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1. Theoretical, Solid‐State, and Solution Quantification of the Hydrogen Bond‐Enhanced Halogen Bond

   https://doi.org/10.1002/anie.202012262  

   Decato, Daniel A. ; Riel, Asia Marie S. ; May, James H. ; Bryantsev, Vyacheslav S. ; Berryman, Orion B. ( December 2020 , Angewandte Chemie International Edition)

   Proximal noncovalent forces are commonplace in natural systems and understanding the consequences of their juxtaposition is critical. This paper experimentally quantifies for the first time a Hydrogen Bond‐Enhanced Halogen Bond (HBeXB) without the complexities of protein structure or preorganization. An HBeXB is a halogen bond that has been strengthened when the halogen donor simultaneously accepts a hydrogen bond. Our theoretical studies suggest that electron‐rich halogen bond donors are strengthened most by an adjacent hydrogen bond. Furthermore, stronger hydrogen bond donors enhance the halogen bond the most. X‐ray crystal structures of halide complexes (X⁻=Br⁻, I⁻) reveal that HBeXBs produce shorter halogen bonds than non‐hydrogen bond analogues.¹⁹F NMR titrations with chloride highlight that the HBeXB analogue exhibits stronger binding. Together, these results form the foundation for future studies concerning hydrogen bonds and halogen bonds in close proximity.

    

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2. Pushing the limits of the hydrogen bond enhanced halogen bond—the case of the C–H hydrogen bond

   https://doi.org/10.1039/d2sc03792k  

   Decato, Daniel A. ; Sun, Jiyu ; Boller, Madeleine R. ; Berryman, Orion B. ( September 2022 , Chemical Science)

   C–H hydrogen bonds to iodine halogen bond donors are shown to improve halogen bonding and molecular preorganization. 

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3. A Halogen‐Bond‐Induced Triple Helicate Encapsulates Iodide

   https://doi.org/10.1002/ange.201605440  

   Massena, Casey J. ; Wageling, Nicholas B. ; Decato, Daniel A. ; Martin Rodriguez, Enrique ; Rose, Ariana M. ; Berryman, Orion B. ( July 2016 , Angewandte Chemie)

   The self‐assembly of higher‐order anion helicates in solution remains an elusive goal. Herein, we present the first triple helicate to encapsulate iodide in organic and aqueous media as well as the solid state. The triple helicate self‐assembles from three tricationic arylethynyl strands and resembles a tubular anion channel lined with nine halogen bond donors. Eight strong iodine⋅⋅⋅iodide halogen bonds and numerous buried π‐surfaces endow the triplex with remarkable stability, even at elevated temperatures. We suggest that the natural rise of a single‐strand helix renders its linear halogen‐bond donors non‐convergent. Thus, the stringent linearity of halogen bonding is a powerful tool for the synthesis of multi‐strand anion helicates.

    

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4. Intermolecular binding preferences of haloethynyl halogen-bond donors as a function of molecular electrostatic potentials in a family of N -(pyridin-2-yl)amides

   https://doi.org/10.1039/d1ob01133b  

   Abeysekera, Amila M. ; Averkiev, Boris B. ; Le Magueres, Pierre ; Aakeröy, Christer B. ( January 2021 , Organic & Biomolecular Chemistry)

   null (Ed.)

   In order to explore how σ-hole potentials, as evaluated by molecular electrostatic potential (MEP) calculations, affect the ability of halogen atoms to engage in structure-directing intermolecular interactions, we synthesized four series of ethynyl halogen-substituted amide containing pyridines (activated targets); ( N -(pyridin-2-yl)benzamides (Bz-act-X), N -(pyridin-2-yl)picolinamides (2act-X), N -(pyridin-2-yl)nicotinamides (3act-X) and N -(pyridin-2-yl) isonicotinamides (4act-X), where X = Cl/Br/I. The molecules are deliberately equipped with three distinctly different halogen-bond acceptor sites, π, N(pyr), and OC, to determine binding site preferences of different halogen-bond donors. Crystallographic data for ten (out of a possible twelve) new compounds were thus analyzed and compared with data for the corresponding unactivated species. The calculated MEPs of all the halogen atoms were higher in the activated targets in comparison to the unactivated targets and were in the order of iodine ≈ chloroethynyl < bromoethynyl < iodoethynyl. This increased positive σ-hole potential led to a subsequent increase in propensity for halogen-bond formation. Two of the four chloroethynyl structures showed halogen bonding, and all three of the structurally characterized bromoethynyl species engaged in halogen bonding. The analogous unactived species showed no halogen bonds. Each chloroethynyl donor selected a π-cloud as acceptor and the bromoethynyl halogen-bond donors opted for either π or N(pyr) sites, whereas all halogen bonds involving an iodoethynyl halogen-bond donor (including both polymorphs of Bz-act-I ) engaged exclusively with a N(pyr) acceptor site. 

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5. Weak σ‐Hole Triel Bond between C 5 H 5 Tr (Tr=B, Al, Ga) and Haloethyne: Substituent and Cooperativity Effects

   https://doi.org/10.1002/cphc.202000955  

   Yang, Qingqing ; Zhou, Bohua ; Li, Qingzhong ; Scheiner, Steve ( February 2021 , ChemPhysChem)

   The replacement of a CH group of benzene by a triel (Tr) atom places a positive region of electrostatic potential near the Tr atom in the plane of the aromatic ring. This σ‐hole can interact with an X lone pair of XCCH (X=F, Cl, Br, and I) to form a triel bond (TrB). The interaction energy between C₅H₅Tr and FCCH lies in the range between 2.2 and 4.4 kcal/mol, in the order Tr=B+cation above the ring pulls density toward itself and thus magnifies the Tr σ‐hole. The TrB to the XCCH nucleophile is thereby magnified as is the strength of the TrB. This positive cooperativity is particularly large for Tr=B.

    

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