Validation of molecular crystal structures from powder diffraction data with dispersion-corrected density functional...

Area of Science:

• Crystallography
• Materials Science
• Computational Chemistry

Background:

• Single-crystal (SX) structures provide a high-quality benchmark for crystal structure analysis.
• X-ray powder diffraction (XRPD) is a common method for determining organic crystal structures.
• Assessing the accuracy of XRPD structures is crucial for reliable scientific data.

Purpose of the Study:

• To evaluate the quality of 215 organic crystal structures determined by XRPD.
• To compare the accuracy of XRPD structures against a benchmark established using SX structures.
• To identify potential errors and areas for improvement in XRPD-derived crystal structures.

Main Methods:

• Energy minimization of 215 XRPD structures using dispersion-corrected density functional theory (DFT-D).
• Comparison of minimized XRPD structures with 225 pre-existing SX structures.
• Analysis of root mean square Cartesian displacement (RMSCD) values to assess structural accuracy.

Main Results:

• XRPD structures exhibit slightly higher RMSCD values than SX structures after energy minimization.
• Adjusted RMSCD limits (0.35 Å upper, 0.40 Å grey area) are proposed for XRPD structures.
• Energy minimization identified errors in atomic coordinates, hydrogen atom positions, and suggested higher space-group symmetry for some XRPD structures.
• Less than 4% of the analyzed XRPD structures contained errors in non-hydrogen atoms.

Conclusions:

• Molecular crystal structures from XRPD data published in IUCr journals are generally of high quality.
• Energy minimization is a valuable tool for verifying and refining XRPD structures.
• Preferred orientation is a significant factor affecting XRPD data quality.