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Determining the Mechanical Strength of Ultra-Fine-Grained Metals
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Published on: November 22, 2021

Engineering molecular crystals with abnormally weak cohesion.

Kenneth E Maly1, Eric Gagnon, James D Wuest

  • 1Department of Chemistry, Wilfrid Laurier University, Waterloo, Ontario N2L 3C5, Canada. kmaly@wlu.ca

Chemical Communications (Cambridge, England)
|April 1, 2011
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Summary

Methyl groups added to hexaphenylbenzene weaken molecular interactions. This leads to lower sublimation enthalpies, demonstrating how obstructing key interactions creates materials with weak cohesion.

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Area of Science:

  • Materials Science
  • Supramolecular Chemistry
  • Organic Chemistry

Background:

  • Hexaphenylbenzene serves as a foundational structure in materials science.
  • Understanding intermolecular forces, such as C-H···π interactions, is crucial for designing materials with specific properties.
  • Controlling material cohesion impacts applications ranging from crystal engineering to thin-film devices.

Purpose of the Study:

  • To investigate the impact of methyl group substitution on the supramolecular assembly of hexaphenylbenzene derivatives.
  • To determine how targeted modifications affect key intermolecular interactions and bulk material properties.
  • To establish a strategy for designing materials with deliberately weakened cohesive forces.

Main Methods:

  • Synthesis of methylated hexaphenylbenzene derivatives.
  • Crystallographic analysis to identify structural changes and interaction geometries.
  • Differential Scanning Calorimetry (DSC) to measure enthalpies of sublimation.
  • Computational modeling to corroborate experimental findings on C-H···π interactions.

Main Results:

  • Methyl group addition increased molecular weight but reduced the strength of C-H···π interactions.
  • Enthalpies of sublimation were significantly decreased in methylated compounds compared to the parent hexaphenylbenzene.
  • A direct correlation was observed between the weakening of C-H···π interactions and reduced material cohesion.
  • The placement of methyl groups was found to be critical in disrupting the packing and intermolecular forces.

Conclusions:

  • Strategic placement of methyl groups effectively obstructs crucial C-H···π interactions in hexaphenylbenzene.
  • This obstruction leads to materials exhibiting abnormally weak cohesion, evidenced by decreased enthalpies of sublimation.
  • The findings provide a valuable approach for designing novel materials with tailored cohesive properties by identifying and disrupting specific intermolecular interactions.