Binuclear Copper(II) Chelates of Amide-Based Cyclophanes

Area of Science:

• Coordination Chemistry
• Supramolecular Chemistry
• Spectroscopy

Background:

• Chelating cyclophanes with amino, amide, and carboxymethyl groups were synthesized.
• These ligands feature amide groups directly attached to aromatic systems.
• Previous studies explored related chelating cyclophanes like (bis-edtabpm)H(4) and (bis-edtabpe)H(4).

Purpose of the Study:

• To synthesize novel chelating cyclophanes, specifically (bis-edtapdn)H(4) and (bis-edtanap)H(4).
• To investigate the electronic and EPR spectral properties of their binuclear copper(II) complexes.
• To understand the influence of metal-ligand coordination on spectral and magnetic characteristics.

Main Methods:

• Synthesis of chelating cyclophanes via cyclocondensation reactions.
• Formation of neutral and anionic binuclear copper(II) chelates.
• Characterization using electronic absorption and EPR spectroscopy.

Main Results:

• Water-insoluble neutral binuclear Cu(2+) chelates [Cu(2)L](0) were formed.
• Anionic chelates [Cu(2)(LH(-)(4))](4)(-) exhibited three pi-pi transition bands (240-340 nm), unlike uncoordinated cyclophanes.
• EPR spectrum of [Cu(2)(bis-edtanapH(-)(4))](4)(-) showed hyperfine structure due to spin exchange between Cu(2+) ions.

Conclusions:

• The unusual spectral properties of anionic copper(II) chelates stem from metal-ligand charge transfer and pi-system proximity.
• Coordination with copper significantly influences the absorption and emission spectra of (bis-edtanap)H(4).
• Strong coordination between Cu(2+) ions and deprotonated amide nitrogens bound to pi systems drives the observed spectral and magnetic properties.