The many flavours of halogen bonds – message from experimental electron density and Raman spectroscopy

Experimental electron-density studies based on high-resolution diffraction experiments allow halogen bonds between heavy halogens to be classified. The topological properties of the electron density in Cl...Cl contacts vary smoothly as a function of the interaction distance. The situation is less straightforward for halogen bonds between iodine and small electronegative nucleophiles, such as nitrogen or oxygen, where the electron density in the bond critical point does not simply increase for shorter distances. The number of successful charge–density studies involving iodine is small, but at least individual examples for three cases have been observed. (a) Very short halogen bonds between electron-rich nucleophiles and heavy halogen atoms resemble three-centre–four-electron bonds, with a rather symmetric heavy halogen and without an appreciable σ hole. (b) For a narrow intermediate range of halogen bonds, the asymmetric electronic situation for the heavy halogen with a pronounced σ hole leads to rather low electron density in the (3,−1) critical point of the halogen bond; the properties of this bond critical point cannot fully describe the nature of the associated interaction. (c) For longer and presumably weaker contacts, the electron density in the halogen bond critical point is only to a minor extent reduced by the presence of the σ hole and hence may be higher than in the aforementioned case. In addition to the electron density and its derived properties, the halogen–carbon bond distance opposite to the σ hole and the Raman frequency for the associated vibration emerge as alternative criteria to gauge the halogen-bond strength. We find exceptionally long C—I distances for tetrafluorodiiodobenzene molecules in cocrystals with short halogen bonds and a significant red shift for their Raman vibrations.

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Short is strong: experimental electron density in a very short N···I halogen bond

Zeitschrift für Kristallographie - Crystalline Materials ◽

10.1515/zkri-2018-2069 ◽

2018 ◽

Vol 233 (9-10) ◽

pp. 733-744 ◽

Cited By ~ 5

Author(s):

Ruimin Wang ◽

Daniel Hartnick ◽

Ulli Englert

Keyword(s):

Critical Point ◽

Electron Density ◽

Halogen Bond ◽

Bond Critical Point ◽

Total Energy Density ◽

Covalent Bonds ◽

Secondary Interaction ◽

Bona Fide ◽

Atoms In Molecules Theory ◽

Experimental Electron Density

Abstract 2,3,5,6-Tetrafluoro-1,4-diiodobenzene and 4-(dimethylamino)pyridine co-crystallize in 1:2 stoichiometry. A diffraction experiment at standard resolution was already conducted in 2010 and revealed one of the shortest N···I contacts ever reported. We collected X-ray intensities at 100 K up to a very high resolution of 1.23 Å−1. These experimental data allowed to refine a structure model based on atom-centered multipoles according to the Hansen-Coppens approach and provided an experimental electron density. A subsequent analysis with the help of Bader’s atoms in molecules theory showed a strong interaction between the pyridine N atom and the σ hole of its closest iodine neighbor on the halogenated benzene. This contact is characterized by a distance of 2.6622(4) Å and associated with a remarkably large electron density of 0.359(5) e⋅Å−3 in the (3, −1) critical point, unprecedented for a secondary interaction. This bona fide shortest halogen bond ever investigated by an experimental charge density study is associated with a significantly negative total energy density in the bond critical point and thus can reliably be classified as strong. Both the electron density and the position of the bond critical point suggest to compare the short N···I contact to coordinative or covalent bonds rather than to σ hole interactions.

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Can halogen bond energy be reliably estimated from electron density properties at bond critical point? The case of the (A) n Z—Y•••X − (X, Y = F, Cl, Br) interactions

International Journal of Quantum Chemistry ◽

10.1002/qua.25869 ◽

2018 ◽

Vol 119 (8) ◽

pp. e25869 ◽

Cited By ~ 10

Author(s):

Maxim L. Kuznetsov

Keyword(s):

Critical Point ◽

Electron Density ◽

Bond Energy ◽

Halogen Bond ◽

Bond Critical Point

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Comparison of models to correlate electron density at the bond critical point and bond distance

Journal of Molecular Structure THEOCHEM ◽

10.1016/s0166-1280(99)00177-3 ◽

2000 ◽

Vol 496 (1-3) ◽

pp. 131-137 ◽

Cited By ~ 94

Author(s):

I. Alkorta ◽

L. Barrios ◽

I. Rozas ◽

J. Elguero

Keyword(s):

