Structural modification of functionalized carbazoles: from Z' = 1 to Z' = 6

Area of Science:

• Crystallography
• Solid-state chemistry
• Materials science

Background:

• Crystal structures with high numbers of molecules in the asymmetric unit (Z' > 4) are uncommon and offer unique research opportunities.
• Understanding these complex structures aids in advancing crystal structure prediction, crystal engineering, and polymorphism studies.

Purpose of the Study:

• To investigate the crystal structures of three related 2,3,9,9a-tetrahydro-1H-carbazoles.
• To analyze a specific structure exhibiting a high Z' value (Z' = 6) and explore its symmetry and potential phase transitions.
• To correlate variations in Z' values with molecular conformation and intermolecular interactions.

Main Methods:

• Single-crystal X-ray diffraction analysis of three 2,3,9,9a-tetrahydro-1H-carbazole derivatives.
• Symmetry analysis of the crystal structures.
• Comparative structural analysis to identify structure-property relationships.

Main Results:

• One compound displayed an asymmetric unit containing six crystallographically independent molecules (Z' = 6).
• The high-Z' structure showed approximate Fdd2 symmetry, suggesting a link to a low-temperature, symmetry-reducing phase transition.
• Differences in Z' values among the related compounds were attributed to conformational variations and the absence of classical hydrogen bonding.

Conclusions:

• The study successfully characterized complex crystal structures with high Z' values.
• The findings provide evidence for symmetry reduction linked to phase transitions in such systems.
• Conformational flexibility and intermolecular forces significantly influence the molecular packing and Z' values in these tetrahydro-1H-carbazoles.