Metal–ligand interactions in benzodioxotetraaza-macrocyclic metal chelates

• Published in: Inorganica Chimica Acta 2001-11, Vol.324 (1), p.73-80
• Main Authors: Inoue, Michiko B., Machi, Lorena, Muñoz, Iliana C., Rojas-Rivas, Salomon, Inoue, Motomichi, Fernando, Quintus
• Format: Article
• Language: English
• Subjects: Absorption spectra; Luminescence spectra; Macrocyclic metal chelates; Potentiometric titrations; X-ray structures
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/S0020-1693(01)00536-9

Reactions of ethylenediaminetetraacetic (edta) dianhydride with o-phenylenediamine (od) and 9,10-diaminophenanthrene (phn) gave (edtaod)H 2 and (edtaphn)H 2, 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 Cu 2+ complexes, and are well correlated with the species distribution diagram. The X-ray study of the Cu 2+ 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 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 [Cu(edtaodH −2)] 2− and the effective quenching of emission in the Cu 2+ complex of (edtaphn)H 2. The absorption and emission spectra of dioxotetraaza macrocycles that integrate an aromatic group in the ring system are sensitively influenced by complexation with metal ions. These spectral changes are the most significant for the Cu 2+ complexes as a result of a strong metal–ligand interaction operative through the amide nitrogen atoms that link the metal and the aromatic systems.