Critical Point ◽

Electron Density ◽

Bond Distance ◽

Bond Critical Point ◽

Correlate Electron

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Strength of the [Z–I···Hal]− and [Z–Hal···I]− Halogen Bonds: Electron Density Properties and Halogen Bond Length as Estimators of Interaction Energy

Molecules ◽

10.3390/molecules26072083 ◽

2021 ◽

Vol 26 (7) ◽

pp. 2083

Author(s):

Maxim L. Kuznetsov

Keyword(s):

Bond Length ◽

Interaction Energy ◽

Electron Density ◽

Halogen Bond ◽

Bond Critical Point ◽

Halogen Bonds ◽

Curvature Potential ◽

Non Covalent Interactions ◽

Covalent Interactions

Bond energy is the main characteristic of chemical bonds in general and of non-covalent interactions in particular. Simple methods of express estimates of the interaction energy, Eint, using relationships between Eint and a property which is easily accessible from experiment is of great importance for the characterization of non-covalent interactions. In this work, practically important relationships between Eint and electron density, its Laplacian, curvature, potential, kinetic, and total energy densities at the bond critical point as well as bond length were derived for the structures of the [Z–I···Hal]– and [Z–Hal···I]– types bearing halogen bonds and involving iodine as interacting atom(s) (totally 412 structures). The mean absolute deviations for the correlations found were 2.06–4.76 kcal/mol.

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"ANTI-HALOGEN" BONDS AS A FACTOR DETERMINING THE TETRAHEDRAL STRUCTURE OF COPPER IN ITS COMPLEXES WITH (5Z, 5'Z)-2,2'- (ETHANE-1,2-DIYLDISULFANYLDIYL)BIS(5-(2-PYRIDYLMETHYLENE)-3-ALLYL-3,5-DIHYDRO- 4H-IMIDAZOLE-4-ONE)

National Association of Scientists ◽

10.31618/nas.2413-5291.2021.2.74.522 ◽

2021 ◽

Vol 2 (74) ◽

pp. 38-41

Author(s):

A. Al-Khazraji ◽

I. Dudkin ◽

E. Ofitserov ◽

A. Finko ◽

E. Beloglazkina

Keyword(s):

Electron Density ◽

Copper Atom ◽

Halogen Bond ◽

Halogen Bonds ◽

Tetrahedral Structure ◽

Angle Of Rotation

Analysis of the valence angles of the Si and carbon atoms of the C-S bond in the obtained complexes of CiVg2 c (5Z, 5'Z)-2,2’-(ethane-1,2-diyldisulfanyldiyl)bis(5-(2-pyridylmethylene)-3-allyl-3,5-dihydro-4Нimidazole-4-one) unambiguously indicates the determinant effect of the non-valent interactions of the electron density centroids of the NEP of bromine atoms and sulfur atoms, leading to a change in the plane structure of Cu(II) towards tetrahedral with a likely change in the magnetochemical properties of the copper atom, and the angle of rotation of the planes is almost 900. This interaction is the opposite of what is commonly called a halogen bond. In this case, it is an "anti-halogen" bond.

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Relationships between Interaction Energy and Electron Density Properties for Homo Halogen Bonds of the [(A)nY–X···X–Z(B)m] Type (X = Cl, Br, I)

Molecules ◽

10.3390/molecules24152733 ◽

2019 ◽

Vol 24 (15) ◽

pp. 2733 ◽

Cited By ~ 6

Author(s):

Maxim L. Kuznetsov

Keyword(s):

Kinetic Energy ◽

Interaction Energy ◽

Electron Density ◽

Bond Critical Point ◽

Kinetic Energy Density ◽

Large Set ◽

Halogen Bonds ◽

Absolute Deviation ◽

The Individual ◽

Best Estimator

Relationships between interaction energy (Eint) and electron density properties at the X···X bond critical point or the d(X···X) distance were established for the large set of structures [(A)nY–X···X–Z(B)m] bearing the halogen bonds Cl···Cl, Br···Br, and I···I (640 structures in total). The best estimator of Eint is the kinetic energy density (Gb), which reasonably approximates the whole set of the structures as −Eint = 0.128Gb2 − 0.82Gb + 1.66 (R2 = 0.91, mean absolute deviation 0.39 kcal/mol) and demonstrates low dispersion. The potential and kinetic energy densities, electron density, and the d(X···X) distance behave similarly as estimators of Eint for the individual series Cl···Cl, Br···Br, and I···I. A number of the Eint(property) correlations are recommended for the practical application in the express estimates of the strength of the homo-halogen bonds.

