Fluorescent vic-dioxime-type ligand and its mono- and dinuclear complexes: The preparation, spectroscopy, and electrochemistry of its various complexes

A new coumarin functionalized vic-dioxime, S,S-bis-[4-methylcoumarinyl]-dithioglyoxime (LH₂), and its soluble mono- and dinuclear complexes {nickel(II), copper(II), cobalt(II), and uranyl(II)} have been reported. The fluorescent properties of the ligand and its complexes are due to the 7-mercapto-4-methylcoumarin fluorophore, which is conjugated with vic-dioxime that functions as the MN₄ core. Fluorescence spectra of the probe showed a clear shift in excitation wavelength maxima upon metal binding indicating its potential use as ratiometric metal indicator. The fluorescence of complexes was found to be highly sensitive to both polarity and protic character of the solvent used. Both mononuclear (LH)₂M (M = Ni, Cu and Co) and homodinuclear (LH)₂(UO₂)₂(OH)₂) complexes have been obtained with the metal:ligand ratios of 1:2 and 2:2, respectively. The characterizations of all newly synthesized compounds were made by elemental analysis, ¹H NMR, FT-IR, UV-vis, and mass (LSI-MS) data. The electrochemical investigation of the Ni(II), Cu(II), Co(II) and UO₂(II) complexes in comparison with the ligand involving oxime and coumarin moieties enabled us to identify metal-, oxime- and coumarin-based signals.