisting of halogenated guanine DNA bases, including the Hoogsteen guanine–guanine base pair, two different types of guanine ribbons (R-I and R-II) consisting of two or three monomers, and guanine quartets. In the halogenated base pairs (except the Cl-base pair, which has a very non-planar structure with no halogen bonds) and R-I ribbons (except the At trimer), the potential N-X•••O interaction is sacrificed to optimise the N-X•••N halogen bond. In the At trimer, the astatines originally bonded to N1 in the halogen bond donating guanines have moved to the adjacent O6 atom, enabling O-At•••N, N-At•••O, and N-At•••At halogen bonds. The brominated and chlorinated R-II trimers contain two N-X•••N and two N-X•••O halogen bonds, whereas in the iodinated and astatinated trimers, one of the N-X•••N halogen bonds is lost. The corresponding R-II dimers keep the same halogen bond patterns. The G-quartets display a rich diversity of symmetries and halogen bond patterns, including N-X•••N, N-X•••O, N-X•••X, O-X•••X, and O-X•••O halogen bonds (the latter two facilitated by the transfer of halogens from N1 to O6). In general, halogenation decreases the stability of the structures. However, the stability increases with the increasing atomic number of the halogen, and the At-doped R-I trimer and the three most stable At-doped quartets are more stable than their hydrogenated counterparts. Significant deviations from linearity are found for some of the halogen bonds (with halogen bond angles around 150°).

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Characterizing the interplay of Pauli repulsion, electrostatics, dispersion and charge transfer in halogen bonding with energy decomposition analysis

Physical Chemistry Chemical Physics ◽

10.1039/c7cp06959f ◽

2018 ◽

Vol 20 (2) ◽

pp. 905-915 ◽

Cited By ~ 96

Author(s):

Jonathan Thirman ◽

Elric Engelage ◽

Stefan M. Huber ◽

Martin Head-Gordon

Keyword(s):

Charge Transfer ◽

Bond Strength ◽

Halogen Bond ◽

Decomposition Analysis ◽

Halogen Bonding ◽

Energy Decomposition Analysis ◽

Energy Decomposition ◽

Pauli Repulsion

Variational energy decomposition analysis establishes charge-transfer as the origin of halogen bond strength differences that go against electrostatics.

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Study of the Halogen Bonding between Pyridine and Perfluoroalkyl Iodide in Solution Phase Using the Combination of FTIR and 19F NMR

International Journal of Spectroscopy ◽

10.1155/2013/216518 ◽

2013 ◽

Vol 2013 ◽

pp. 1-10 ◽

Cited By ~ 16

Author(s):

Briauna Hawthorne ◽

Haiyan Fan-Hagenstein ◽

Elizabeth Wood ◽

Jessica Smith ◽

Timothy Hanks

Keyword(s):

Halogen Bond ◽

Equilibrium Constants ◽

Binding Constants ◽

Halogen Bonding ◽

Blue Shift ◽

Halogen Bonds ◽

Perfluoroalkyl Iodide ◽

Solvent Dependence ◽

Dilution Experiments ◽

Stretching Vibrations

Halogen bonding between pyridine and heptafluoro-2-iodopropane (iso-C3F7I)/heptafluoro-1-iodopropane (1-C3F7I) was studied using a combination of FTIR and 19F NMR. The ring breathing vibration of pyridine underwent a blue shift upon the formation of halogen bonds with both iso-C3F7I and 1-C3F7I. The magnitudes of the shifts and the equilibrium constants for the halogen-bonded complex formation were found to depend not only on the structure of the halocarbon, but also on the solvent. The halogen bond also affected the Cα-F (C-F bond on the center carbon) bending and stretching vibrations in iso-C3F7I. These spectroscopic effects show some solvent dependence, but more importantly, they suggest the possibility of intermolecular halogen bonding among iso-C3F7I molecules. The systems were also examined by 19F NMR in various solvents (cyclohexane, hexane, chloroform, acetone, and acetonitrile). NMR dilution experiments support the existence of the intermolecular self-halogen bonding in both iso-C3F7I and 1-C3F7I. The binding constants for the pyridine/perfluoroalkyl iodide halogen bonding complexes formed in various solvents were obtained through NMR titration experiments. Quantum chemical calculations were used to support the FTIR and 19F NMR observations.

