Pervasive approximate periodic symmetry in organic P1 structures

Area of Science:

• Crystallography
• Materials Science
• Chemical Physics

Background:

• The Cambridge Structural Database (CSD) contains numerous organic crystal structures.
• Understanding symmetry in crystal structures is crucial for predicting material properties and designing new materials.
• P1 space group structures, the least symmetric, offer a unique perspective on deviations from ideal symmetry.

Purpose of the Study:

• To determine the prevalence of approximate symmetry in organic crystal structures within the P1 space group.
• To analyze the types and characteristics of approximate symmetries observed in these structures.
• To investigate the relationship between approximate symmetry and factors like molecular composition and temperature.

Main Methods:

• Analysis of organic crystal structures from the November 2019 CSD release with R-factor ≤ 0.050.
• Systematic identification and classification of structures exhibiting approximate symmetry, including those with Z > 1 and Z = 1.
• Examination of crystal packing and unit cell parameters to identify deviations from ideal symmetry.

Main Results:

• Approximate periodic symmetry was detected in 86% of Z > 1 and 72% of Z = 1 structures.
• Enantiomerically pure structures frequently mimic inversion or rotational symmetry.
• Distorted glide or mirror symmetry is more common in achiral/racemic materials, with 2D periodicity observed more often than 3D.

Conclusions:

• Approximate symmetry is a common feature in organic P1 crystal structures, impacting their packing.
• The type of approximate symmetry observed often correlates with the chirality of the material.
• Further research into approximate symmetry can aid in the rational design of crystalline materials.