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A: New Tools and Methods in Experiment and Theory
Extremely Strong Halogen Bond – the Case of a Double Charge-Assisted Halogen Bridge Malgorzata Domagala, Aneta Lutynska, and Marcin Palusiak J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.8b03735 • Publication Date (Web): 29 May 2018 Downloaded from http://pubs.acs.org on May 29, 2018
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The Journal of Physical Chemistry
Extremely Strong Halogen Bond – the Case of a Double Charge-Assisted Halogen Bridge
Małgorzata Domagała*, Aneta Lutyńska, Marcin Palusiak
Theoretical and Structural Chemistry Group, Faculty of Chemistry, University of Lodz, Pomorska 163/165 90-236 Lodz Poland
[email protected] ACS Paragon Plus Environment
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Abstract The stable model of a double (+/-) charge-assisted halogen bridge has been built on the basis of searches of the Crystal Structure Database. The model, investigated by DFT theory, consists of quinuclidine-like cation derivatives and a set of simple anions. These charged fragments form halogen-bonded complexes of which the energy of complexation in some cases reaches 100 kcal/mol. Even for such strong interactions, the QTAIM characteristics are similar to those of the more classic, relatively weak halogen bonds. An important effect of complexation is the charge transfer measured by means of QTAIM and NBO. It can also be supposed on the basis of detailed structural and QTAIM analysis, that the delocalization of the charge in a quinuclidine moiety occurs through space and not necessarily along formal bonds. The analysis of only partially charged and fully neutral counterparts of a double (+/-) chargeassisted halogen bridge shows significantly weaker bonding, being less than 10 kcal/mol.
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The Journal of Physical Chemistry
Introduction Among different non-covalent interactions, the halogen bond similarly to the hydrogen bond plays an essential role in chemistry and biochemistry.1-14 Extensive analysis of halogen bonds in recent times is a result of the properties of those interaction, which is strong, selective and directional.4-14 Because of these features, halogen bonds have become relevant in crystal engineering.15,16 The A-X…Y halogen bond is the non-covalent interaction where the A-X bond (X usually designates the Cl, Br or I atom, and A is most often the C-atom) acts as a Lewis acid that interacts with the potential electron donor Y (mostly N, O or halogen).17 According to the commonly accepted model of σ-hole,17-23 short halogen bonds in crystalline solids should adopt a linear arrangement. One can see that halogen bonds denote a directional interaction between a potential electron donor Y and a halogen atom X as the electrophile,5 with a lone pair on Y toward the σ-hole of the electrophile of X bonded to the parent C atom. The authors of the concept of the σ-hole, Politzer and co-workers,6-9,13 based on the molecular electrostatic potential, explained that an electron deficiency, the so-called σ-hole, exists at the outer part of the halogen atom, which leads in turn to the electrostatic attraction with Lewis bases. Numerous studies have shown that the strength of halogen bonds correlates with the magnitude of the σ-hole on the halogen atom.16 The electrostatic interaction plays a dominant role in the formation of halogen bonds, but the polarization and dispersion contributions are also noticeable.24-27 The magnitude of the σ-hole is dependent on the nature of halogen atom. The σ-hole potential is more positive, as the halogen atom is more polarizable and has a lower electronegativity. Thus, the strength of the halogen bond increases in the order of F
