Competing intermolecular interactions in some 'bridge-flipped' isomeric phenylhydrazones

Area of Science:

• Crystallography
• Organic Chemistry
• Supramolecular Chemistry

Background:

• Phenylhydrazones are versatile organic compounds with potential applications in various fields.
• Understanding their molecular packing is crucial for predicting and controlling their solid-state properties.
• Isomeric variations can lead to significant differences in crystal structures and intermolecular interactions.

Purpose of the Study:

• To investigate how competing intermolecular interactions dictate the distinct molecular packing of isomeric phenylhydrazones.
• To analyze the role of nitrile and nitro groups, along with halogen substituents, in directing crystal assembly.
• To explore the potential for isomorphism in 'bridge-flipped' isomeric pairs.

Main Methods:

• Single-crystal X-ray diffraction was employed to determine the crystal structures of seven substituted phenylhydrazones.
• Comparative analysis of crystal structures was performed to identify similarities and differences in molecular arrangements.
• Hydrogen bonding patterns and other intermolecular interactions were systematically examined.

Main Results:

• Five nitrile-halogen and two nitro-halogen substituted phenylhydrazones were structurally characterized.
• Halogen-exchanged pairs (Ia)/(Ib) and (IIb)/(IIc) were found to be isomorphous.
• No 'bridge-flipped' isomeric pairs, such as (Ib)/(IIb), were isomorphous.
• Nitrile-halogen structures showed N-H---nitrile hydrogen bonds, while nitro-halogen structures exhibited both N-H---nitro and C-H---nitro interactions.
• The C-H---nitro interaction was observed in nitro-halogen structures (III) and (IV).

Conclusions:

• The study highlights the critical role of intermolecular interactions, particularly hydrogen bonding, in differentiating crystal packing of isomeric phenylhydrazones.
• The presence of C-H---nitro interactions in nitro-halogen derivatives opens possibilities for isomorphism in related 'bridge-flipped' isomers.
• These findings contribute to a deeper understanding of structure-property relationships in organic crystalline materials.