Dimorphic forms of 3,6-dinitrodurene in a single space group

Area of Science:

• Crystallography
• Solid-state chemistry
• Organic chemistry

Background:

• Polymorphism is a critical phenomenon in solid-state chemistry, influencing material properties.
• 3,6-Dinitrodurene (1,2,4,5-tetramethyl-3,6-dinitrobenzene) is an organic compound known to exist in different crystalline forms.

Purpose of the Study:

• To investigate and characterize the two known polymorphic forms of 3,6-dinitrodurene.
• To elucidate the structural differences responsible for the observed polymorphism and distinct colors.

Main Methods:

• Single-crystal X-ray diffraction was employed to determine the crystal structures of both polymorphs.
• Crystallization experiments were conducted under varying conditions to obtain pure polymorphic forms.

Main Results:

• Two polymorphic forms of 3,6-dinitrodurene were identified, differing in color (colorless vs. purple).
• Both polymorphs crystallize in the space group C2/c, with distinct molecular orientations and conformations of nitro substituents.
• The polymorphism arises from different orientations of the twofold rotation axis within the crystal lattice.

Conclusions:

• The observed color difference in the solid state is directly linked to the distinct crystal structures and molecular arrangements of the two polymorphs.
• Understanding the structural basis of polymorphism in 3,6-dinitrodurene is crucial for controlling its solid-state properties.