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In Situ Assessment of Intrinsic Strength of X-I⋯OA-Type Halogen Bonds in Molecular Crystals with Periodic Local Vibrational Mode Theory

Molecules ◽

10.3390/molecules25071589 ◽

2020 ◽

Vol 25 (7) ◽

pp. 1589 ◽

Cited By ~ 9

Author(s):

Yunwen Tao ◽

Yue Qiu ◽

Wenli Zou ◽

Sadisha Nanayakkara ◽

Seth Yannacone ◽

...

Keyword(s):

Bond Strength ◽

Vibrational Mode ◽

Halogen Bond ◽

Molecular Crystals ◽

Halogen Bonding ◽

Halogen Bonds ◽

Mode Theory ◽

Local Vibrational Mode ◽

Intrinsic Strength

Periodic local vibrational modes were calculated with the rev-vdW-DF2 density functional to quantify the intrinsic strength of the X-I⋯OA-type halogen bonding (X = I or Cl; OA: carbonyl, ether and N-oxide groups) in 32 model systems originating from 20 molecular crystals. We found that the halogen bonding between the donor dihalogen X-I and the wide collection of acceptor molecules OA features considerable variations of the local stretching force constants (0.1–0.8 mdyn/Å) for I⋯O halogen bonds, demonstrating its powerful tunability in bond strength. Strong correlations between bond length and local stretching force constant were observed in crystals for both the donor X-I bonds and I⋯O halogen bonds, extending for the first time the generalized Badger’s rule to crystals. It is demonstrated that the halogen atom X controlling the electrostatic attraction between the σ -hole on atom I and the acceptor atom O dominates the intrinsic strength of I⋯O halogen bonds. Different oxygen-containing acceptor molecules OA and even subtle changes induced by substituents can tweak the n → σ ∗ (X-I) charge transfer character, which is the second important factor determining the I⋯O bond strength. In addition, the presence of the second halogen bond with atom X of the donor X-I bond in crystals can substantially weaken the target I⋯O halogen bond. In summary, this study performing the in situ measurement of halogen bonding strength in crystalline structures demonstrates the vast potential of the periodic local vibrational mode theory for characterizing and understanding non-covalent interactions in materials.

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Halogen Bonding in the Complexes of Brominated Electrophiles with Chloride Anions: From a Weak Supramolecular Interaction to a Covalent Br–Cl Bond

Crystals ◽

10.3390/cryst10121075 ◽

2020 ◽

Vol 10 (12) ◽

pp. 1075

Author(s):

Cody Loy ◽

Matthias Zeller ◽

Sergiy V. Rosokha

Keyword(s):

Bond Strength ◽

Halogen Bond ◽

Covalent Bond ◽

Halogen Bonding ◽

Halogen Bonds ◽

Nucleophilic Reaction ◽

X Ray ◽

Wide Range ◽

Judicious Choice ◽

Range Variation

The wide-range variation of the strength of halogen bonds (XB) not only facilitates a variety of applications of this interaction, but it also allows examining the relation (and interconversion) between supramolecular and covalent bonding. Herein, the Br…Cl halogen bonding in a series of complexes of bromosubstituted electrophiles (R-Br) with chloride anions were examined via X-ray crystallographic and computational methods. Six co-crystals showing such bonding were prepared by evaporation of solutions of R-Br and tetra-n-propylammonium chloride or using Cl− anions released in the nucleophilic reaction of 1,4-diazabicyclo[2.2.2]octane with dichloromethane in the presence of R-Br. The co-crystal comprised networks formed by 3:3 or 2:2 halogen bonding between R-Br and Cl−, with the XB lengths varying from 3.0 Å to 3.25 Å. Analysis of the crystallographic database revealed examples of associations with substantially longer and shorter Br…Cl separations. DFT computations of an extended series of R–Br…Cl− complexes confirmed that the judicious choice of brominated electrophile allows varying halogen Br…Cl bond strength and length gradually from the values common for the weak intermolecular complexes to that approaching a fully developed covalent bond. This continuity of halogen bond strength in the experimental (solid-state) and calculated associations indicates a fundamental link between the covalent and supramolecular bonding.

