Structural elucidation of N-amidothiourea derived from nicotinic acid hydrazide: A detailed study of its application as selective anion sensor

Abstract

A novel N-amidothiourea receptor (1), synthesized by the reaction of nicotinic acid hydrazide with phenyl isothiocyanate, was evaluated for the detection of fluoride, acetate, and hydroxide ions selectively over other anions. Receptor 1 was characterized by various spectroscopic methods, and further structural elucidation of it was done by Single Crystal X-ray diffraction analysis. The efficacy of receptor 1 as a colorimetric sensor for fluoride ions was observed by an instant colour change from colourless to light yellow, which can be attributed to the H-bonding complex formation between receptor 1 and anion. The binding characteristics of the thiourea receptor with fluoride ion (F−) showed 1:1 binding stoichiometry at a lower concentration, whereas at a higher concentration, the binding stoichiometry increased to 1:2. The receptor, when treated with acetate and hydroxide ion, showed 1:2 and 1:1 binding stoichiometry, respectively. The binding affinity of receptor 1 was found to be following the Brønsted acidity order, i.e., OH− > AcO− > F−. Detailed quantum chemical calculations also supported the experimental findings.

Keywords

• Thiourea
• Amidothiourea
• Chemosensor
• Brønsted acidity
• Anion binding