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1. The Balance between Hydrogen Bonds, Halogen Bonds, and Chalcogen Bonds in the Crystal Structures of a Series of 1,3,4-Chalcogenadiazoles

   https://doi.org/10.3390/molecules26144125  

   De Silva, Viraj; Averkiev, Boris B.; Sinha, Abhijeet S.; Aakeröy, Christer B. (July 2021, Molecules)

   null (Ed.)

   In order to explore how specific atom-to-atom replacements change the electrostatic potentials on 1,3,4-chalcogenadiazole derivatives, and to deliberately alter the balance between intermolecular interactions, four target molecules were synthesized and characterized. DFT calculations indicated that the atom-to-atom substitution of Br with I, and S with Se enhanced the σ-hole potentials, thus increasing the structure directing ability of halogen bonds and chalcogen bonds as compared to intermolecular hydrogen bonding. The delicate balance between these intermolecular forces was further underlined by the formation of two polymorphs of 5-(4-iodophenyl)-1,3,4-thiadiazol-2-amine; Form I displayed all three interactions while Form II only showed hydrogen and chalcogen bonding. The results emphasize that the deliberate alterations of the electrostatic potential on polarizable atoms can cause specific and deliberate changes to the main synthons and subsequent assemblies in the structures of this family of compounds. 

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2. Can Twisted Double Bonds Facilitate Stepwise [2 + 2] Cycloadditions?

   https://doi.org/10.1021/acs.orglett.4c00879  

   Viesser, Renan V.; Donald, Clayton P.; May, Jeremy A.; Wu, Judy I. (April 2024, Organic Letters)
3. Structural flexibility of halogen bonds showed in a single-crystal-to-single-crystal [2+2] photodimerization

   https://doi.org/10.1107/S2052252518007583  

   Sinnwell, Michael A.; Blad, Jared N.; Thomas, Logan R.; MacGillivray, Leonard R. (July 2018, IUCrJ)

   Halogen bonds have emerged as noncovalent forces that govern the assembly of molecules in organic solids with a degree of reliability akin to hydrogen bonds. Although the structure-directing roles of halogen bonds are often compared to hydrogen bonds, general knowledge concerning the fundamental structural behavior of halogen bonds has had limited opportunity to develop. Following an investigation of solid-state reactions involving organic syntheses and the development of photoresponsive materials, this work demonstrates the ability of the components of intermolecular N...I halogen bonding – a `workhorse' interaction for the crystal engineer – to support a single-crystal-to-single-crystal [2+2] photodimerization. A comparison is provided of the geometric changes experienced by the halogen-bonded components in the single-crystal reaction to the current crystal landscape of N...I halogen bonds, as derived from the Cambridge Structural Database. Specifically, a linear-to-bent type of deformation of the halogen-bonded components was observed, which is expected to support the development of functional halogen-bonded materials containing molecules that can undergo movements in close-packed crystal environments. 

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4. Cooperativity between H-bonds and tetrel bonds. Transformation of a noncovalent C⋯N tetrel bond to a covalent bond

   https://doi.org/10.1039/D3CP04430K  

   Wang, Xin; Li, Qingzhong; Scheiner, Steve (November 2023, Physical Chemistry Chemical Physics)

   Both a long noncovalent C⋯N tetrel bond and a short covalent C–N bond between imidazole and F₂CO represent minima of comparable energy, when the cooperativity of a H-bond is introduced into the system. 

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5. A diamondoid net sustained by halogen bonds: employing a cyclobutane to generate a tetrahedral architecture

   https://doi.org/10.1039/d0ce00627k  

   Oburn, Shalisa M.; Santana, Carlos L.; Elacqua, Elizabeth; Groeneman, Ryan H. (July 2020, CrystEngComm)

   null (Ed.)

   A halogen-bonded eight-fold interpenetrated diamondoid net was constructed employing a node generated in the solid state. Specifically, co-crystallization of a tetrahedral-like tecton, rctt -tetrakis(4-pyridyl)cyclobutane (4,4′-TPCB), combined with a rigid halogen-bond donor, 1,4-diiodoperchlorobenzene, achieved a diamondoid architecture. In the co-crystal, 4,4′-TPCB is found to form three types of linkages based on one cis - and two trans -orientations enabled by the intrinsic rctt -stereochemisty of the central cyclobutane ring. Thus, 4,4′-TPCB is able to adapt to the constraints of the diamondoid net owing to the flexibility of the pendant 4-pyridyl groups. 

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