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Conventional strategies for materials design have long been used by leveraging primary bonding, such as covalent, ionic, and metallic bonds, between constituent atoms. However, bond energy required to break primary bonds is high. Therefore, high temperatures and enormous energy consumption are often required in processing and manufacturing such materials. On the contrary, intermolecular bonds (hydrogen bonds, van der Waals forces, electrostatic interactions, imine bonds, etc.) formed between different molecules and functional groups are relatively weaker than primary bonds. They, thus, require less energy to break and reform. Moreover, intermolecular bonds can form at considerably longer bond lengths between two groups with no constraint on a specific bond angle between them, a feature that primary bonds lack. These features motivate unconventional strategies for the material design by tuning the intermolecular bonding between constituent atoms or groups to achieve superior physical properties. This paper reviews recent development in such strategies that utilize intermolecular bonding and analyzes how such design strategies lead to enhanced thermal stability and mechanical properties of the resulting materials. The applications of the materials designed and fabricated by tuning the intermolecular bonding are also summarized, along with major challenges that remain and future perspectives that call for further attention to maximize the potential of programming material properties by tuning intermolecular bonding.
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The Balance between Hydrogen Bonds, Halogen Bonds, and Chalcogen Bonds in the Crystal Structures of a Series of 1,3,4-Chalcogenadiazoles
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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- Award ID(s):
- 2018414
- PAR ID:
- 10279671
- Date Published:
- Journal Name:
- Molecules
- Volume:
- 26
- Issue:
- 14
- ISSN:
- 1420-3049
- Page Range / eLocation ID:
- 4125
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The amino group of 2-amino-5-(4-halophenyl)-1,3,4-chalcogenadiazole has been replaced with bromo/iodo substituents to obtain a library of four compositionally related compounds. These are 2-iodo-5-(4-iodophenyl)-1,3,4-thiadiazole, C8H4I2N2S, 2-bromo-5-(4-bromophenyl)-1,3,4-selenadiazole, C8H4Br2N2Se, 2-bromo-5-(4-iodophenyl)-1,3,4-selenadiazole, C8H4BrIN2Se, and 2-bromo-5-(4-iodophenyl)-1,3,4-thiadiazole, C8H4BrIN2S. All were isostructural and contained bifurcated Ch...N (Ch is chalcogen) andX...X(Xis halogen) interactions forming a zigzag packing motif. The noncovalent Ch...N interaction between the chalcogen-bond donor and the best-acceptor N atom appeared preferentially instead of a possible halogen bond to the same N atom. Hirshfeld surface analysis and energy framework calculations showed that, collectively, a bifurcated chalcogen bond was stronger than halogen bonding and this is more structurally influential in this system.more » « less
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Abstract The lone pair of the N atom is a common electron donor in noncovalent bonds. Quantum calculations examine how various aspects of the base on which the N is located affect the strength and other properties of complexes formed with Lewis acids FH, FBr, F2Se, and F3As that respectively encompass hydrogen, halogen, chalcogen, and pnicogen bonds. In most cases the halogen bond is the strongest, followed in order by chalcogen, hydrogen, and pnicogen. The noncovalent bond strength increases in the sp23order of hybridization of N. Replacement of H substituents on the base by a methyl group or substituting N by C atom to which the base N is attached, strengthens the bond. The strongest bonds occur for trimethylamine and the weakest for N2.more » « less
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Type I and II halogen bonds are well-recognized motifs that commonly occur within crystals. Quantum calculations are applied to examine whether such geometries might occur in their closely related chalcogen bond cousins. Homodimers are constructed of the R1R2C=Y and R1R2Y monomers, wherein Y represents a chalcogen atom, S, Se, or Te; R1 and R2 refer to either H or F. A Type II (T2) geometry wherein the lone pair of one Y is closely aligned with a σ-hole of its partner represents a stable arrangement for all except YH2, although not all such structures are true minima. The symmetric T1 geometry in which each Y atom serves as both electron donor and acceptor in the chalcogen bond is slightly higher in energy for R1R2C=Y, but the reverse is true for R1R2Y. Due to their deeper σ-holes, the latter molecules engage in stronger chalcogen bonds than do the former, with the exception of H2Y, whose dimers are barely bound. The interaction energies rise as the Y atom grows larger: S < Se < Te.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/molecules26144125
