P1 or P1;? Or something else?

Area of Science:

• Crystallography
• Materials Science
• Chemical Physics

Background:

• The Cambridge Structural Database (CSD) is a key resource for crystal structure data.
• Accurate space group assignment is crucial for correct structural interpretation.
• Previous database releases have contained errors in crystallographic data.

Purpose of the Study:

• To identify and quantify errors in space group assignments within the Cambridge Structural Database.
• To investigate the nature and origin of these space group designation errors.
• To assess the impact of these errors on structural analysis and interpretation.

Main Methods:

• Analysis of unit-cell dimensions and atom coordinates for entries in the CSD (October 1998 release).
• Comparison of reported space group P1 assignments with crystallographic symmetry requirements.
• Evaluation of structural reliability and intermolecular distances based on corrected space group assignments.

Main Results:

• 279 out of nearly 1300 entries assigned to space group P1 were found to have incorrect designations.
• 157 entries with Z > 1 likely resulted from a misprint of the overline in P{\bar 1}.
• 123 entries required revision due to more fundamental errors in space group assignment.
• Chiral molecules in P1 (Z=2) sometimes exhibit pseudocenters of inversion, complicating distinction from P{\bar 1}.

Conclusions:

• A significant number of crystal structures in the CSD were mislabeled, impacting data reliability.
• Distinguishing between P1 and P{\bar 1} can be challenging for structures with deviations from centrosymmetry below ~0.1 Å.
• Revisiting and correcting space group assignments is essential for accurate crystallographic studies.