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π covalency in the halogen bond.

ABSTRACT: Halogen bonds are a highly directional class of intermolecular interactions widely employed in chemistry and chemical biology. This linear interaction is commonly viewed to be analogous to the hydrogen bond because hydrogen bonding models also intuitively describe the σ-symmetric component of halogen bonding. The possibility of π-covalency in a halogen bond is not contemplated in any known models. Here we present evidence of π-covalency being operative in halogen bonds formed between chloride and halogenated triphenylamine-based radical cations. We reach this conclusion through computational analysis of chlorine K-edge X-ray absorption spectra recorded on these halogen bonded pairs. In light of this result, we contend that halogen bonding is better described by analogy to metal coordination bonds rather than hydrogen bonds. Our revised description of the halogen bond suggests that these interactions could be employed to influence the electronic properties of conjugated molecules in unique ways.

SUBMITTER: Kellett CW

PROVIDER: S-EPMC7335087 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature

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π covalency in the halogen bond.

Kellett Cameron W CW Kennepohl Pierre P Berlinguette Curtis P CP

Nature communications 20200703 1

Halogen bonds are a highly directional class of intermolecular interactions widely employed in chemistry and chemical biology. This linear interaction is commonly viewed to be analogous to the hydrogen bond because hydrogen bonding models also intuitively describe the σ-symmetric component of halogen bonding. The possibility of π-covalency in a halogen bond is not contemplated in any known models. Here we present evidence of π-covalency being operative in halogen bonds formed between chloride an ...[more]

PMID: 32620765

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Project description:Recently, noncovalent interactions in complexes and crystals have attracted considerable interest. The current study was thus designed to gain a better understanding of three seminal types of noncovalent interactions, namely: hydrogen, halogen and tetrel interactions with π-systems. This study was performed on three models of Lewis acids: X3-C-H, F3-C-X and F-T-F3 (where X = F, Cl, Br and I; and T = C, Si, Ge and Sn) and three π-systems as Lewis bases: benzene (BZN), 1,3,5-trifluorobenzene (TFB) and hexafluorobenzene (HFB). Quantum mechanical calculations, including geometrical optimization, molecular electrostatic potential (MEP), maximum positive electrostatic potential (V s,max), Point-of-Charge (PoC), potential energy surface (PES), quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) calculations, were carried out at the MP2/aug cc-pVDZ level of theory. The binding energies were additionally benchmarked at the CCSD(T)/CBS level. The results showed that: (i) the binding energies of the X3-C-H⋯π-system complexes were unexpectedly inversely correlated with the V s,max values on the hydrogen atom but directly correlated with the X atomic sizes; (ii) the binding energies for the F3-C-X⋯π-system and F-T-F3⋯π-system complexes were correlated with the σ-hole magnitudes of the X and T atoms, respectively; and (iii) for the F3-C-F⋯π-system complexes, the binding energy was as strong as the π-system was electron-deficient, indicating the dominating nucleophilic character of the fluorine atom. NCI analysis showed that the unexpected trend of X3-C-H⋯π-system binding energies could be attributed to additional attractive interactions between the X atoms in the X3-C-H molecule and the carbon atoms of the π-system. Furthermore, the I3-Sn-H molecule was employed as a case study of hydrogen, halogen and tetrel interactions with π-systems. It was found that hydrogen and halogen interactions of the I3-Sn-H molecule correlated with the electron-richness of the π-system. In contrast, tetrel interactions correlated with the electron deficiency of the π-system.

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π covalency in the halogen bond.

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π covalency in the halogen bond.

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