Polymorphism of maleic hydrazide. I

Area of Science:

• Crystallography
• Solid-state chemistry
• Materials science

Background:

• Maleic hydrazide (MH) exists in multiple crystalline forms (polymorphs).
• Understanding polymorphism is crucial for controlling material properties.
• Previous studies identified MH1 (triclinic) and MH2 (monoclinic) polymorphs.

Purpose of the Study:

• To characterize the crystal structure of the third polymorph of maleic hydrazide (MH3).
• To compare the structural features and supramolecular arrangements of MH3 with known polymorphs MH1 and MH2.
• To analyze the relationship between crystal symmetry, supramolecular conformation, and crystal packing.

Main Methods:

• X-ray diffraction analysis was used to determine the crystal structure of MH3.
• Single crystal X-ray diffraction was employed for the redetermination of MH1 structure.
• Comparative analysis of crystal structures and hydrogen bonding patterns.

Main Results:

• The third polymorph, MH3, was identified as monoclinic with space group P2(1)/n.
• MH3 was found coexisting with the rare triclinic MH1 (space group P1).
• MH3 exhibits hydrogen-bonded ribbons similar to MH1 and MH2, but with distinct aggregate arrangements and supramolecular conformations.

Conclusions:

• The crystal structure of maleic hydrazide polymorph MH3 has been elucidated.
• Differences in supramolecular conformation and aggregate arrangement distinguish MH3 from MH1 and MH2.
• The study provides insights into how supramolecular conformations adapt to crystal packing requirements and influence polymorph symmetry.