Cascade detection of fluoride and bisulphate ions by newly developed hydrazine functionalised Schiff bases

Two hydrazine functionalized Schiff bases have been synthesized through the reaction between hydrazine and o-vanillin/salicylaldehyde compounds employing a green-chemical approach and characterized spectroscopically including XRD study. Crystal structure analysis reveals that both the chemosensors, N,N'-bis(o-vanilidine)hydrazine (P17) and N,N'-bis(salicylidene)hydrazine, (HARB) crystallize inmonoclinic systemwith P2(1)/n space group and exist in the locked forms through intramolecular H-bonding (similar to 1.90 angstrom) between phenolic-OH and N atom of hydrazine. The chemosensors display excellent selectivity towards fluoride followed by bisulphate ions, over other potential competitor anions in acetonitrile. Binding stoichiometry of the individual chemosensor with F-is confirmed to be 1:1 and assessed with absorption study and H-1 NMR analysis. Systematic DFT analysis reveals that the contribution of hydroxyl oxygen atoms to the HOMO increases sharply from the chemosensor to chemosensor-F-adduct (17% to 28%) leading to deprotonation of one hydroxyl group and consequently involvement in conjugation impeding the C=Nisomerisation. Thus, the hydroxyl proton captured by F-restricts the C= N isomerisation as well as ICT character of both the chemosensors and confirms the cascade sensing mechanism for fluoride and bisulphate ions. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Two hydrazine functionalized Schiff bases have been synthesized and characterized, displaying excellent selectivity towards fluoride in acetonitrile. Crystal structure analysis reveals they exist in locked forms and contribute to the cascade sensing mechanism for fluoride and bisulphate ions.