A vic-dioxime ligand bearing fluorescent coumarin moieties and its complexes; preparation, spectroscopy, and electrochemistry

Abstract

The synthesis of a new vic-dioxime ligand, N,N′²-dihydroxy-O ¹,O ²-bis(4-methyl-2-oxo-2H-chromen-7-yl)oxalimidamid (LH₂) (1), bearing functional coumarins and its soluble mono- {Ni(II), Cu(II), Co(II)} and dinuclear {UO₂(II)} complexes are presented. The fluorescence properties due to the 7-hydroxy-4-methylcoumarin fluorophore, which is conjugated with vic-dioxime that functions as the MN₄ core of 1 and its complexes, are also reported. The formation of coordination complexes resulted in the blue shift in excitation spectrum and fluorescence quenching of 1. Both mononuclear {(LH)₂M, M=Ni(II), Cu(II), and Co(II)} and homodinuclear {(LH)₂(UO₂)₂(OH)₂)} complexes have been obtained with metal : ligand ratios of 1 : 2 and 2 : 2, respectively. The characterizations of the new compounds were made by elemental analysis, ¹H-NMR, FT-IR, UV-Vis, and LCMS data. Redox behavior of 1, involving oxime and coumarin moieties, and its complexes with Ni(II), Cu(II), Co(II) and UO₂(II) were investigated by cyclic voltammetry. The comparison of the electrochemical behavior of 1 with its complexes enabled us to identify metal-, oxime- and coumarin-based signals.

Keywords:

• Vic-dioxime complexes
• Coumarin
• Fluorescence
• Nickel
• Copper
• Cobalt
• Uranyl
• Cyclic voltammetry

Acknowledgements

We thank the Research Funds of DPT (Project no: 2004; 2003K120970), Marmara University, and the Scientific and Research Council of Turkey [TBAG-AY/397(104T384)] for financial support.