Structure determination from conventional powder diffraction data: application to hydrates, hydrochloride salts, and...

Area of Science:

• Crystallography
• Materials Science
• Computational Chemistry

Background:

• Powder diffraction is increasingly used for crystal structure determination.
• High-intensity synchrotron radiation has improved data quality, but conventional sources also yield reliable data.
• Monte Carlo and simulated annealing methods are powerful computational tools for structure solving.

Purpose of the Study:

• To evaluate Monte Carlo/simulated annealing methods for solving crystal structures using powder diffraction data.
• To demonstrate the applicability of these methods to structures with 9 to 15 degrees of freedom.
• To solve and characterize a metastable polymorphic form of acetohexamide.

Main Methods:

• Structure determination using powder diffraction data.
• Application of Monte Carlo and simulated annealing algorithms.
• Spectroscopic analysis for material characterization.

Main Results:

• Successfully re-determined structures of papaverine hydrochloride and erythromycin A dihydrate using powder diffraction.
• Solved the crystal structure of a metastable polymorphic form (form B) of acetohexamide, which was previously challenging for single-crystal methods due to small crystal size.
• Demonstrated the reliability of powder diffraction with conventional laboratory sources for complex structure determination.

Conclusions:

• Monte Carlo/simulated annealing methods are effective for solving complex crystal structures via powder diffraction.
• Powder diffraction is a viable alternative to single-crystal methods, especially for materials with small or difficult-to-grow crystals.
• This approach expands the scope of crystallographic structure determination for challenging compounds.