Metal–ligand interactions in benzodioxotetraaza-macrocyclic metal chelates

Reactions of ethylenediaminetetraacetic (edta) dianhydride with o-phenylenediamine (od) and 9,10-diaminophenanthrene (phn) gave (edtaod)H2 and (edtaphn)H2, respectively, in which a chelating edta unit and an aromatic diamine unit are linked by two amide bonds. The complexation of these new 12-membered macrocycles with transition metal ions was studied by X-ray crystallography, potentiometric titrations, UV–Vis absorption spectroscopy and fluorescence spectroscopy. The absorption spectra are sensitively changed by metal complexation. The spectral changes are the most significant for the Cu2+ complexes, and are well correlated with the species distribution diagram. The X-ray study of the Cu2+ complex, [Cu(edtaod)]0, has shown that a square plane is formed around the central metal ion by an amide oxygen atom, a carboxylate oxygen atom and an amino nitrogen atom from a ligand molecule and a carboxylate oxygen atom from the adjacent chelate molecule. The amide nitrogen atoms in [Cu(edtaod)]0 are readily deprotonated and result in the formation of [Cu(edtaodH−1)]− and [Cu(edtaodH−2)]2− in neutral and basic media. The coordination of deprotonated amide nitrogen atoms to a Cu2+ ion leads to a strong metal–ligand interaction, which causes an intense charge-transfer band in [Cu(edtaodH−1)]−, new UV absorption bands in [Cu(edtaodH−2)]2− and the effective quenching of emission in the Cu2+ complex of (edtaphn)H2.