A new chromogenic and ratiometric agent for copper(II): Synthesis, structure and spectroscopy

A heterocyclic hydrazone ligand, pyridine-2-carboxaldehyde-2-hydrazino-2-imidazoline hydrobromide, HL (1), was investigated as a new chromogenic and ratiometric agent for selective detection of Cu2+. The ligand 1 gives a characteristic absorption peak in the UV region (λmax = 328 nm). It interacts selectively with Cu2+ and addition of Cu2+ shifted the UV absorption wavelength from 328 to 410 nm due to formation of the complex [CuBr2(HL)] (1a). The red-shift of the absorption spectrum allowed a ratiometric analysis of the signalling behavior. The formation of 1a was accompanied by a color change from light yellow to bright green, which can easily be distinguished from other metal complexes by the naked eye. The association constant (Kass, UV–Vis) of 1a was found to be (5.58 ± 0.006) × 104 at 298 K. The molecular structures of 1 and 1a have been successfully determined by single crystal X-ray diffraction studies.

Graphical abstractA heterocyclic hydrazone ligand, pyridine-2-carboxaldehyde-2-hydrazino-2-imidazoline hydrobromide, was investigated as a new chromogenic and ratiometric agent for selective detection of Cu2+.Figure optionsDownload full-size imageDownload as PowerPoint slide