Synthesis, characterization, structural analysis of metal(II) complexes of N′-[(E)-3-Bromo-5-Chloro-2-hydroxybenzidene]-4-hydroxybenzohydrazide—Multisubstituted Schiff base as a F− and Cu2+ ions selective chemosensor

• Synthesis of novel multisubstituted hydrazone based Schiff bases.
• Structurally solved Schiff bases for the first time.
• Schiff base is selective sensor for fluoride ion.
• Also acts as chemosensor for cations.

New colorimetric chemosensor, N′-[(E)-3-Bromo-5-Chloro-2-hydroxybenzidene]-4-hydroxybenzohydrazide, containing OH and NH groups as binding sites have been synthesized and characterized by spectral UV, IR, NMR and ESR. The molecular structure of ligand is determined by X-ray crystallography and it has the monoclinic space group P21/c with cell parameters a = 15.1058(6), b = 14.3433(6), c = 17.5800(8) Å and Z = 8. The electronic spectral measurements show that Co2+, Ni2+ and Zn2+ complexes have tetrahedral geometry, while Cu2+ complex has square planar geometry. Magnetic measurements show that Cu2+, Co2+ and Ni2+ complexes have paramagnetic behavior and Zn2+ complex has diamagnetic behavior. Anion binding studies carried out using 1H NMR and UV–visible spectrophotometric titrations revealed that these receptors exhibit selective recognition towards F− over other halide anions. The selectivity for F− among the halides is attributed mainly to the hydrogen-bond interaction of the receptor with F−. Receptor (5 × 10−5 M) shows color change from colorless to yellow in the presence of tetrabutylammonium fluoride (TBAF, 1.5 × 10−3 M). Moreover, F−-induced color changes remain the same even in the presence of large excess of Cl−, Br− and I−. The binding constant is found to be higher towards F− ion and this may be due to presence of OH group, which offers extra binding site. Chromogenic receptor undergoes distinct color changes from colorless to green on gradual addition of Cu2+ can be used as colorimetric probes for spectrophotometric and visual analysis of Cu2+ in the presence of other transition metal ions such as Co2+, Ni2+ and Zn2+.

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