Powder diffraction study of the hydrogen bonds in nitroxoline and its hydrochloride

Area of Science:

• Crystallography
• Materials Science
• Chemical Physics

Background:

• 8-hydroxy-5-nitroquinoline is a compound with potential applications.
• Understanding crystal structures is crucial for predicting material properties.
• Solubility is a key characteristic influenced by molecular packing.

Purpose of the Study:

• To determine the crystal structures of 8-hydroxy-5-nitroquinoline and 8-hydroxy-5-nitroquinolinium chloride.
• To elucidate the relationship between crystal packing and the physical properties of these compounds.
• To provide insights into the intermolecular interactions governing their solid-state structures.

Main Methods:

• X-ray powder diffraction was employed for crystal structure determination.
• Analysis of hydrogen bonding and molecular packing arrangements.
• Comparison of structural features between the neutral compound and its salt.

Main Results:

• The crystal structure of 8-hydroxy-5-nitroquinoline (I) reveals dimer formation through hydrogen bonds, correlating with low aqueous solubility.
• The crystal structure of 8-hydroxy-5-nitroquinolinium chloride (II) exhibits stacks of cations with anions occupying interstitial spaces.
• Distinct packing motifs were observed for the neutral molecule and its protonated salt.

Conclusions:

• The hydrogen-bonded dimer motif in 8-hydroxy-5-nitroquinoline directly influences its solubility.
• The ionic nature and packing in 8-hydroxy-5-nitroquinolinium chloride lead to a different structural organization.
• Crystal structure analysis provides a fundamental understanding of the properties of nitroquinoline derivatives.