Metal-ligand interactions in benzodioxotetraaza-macrocyclic metal chelates

Reactions of ethylenediaminetetraacetic (edta) dianhydride with o-phenylene diamine (od) and 9,10-diaminophenanthrene (phn) gave (edtaod)H-2 and (edtap hn)H-2, respectively, in which a chelating edta unit and an aromatic diamin e unit are linked by two amide bonds. The complexation of these new 12-memb ered macrocycles with transition metal ions was studied by X-ray crystallog raphy, potentiometric titrations, UV-Vis absorption spectroscopy and fluore scence spectroscopy. The absorption spectra are sensitively changed by meta l complexation. The spectral changes are the most significant for the Cu2complexes, and are well correlated with the species distribution diagram. T he X-ray study of the Cu2+ complex, [Cu(edtaod)](o), has shown that a squar e plane is formed around the central metal ion by an amide oxygen atom, a c arboxylate oxygen atom and an amino nitrogen atom from a ligand molecule an d a carboxylate oxygen atom from the adjacent chelate molecule. The amide n itrogen atoms in [Cu(edtaod)](o) 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 Cu 2+ ion leads to a strong metal-ligand interaction, which causes an intense charge-transfer band in [Cu(edtaodH(-1))](-), new UV absorption bands in [C u(edtaodH(-2))](2-) and the effective quenching of emission in the Cu2+ com plex of (edtaphn)H-2. (C) 2001 Elsevier Science B.V. All rights reserved.