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Abstract
Quantum calculations study the potential of an intramolecular H-bond between the halogen atom (X) of a halobenzene and a substituent placed ortho to it, to amplify the ability of X to engage in a halogen bond (XB) with a Lewis base. H-bonding substituents NH2, CH2CH2OH, CH2OH, OH, and COOH were added to halobenzenes (X = Cl, Br, I). The amino group had little effect, but those containing OH increased the CX···N XB energy to a NH3 nucleophile by about 0.5 kcal/mol; the increment associated with COOH is larger, nearly 2 kcal/mol. These energy increments were approximately doubled if two such H-bonding substituents are present. Combining a pair of ortho COOH groups with an electron-withdrawing NO2 group in the para position has a particularly large effect, raising the XB energy by about 4 kcal/mol, which can amount to as much as a 4-fold magnification.
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Affiliation(s)
- Steve Scheiner
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322-0300, United States
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Wacha M, Helm DL, Smart MM, McMillen CD, Casabianca LB, Sachdeva R, Urick CR, Wilson LP, Thrasher JS. A New Motif in Halogen Bonding: Cooperative Intermolecular S-Br⋅⋅⋅O, O⋅⋅⋅F, and F⋅⋅⋅F Associations in the Crystal Packing of α,ω-Di(sulfonyl bromide) Perfluoroalkanes. Chem Asian J 2023; 18:e202300012. [PMID: 36735331 DOI: 10.1002/asia.202300012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2023] [Revised: 02/01/2023] [Accepted: 02/02/2023] [Indexed: 02/04/2023]
Abstract
We recently reported the first examples of S-Cl⋅⋅⋅O halogen bonding complemented by short F⋅⋅⋅F contacts between neighboring chains that resulted in stabilized crystals of ClSO2 (CF2 )4 SO2 Cl and ClSO2 (CF2 )6 SO2 Cl. More recently, other researchers studied our crystallographic data further using an Independent Gradient Model (IGM), and they suggested if one goes beyond IUPAC's proposed 'less than the sum of the van der Waals radii' criterion that even more noncovalent interactions between fluorine atoms on neighboring chains as well as Cl⋅⋅⋅Cl, Cl⋅⋅⋅S, O⋅⋅⋅F, and O⋅⋅⋅S attractive interactions can be found. With that said, we have prepared samples of the related BrSO2 (CF2 )n SO2 Br derivatives (where n=4, 6, 8, and others), which give rise to even stronger S-Br⋅⋅⋅O halogen bonding interactions complemented minimally by O⋅⋅⋅F and F⋅⋅⋅F intermolecular interactions as shown by X-ray crystallography and computational chemistry using IGM isosurface plots. Additional spectroscopic characterization (multinuclear NMR, FT-IR, and MS) of the disulfonyl bromide derivatives BrSO2 (CF2 )4 SO2 Br, BrSO2 (CF2 )6 SO2 Br, and BrSO2 (CF2 )8 SO2 Br has also been obtained as well as some preliminary spectroscopic evidence for BrSO2 (CF2 )2 SO2 Br and BrSO2 CF2 O(CF2 )2 OCF2 SO2 Br. The implication of these results toward the preparation of the corresponding disulfonyl iodides is discussed.
