Structural and optical studies of fluoride ion binding using N-heteroaromatic ligands

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Analytical Chemistry

Background:

• N-heteroaromatic systems like 8-hydroxyquinoline and imidazole exhibit strong anion affinity via acidic protons.
• Selective fluoride ion recognition is crucial for various chemical and biological applications.

Purpose of the Study:

• To synthesize and investigate the fluoride ion binding properties of three novel receptor ligands.
• To characterize the fluoride complexes using a combination of spectroscopic, crystallographic, and computational methods.

Main Methods:

• Synthesis of three receptor ligands: 5-(1H-benzo[d]imidazol-2-yl)quinolin-8-ol (1), 5-(benzo[d]thiazol-2-yl)quinolin-8-ol (2), and 4-(1H-benzo[d]imidazol-2-yl)benzene-1,3-diol (3).
• Characterization of fluoride complexes (1-TBAF, 2-TBAF, 3-TBAF) using single crystal X-ray analysis, NMR, UV-vis spectroscopy, Hirshfeld surface analysis, and Density Functional Theory (DFT) studies.

Main Results:

• Ligands 1, 2, and 3 selectively bind fluoride ions through NH, OH, and aryl-CH hydrogen bonding interactions.
• X-ray analysis revealed strong F- binding within the receptor scaffold, with water molecules enhancing binding in complexes 1-TBAF and 3-TBAF.
• NMR studies confirmed NH and OH protons as primary coordination sites for F- ions. UV-vis spectroscopy indicated sensing limits for ligands 1 and 2 at concentrations ≥0.5 μM.
• Hirshfeld surface analysis quantified non-covalent interactions, and DFT studies evaluated electronic properties.

Conclusions:

• The synthesized ligands demonstrate effective and selective fluoride ion binding capabilities.
• The study provides comprehensive structural and electronic insights into fluoride-receptor interactions, paving the way for advanced sensor development.