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Halogen Bond Catalysis
Published in Andrew M. Harned, Nonnitrogenous Organocatalysis, 2017
According to the definition proposed by IUPAC, “A halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity.”1 Halogen bond is depicted by “⋯” in the halogen-bonded complex R-X⋯Y; X is a halogen, and Y is an electron donor or Lewis base (Figure 4.1). The basic features of halogen bond are similar to that of hydrogen bond and they are: (a) interatomic distance between X and Y is usually less than the sum of the van der Waals radii, (b) analysis of the electron density topology usually shows a bond path and a (3,−1) bond critical point, (c) nuclear magnetic resonance (NMR) chemical shifts are usually affected by formation of halogen bond, (d) the IR and Raman scattering frequencies of both R-X and Y are affected by halogen bond formation; new vibration modes associated with X⋯Y are also observed, and (e) UV–vis bands of the halogen bond donor usually shift to shorter wavelengths.1
Differential study on the transition from a new polyhalogen-substituted unsymmetric salamo-based ligand to its Cu(II) and Co(II) complexes
Published in Journal of Coordination Chemistry, 2022
Lin Dou, Zhi-Fei Hu, Le-Chuan Feng, Wen-Kui Dong
H2L crystallizes in the triclinic space group P-1 and Z = 2. There is one molecule represented in Figure 4 by its asymmetric unit. The molecular formula is C20H21Br2ClN2O4. As depicted in Figure 4, the molecule is an unsymmetric structure. There are four pairs of important intramolecular hydrogen bonds (C18–H18A···O4, C19–H19C···O4, O1–H1···N1 and O4–H4···N2) in free H2L (figure S4a). Attributed to the introduction of halogen atoms (bromine and chlorine atoms), the presence of one intermolecular halogen bond (Br2…O2 3.049 Å) is of great significance for the structural construction between the two molecules (Figure S4b). Finally, as shown in Figure 5, a three-dimensional supramolecular structure of H2L is generated by different torsion angles and intermolecular hydrogen bonds.
Halogen bond between hypervalent halogens YF3/YF5 (Y=Cl, Br, I) and H2X (X= O, S, Se)
Published in Molecular Physics, 2020
Mingchang Hou, Yanqing Wang, Shubin Yang, Qingzhong Li
Halogen bond is a non-covalent interaction between a halogen atom (Lewis acid) and a neutral or negatively charged Lewis base [1]. In the last ten years, related theoretical and experimental studies have proliferated [2–4]. To better explain the mechanism of halogen bonding, Clark et al. [5], proposed the concept of ‘σ-hole’ in 2007. The σ-hole is an area with positive electrostatic potentials on the halogen atomic surface along the R-Y bond. This σ-hole also confirms the electrostatic feature of halogen bonding and determines its directionality. The better directionality and tuned strength of halogen bonding make it have extensive applications in crystal materials, molecular recognition, chemical reactions and biological systems [6–13]. Of course, there are some exceptions for example in halogen-bonded complexes of CX3I (X = F, Cl, Br, I) with a halide ion or trimethylamine where its strength is opposite to the trend in the σ-hole size [14]. By energy decomposition analysis, it was found that this abnormal trend is a result of charge transfer [15]. The importance of charge transfer was also confirmed in the halogen-bonded complex between ClF and water [16].
2-Chloro-3-fluoropyridine copper(II) complexes and the effect of structural changes on magnetic behavior
Published in Journal of Coordination Chemistry, 2018
Robert J. Dubois, Christopher P. Landee, Melanie Rademeyer, Mark M. Turnbull
As previously observed, the molecular units are linked into chains parallel to the c-axis via a combination of hydrogen (dO1…Cl2A = 3.186(3) Å) and halogen (dCl1…Cl1C = 3.290 Å) bonds (full bonding details are found in Tables 3 and 4, respectively) (Figure 5). Although the hydrogen bond appears to be slightly weaker, based on the D…A distance, the halogen bond is clearly stronger, with a shorter halogen…halide distance and angles closer to 180° and 90°, respectively.