Complexes of d- and f-metal ions with pyridine N-oxide and its derivatives: spectroscopic studies

This article reviews results of studies, collected in the literature, related to complexation abilities of pyridine N-oxides, including forms and properties of dand f-metal ion complexes with this group of ligands. In this paper the synthetic pathways of the ligands, based on an oxidation of the corresponding heterocyclic compounds are presented (Scheme 3) [2, 4, 5]. Substituted pyridine N-oxides form an interesting group of compounds, which have found numerous applications [296-299, 314-318]. They have been used in catalysis, crystal engineering, synthesis of coordination polymers, as well as drugs and components in pharmaceutical chemistry [300-309]. Some of them are useful in destroying of microorganisms and the HIV virus [277, 278, 303-307]. Moreover, they are important compounds in the thermal and photochemical oxidation processes [296-299]. The complexes of metal ions with the N-oxide ligands can be formed by binding an oxygen atom of the N›O group, and/or by binding the substituents present in the aromatic ring, e.g. oxygen atoms of carboxylic groups. The complexes can be obtained in monomeric [64, 159], dimeric [58] or polymeric forms [60, 153, 175]. The formation of polymeric forms is more effective when the distance between the positions of COOH and N›O groups in the aromatic ring increases [168]. Complexes of Ln3+ ions and particularly of Eu3+ with pyridine N-oxides are good luminescent materials, better than their heterocyclic counterparts [180, 211]. The emission intensity of europium ions in these systems depends on the efficiency of the LMCT (ligand-metal charge transfer) and LMET (ligand-metal energy transfer) transitions, as well as on electron-donor properties of the substituents present in the pyridine N-oxide ring [37, 132, 155]. A special role in the complexation of Ln3+ ions plays cryptands, which can encapsulate the metal ion. This process protects the metal ion from a penetration of its first coordination sphere by solvent molecules or counterions [245, 246]. The complexes of europium(III) with macromonocyclic, macrobicyclic and acyclic ligands, equipped with photoactive units such as pyridine N-oxide, 2,2'-bipyridine-N,N'-dioxide or 3,3'-biisoquinoline-2,2'-dioxide in solutions, solid states, and incorporated in a silicate matrices by sol-gel method, gained a lot of attention [247-274]

Spectroscopic Characterization of Ethylenediamine-di(o-hydroxyphenyl)acetic Acid and its Complexes with Lanthanide(III) Ions

Binding properties of ethylenediaminedi(o-hydroxyphenyl)acetic acid (EHPG) with lanthanide(III) ions were studied using spectroscopic methods. Luminescence intensity and lifetime of the Tb(III) ion were measured in a wide pH range in order to characterize the Ln-EHPG complexation. The calculated hydration number of the Tb-EHPG system proved the replacement of six water molecules by the EHPG ligand in the inner coordination sphere of Tb(III). Energy transfer from Tb(III) to Eu(III) in the Tb(III)-EHPG-Eu(III) system indicated an existence of only monomeric form of the Tb-EHPG complex. Analysis of the ^1H NMR and FTIR spectra of the EHPG ligand and its complexes with lanthanide(III) ions confirmed the hexadentate manner of EHPG complexation with the lanthanides. The system of Dy(III)-EHPG, showing a linear dependence of luminescence intensity (λ$\text{}_{em}$=578 nm) of Dy(III) on its concentration, in the range of 3.3×10-7 to 1×10-5 mol. l-1, can be applied for spectrofluorimetric determination of Dy(III)

Supramolecular complexes of cobalt(II), manganese(II) and cadmium(II) with bis(terpyridine) ligand as novel luminescent materials

Self-assembly of N6-donor bis(terpyridine) ligand L with transition metal ions: Co(II), Mn(II) and Cd(II) leads to a formation of three kinds of supramolecular complexes. In the electronic absorption and emission spectra of supramolecular complexes additional bands were observed what was ascribed to the coordination of ligand molecules to metal ions. Luminescence properties of these complexes strongly depend on the kind of metal ions and counter ions. The effective blue luminescence was observed in the case of Mn(II) and Cd(II) complexes in which all N-donor atoms of ligand molecules coordinate with the metal center