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Bond length and the electron density at the bond critical point: XX, ZZ, and CZ bonds (X = Li-F, Z = Na-Cl)

Journal of Computational Chemistry ◽

10.1002/jcc.20795 ◽

2007 ◽

Vol 29 (3) ◽

pp. 367-379 ◽

Cited By ~ 15

Author(s):

Norberto Castillo ◽

Katherine N. Robertson ◽

S. C. Choi ◽

Russell J. Boyd ◽

Osvald Knop

Keyword(s):

Bond Length ◽

Critical Point ◽

Electron Density ◽

Bond Critical Point

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Hydrogen vs. Halogen Bonds in 1-Halo-Closo-Carboranes

Materials ◽

10.3390/ma13092163 ◽

2020 ◽

Vol 13 (9) ◽

pp. 2163 ◽

Cited By ~ 3

Author(s):

Ibon Alkorta ◽

Jose Elguero ◽

Josep M. Oliva-Enrich

Keyword(s):

Electron Density ◽

Halogen Bond ◽

Noncovalent Interactions ◽

Decomposition Analysis ◽

Binding Energies ◽

Energy Decomposition Analysis ◽

Bond Critical Point ◽

Total Energy Density ◽

Comparison Of The Results ◽

Intermolecular Distances

A theoretical study of the hydrogen bond (HB) and halogen bond (XB) complexes between 1-halo-closo-carboranes and hydrogen cyanide (NCH) as HB and XB probe has been carried out at the MP2 computational level. The energy results show that the HB complexes are more stable than the XBs for the same system, with the exception of the isoenergetic iodine derivatives. The analysis of the electron density with the quantum theory of atoms in molecules (QTAIM) shows the presence of a unique intermolecular bond critical point with the typical features of weak noncovalent interactions (small values of the electron density and positive Laplacian and total energy density). The natural energy decomposition analysis (NEDA) of the complexes shows that the HB and XB complexes are dominated by the charge-transfer and polarization terms, respectively. The work has been complemented with a search in the CSD database of analogous complexes and the comparison of the results, with those of the 1-halobenzene:NCH complexes showing smaller binding energies and larger intermolecular distances as compared to the 1-halo-closo-carboranes:NCH complexes.

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Experimental observation of charge-shift bond in fluorite CaF2

Acta Crystallographica Section B Structural Science Crystal Engineering and Materials ◽

10.1107/s2052520617008617 ◽

2017 ◽

Vol 73 (4) ◽

pp. 643-653 ◽

Cited By ~ 5

Author(s):

Marcin Stachowicz ◽

Maura Malinska ◽

Jan Parafiniuk ◽

Krzysztof Woźniak

Keyword(s):

Quantum Theory ◽

Density Distribution ◽

Critical Point ◽

Electron Density ◽

Closed Shell ◽

Atoms In Molecules ◽

Bond Critical Point ◽

Ionic Radii ◽

Bond Path ◽

Charge Shift

On the basis of a multipole refinement of single-crystal X-ray diffraction data collected using an Ag source at 90 K to a resolution of 1.63 Å−1, a quantitative experimental charge density distribution has been obtained for fluorite (CaF2). The atoms-in-molecules integrated experimental charges for Ca2+and F−ions are +1.40 e and −0.70 e, respectively. The derived electron-density distribution, maximum electron-density paths, interaction lines and bond critical points along Ca2+...F−and F−...F−contacts revealed the character of these interactions. The Ca2+...F−interaction is clearly a closed shell and ionic in character. However, the F−...F−interaction has properties associated with the recently recognized type of interaction referred to as `charge-shift' bonding. This conclusion is supported by the topology of the electron localization function and analysis of the quantum theory of atoms in molecules and crystals topological parameters. The Ca2+...F−bonded radii – measured as distances from the centre of the ion to the critical point – are 1.21 Å for the Ca2+cation and 1.15 Å for the F−anion. These values are in a good agreement with the corresponding Shannon ionic radii. The F−...F−bond path and bond critical point is also found in the CaF2crystal structure. According to the quantum theory of atoms in molecules and crystals, this interaction is attractive in character. This is additionally supported by the topology of non-covalent interactions based on the reduced density gradient.

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