Structural and Spectroscopic Characterization of Two Nitropyridine Amino N-Oxide Derivatives

Area of Science:

• Organic Chemistry
• Materials Science
• Spectroscopy

Background:

• Nitropyridine N-oxide derivatives are of interest for their unique electronic and photophysical properties.
• Understanding structure-property relationships is crucial for designing new functional materials.

Purpose of the Study:

• To synthesize and characterize two new nitropyridine N-oxide derivatives: 3-N-methylamino-4-nitropyridine N-oxide (NOPCH3) and [(4-nitropyridine-3-yl)amino]propanoic acid N-oxide (NOPCOOH).
• To investigate the impact of substituent modification (methyl vs. carboxylic acid) on molecular structure, intermolecular interactions, and spectroscopic properties.

Main Methods:

• Single-crystal X-ray diffraction for molecular and crystal structure determination.
• Hirshfeld surface analysis for intermolecular contact evaluation.
• FT-IR, Raman, UV-Vis, and photoluminescence spectroscopy for vibrational and electronic property analysis.
• Quantum-chemical calculations (DFT) for spectroscopic interpretation.
• Solid-state 13C CP-MAS and 1H WPMLG NMR spectroscopy for chemical constitution confirmation.

Main Results:

• Successful synthesis and structural characterization of NOPCH3 and NOPCOOH.
• Hirshfeld analysis revealed distinct intermolecular contact patterns influenced by the substituents.
• Spectroscopic studies (vibrational and electronic) showed clear differences between NOPCH3 and NOPCOOH, particularly in NO2-related bands and near-UV transitions.
• DFT calculations supported the experimental spectroscopic data.

Conclusions:

• The substitution of a methyl group with a carboxylic acid side chain significantly modifies the hydrogen-bonding network and local electronic environment of the nitropyridine N-oxide core.
• These structural modifications are directly reflected in the observed vibrational and electronic spectroscopic properties.
• The study provides a comprehensive structure-property correlation for these novel compounds, laying the groundwork for future research into their coordination chemistry and photophysical applications.