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Powder diffraction and crystal structure prediction identify four new coumarin polymorphs.

Alexander G Shtukenberg1, Qiang Zhu2,3, Damien J Carter4

  • 1Department of Chemistry , Molecular Design Institute , New York University , New York City , NY 10003 , USA .

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Coumarin exhibits rich polymorphism, with four new crystal structures identified from melt-grown forms. Advanced calculations accurately predict polymorph stability, making coumarin a model for crystallization studies.

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Area of Science:

  • Solid-state chemistry
  • Crystallography
  • Computational chemistry

Background:

  • Coumarin, a commodity chemical, has limited known solid-state structures.
  • Polymorphism is crucial for material properties but challenging to predict.

Purpose of the Study:

  • To investigate and report the rich polymorphism of coumarin.
  • To solve crystal structures of new coumarin forms using computational and experimental methods.
  • To establish coumarin as a model system for studying polymorphism and intermolecular interactions.

Main Methods:

  • Melt crystallization
  • Computational crystal structure prediction
  • X-ray powder diffraction
  • Advanced electronic structure calculations (including many-body dispersion)
  • Anharmonic vibrational free energy calculations

Main Results:

  • Four new metastable coumarin polymorphs were identified and their crystal structures solved.
  • Coumarin now exhibits five known crystal structures, demonstrating extensive polymorphism.
  • Advanced computational methods accurately ranked polymorph stability, accounting for dispersion and vibrational effects.

Conclusions:

  • Coumarin is a rare example of a rigid molecule with extensive polymorphism at ambient conditions.
  • Accurate prediction of polymorph stability requires advanced electronic structure and vibrational calculations.
  • Coumarin serves as an excellent model for studying weak interactions, crystallization, and kinetics.