Concomitant colour polymorphs of (Z)-N-(4-fluorophenyl)-2-oxopropanehydrazonoyl chloride

Area of Science:

• Crystallography
• Solid-state chemistry
• Organic chemistry

Background:

• Polymorphism is a critical phenomenon in solid-state chemistry, influencing material properties.
• Understanding crystal packing and intermolecular forces is key to predicting and controlling polymorphism.

Purpose of the Study:

• To investigate the crystal polymorphism of (Z)-N-(fluorophenyl)-2-oxopropanehydrazonoyl chloride.
• To characterize the structural differences and intermolecular interactions of the observed polymorphs.

Main Methods:

• Recrystallization of the title compound from acetone.
• Single-crystal X-ray diffraction to determine crystal structures and space groups.
• Analysis of intermolecular interactions, specifically hydrogen bonding.

Main Results:

• Two concomitant color polymorphs (form I and form II) were obtained, both belonging to the monoclinic crystal system.
• Form I (pale-orange, block-shaped) and form II (yellow, prism-shaped) exhibit N-H...O hydrogen bonds forming zigzag chains.
• The chains extend via different symmetry operations (2₁ screw in form I, c-glide in form II) and differ in layer corrugation.
• Polymorphs show similar densities, packing indices, and melting points.

Conclusions:

• The study successfully identified and characterized two polymorphs of (Z)-N-(fluorophenyl)-2-oxopropanehydrazonoyl chloride.
• Dominant N-H...O hydrogen bonds dictate the crystal structures, with subtle differences in chain extension and layer arrangement.
• Sublimation behavior differs between polymorphs, with form I transforming to form II, while form II sublimes to itself with altered morphology.