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Anion Recognition by Neutral and Cationic Iodotriazole Halogen Bonding Scaffolds

Molecules ◽

10.3390/molecules25040798 ◽

2020 ◽

Vol 25 (4) ◽

pp. 798

Author(s):

Iñigo Iribarren ◽

Goar Sánchez-Sanz ◽

Cristina Trujillo

Keyword(s):

Density Functional ◽

Computational Study ◽

Halogen Bond ◽

Anion Recognition ◽

Lone Pair ◽

Halogen Bonding ◽

Binding Energies ◽

Bond Critical Point ◽

Density Values ◽

Intramolecular Hydrogen

A computational study of the iodide discrimination by different neutral and cationic iodotriazole halogen bonding hosts was carried out by means of Density Functional Theory. The importance of the size of the scaffold was highlighted and its impact observed in the binding energies and intermolecular X⋯I distances. Larger scaffolds were found to reduce the electronic repulsion and increase the overlap between the halide electron lone pair and the corresponding I-C antibonding orbital, increasing the halogen bonding interactions. Additionally, the planarity plays an important role within the interaction, and can be tuned using hydroxyl to perform intramolecular hydrogen bonds (IMHB) between the scaffold and the halogen atoms. Structures with IMHB exhibit stronger halogen bond interactions, as evidenced by the shorter intramolecular distances, larger electron density values at the bond critical point and more negative binding energies.

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The15N NMR chemical shift in the characterization of weak halogen bonding in solution

Faraday Discussions ◽

10.1039/c7fd00107j ◽

2017 ◽

Vol 203 ◽

pp. 333-346 ◽

Cited By ~ 11

Author(s):

Sebastiaan B. Hakkert ◽

Jürgen Gräfenstein ◽

Mate Erdelyi

Keyword(s):

Hydrogen Bond ◽

Chemical Shift ◽

Halogen Bond ◽

Molar Fraction ◽

Halogen Bonding ◽

Relative Strength ◽

Lewis Base ◽

Halogen Bonds ◽

Bonded Complexes

We have studied the applicability of15N NMR spectroscopy in the characterization of the very weak halogen bonds of nonfluorinated halogen bond donors with a nitrogenous Lewis base in solution. The ability of the technique to detect the relative strength of iodine-, bromine- and chlorine-centered halogen bonds, as well as solvent and substituent effects was evaluated. Whereas computations on the DFT level indicate that15N NMR chemical shifts reflect the diamagnetic deshielding associated with the formation of a weak halogen bond, the experimentally observed chemical shift differences were on the edge of detectability due to the low molar fraction of halogen-bonded complexes in solution. The formation of the analogous yet stronger hydrogen bond of phenols have induced approximately ten times larger chemical shift changes, and could be detected and correlated to the electronic properties of substituents of the hydrogen bond donors. Overall,15N NMR is shown to be a suitable tool for the characterization of comparably strong secondary interactions in solution, but not sufficiently accurate for the detection of the formation of thermodynamically labile, weak halogen bonded complexes.

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Halogen Bonding in N-Alkyl-3-halogenopyridinium Salts

Crystals ◽

10.3390/cryst11101240 ◽

2021 ◽

Vol 11 (10) ◽

pp. 1240

Author(s):

Luka Fotović ◽

Vladimir Stilinović

Keyword(s):

Iodine Atom ◽

Pyridine Ring ◽

Positive Charge ◽

Halogen Bond ◽

Halogen Bonding ◽

Considerable Effect ◽

Halogen Bonds ◽

Bond Lengths ◽

Hirshfeld Surfaces ◽

The One

We performed a structural study of N-alkylated halogenopyridinium cations to examine whether choice of the N-substituent has any considerable effect on the halogen bonding capability of the cations. For that purpose, we prepared a series of N-ethyl-3-halopyridinium iodides and compared them with their N-methyl-3-halopyridinium analogues. Structural analysis revealed that N-ethylated halogenopyridinium cations form slightly shorter C−X⋯I− halogen bonds with iodide anion. We have also attempted synthesis of ditopic symmetric bis-(3-iodopyridinium) dications. Although successful in only one case, the syntheses have afforded two novel ditopic asymmetric monocations with an iodine atom bonded to the pyridine ring and another on the aliphatic N-substituent. Here, the C−I⋯I− halogen bond lengths involving pyridine iodine atom were notably shorter than those involving an aliphatic iodine atom as a halogen bond donor. This trend in halogen bond lengths is in line with the charge distribution on the Hirshfeld surfaces of the cations—the positive charge is predominantly located in the pyridine ring making the pyridine iodine atom σ-hole more positive than the one on the alkyl chan.

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