Synthesis, crystal structure and sulphide ion sensing study of a Cu(II) complex of aroyl hydrazone

Herein, we report a Cu(II) complex {[CuII(HL)(H2O)2]Cl} of a benzoylhydrazone Schiff base ligand (4-((2-benzoylhydrazineylidene)methyl)-3-hydroxy-5-(hydroxymethyl)-2-methylpyridin-1-ium chloride) (H2L). The molar conductance in solution, magnetic susceptibility, ESI-MS and EPR spectroscopy have been performed to justify the structure of the complex. The solid-state structure of the complex has also been solved by single crystal X-ray diffractometry. Cu(II) centre is penta-coordinated with imine-N, phenoxide-O and deprotonated amide-O donor of the ligand and two H2O molecules occupying the coordination sphere forming a distorted square pyramidal geometry (tau = 0.32). We have studied the anion sensing property of the complex by monitoring the changes in the UV-Vis and fluorescence spectra of the complex in aqueous Tris-HCl buffer medium with incremental addition of various anions as tetrabutylammonium/sodium salts. The complex shows appreciable sensitivity toward sulphide ion, among various other anions, with association constant (Kb) for binding of the complex with S2 and lowest detection limit (L.O.D) value of 6.87 x 104 M 1 and 6.9 x 10 7 M, respectively. Thus, the complex can be used as an efficient S2 probe. The mechanism of sensing is found to be displacement of the fluorescent ligand from the Cu(II) complex by the sulphide ion.