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Affiliation(s)
- Max Wacha
- Institut für Anorganische und Analytische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Str. 7, 60438, Frankfurt am Main, GERMANY.,Department of Chemistry, Clemson University, Advanced Materials Research Laboratory, 91 Technology Drive, Anderson, South Carolina, 29625, USA
| | - David L Helm
- Department of Chemistry, Clemson University, Advanced Materials Research Laboratory, 91 Technology Drive, Anderson, South Carolina, 29625, USA.,Department of Chemistry, Clemson University, Hunter Laboratory, 211 S. Palmetto Blvd., Clemson, South Carolina, 29634, USA
| | - Megan M Smart
- Department of Chemistry, Clemson University, Hunter Laboratory, 211 S. Palmetto Blvd., Clemson, South Carolina, 29634, USA
| | - Colin D McMillen
- Department of Chemistry, Clemson University, Hunter Laboratory, 211 S. Palmetto Blvd., Clemson, South Carolina, 29634, USA
| | - Leah B Casabianca
- Department of Chemistry, Clemson University, Hunter Laboratory, 211 S. Palmetto Blvd., Clemson, South Carolina, 29634, USA
| | - Rakesh Sachdeva
- Department of Chemistry, Clemson University, Hunter Laboratory, 211 S. Palmetto Blvd., Clemson, South Carolina, 29634, USA
| | - Catherine R Urick
- Department of Chemistry, Clemson University, Advanced Materials Research Laboratory, 91 Technology Drive, Anderson, South Carolina, 29625, USA.,Department of Chemistry, Clemson University, Hunter Laboratory, 211 S. Palmetto Blvd., Clemson, South Carolina, 29634, USA
| | - London P Wilson
- Department of Chemistry, Clemson University, Advanced Materials Research Laboratory, 91 Technology Drive, Anderson, South Carolina, 29625, USA.,Department of Chemistry, Clemson University, Hunter Laboratory, 211 S. Palmetto Blvd., Clemson, South Carolina, 29634, USA
| | - Joseph S Thrasher
- Department of Chemistry, Clemson University, Advanced Materials Research Laboratory, 91 Technology Drive, Anderson, South Carolina, 29625, USA.,Department of Chemistry, Clemson University, Hunter Laboratory, 211 S. Palmetto Blvd., Clemson, South Carolina, 29634, USA
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Abstract
Quantum calculations study the manner in which the involvement of a halogen atom as a proton acceptor in one or more H bonds (HBs) affects the strength of the halogen bond (XB) it can form with a nucleophile aligned with the X σ-hole. A variety of Lewis acids wherein X = F, Cl, Br, and I are attached to a tetrel atom C or Ge engaged in a XB with nucleophile NH3. One, two, and three HF molecules were positioned perpendicular to the XB axis so that they could form a HB to the X atom. Each such HB strengthened the XB by an increment of 1 kcal/mol or more that does not attenuate as each new HB is added, potentially increasing the interaction energy manyfold. Additionally, the presence of one or more HBs facilitates the formation of a XB by molecules which are reluctant to engage in such a bond in the absence of these auxiliary interactions. Even the F atom, which avoids such a XB, can be coaxed to participate in a XB of moderate strength by one or more of these external HBs.
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Affiliation(s)
- Steve Scheiner
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322-0300, United States
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Abstract
In addition to the underlying basic concepts and early recognition of halogen bonding, this paper reviews the conflicting views that consistently appear in the area of noncovalent interactions and the ability of covalently bonded halogen atoms in molecules to participate in noncovalent interactions that contribute to packing in the solid-state. It may be relatively straightforward to identify Type-II halogen bonding between atoms using the conceptual framework of σ-hole theory, especially when the interaction is linear and is formed between the axial positive region (σ-hole) on the halogen in one monomer and a negative site on a second interacting monomer. A σ-hole is an electron density deficient region on the halogen atom X opposite to the R–X covalent bond, where R is the remainder part of the molecule. However, it is not trivial to do so when secondary interactions are involved as the directionality of the interaction is significantly affected. We show, by providing some specific examples, that halogen bonds do not always follow the strict Type-II topology, and the occurrence of Type-I and -III halogen-centered contacts in crystals is very difficult to predict. In many instances, Type-I halogen-centered contacts appear simultaneously with Type-II halogen bonds. We employed the Independent Gradient Model, a recently proposed electron density approach for probing strong and weak interactions in molecular domains, to show that this is a very useful tool in unraveling the chemistry of halogen-assisted noncovalent interactions, especially in the weak bonding regime. Wherever possible, we have attempted to connect some of these results with those reported previously. Though useful for studying interactions of reasonable strength, IUPAC’s proposed “less than the sum of the van der Waals radii” criterion should not always be assumed as a necessary and sufficient feature to reveal weakly bound interactions, since in many crystals the attractive interaction happens to occur between the midpoint of a bond, or the junction region, and a positive or negative site.
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