Complexation and Extraction of Trivalent Actinides and Lanthanides by Triazinylpyridine N-Donor Ligands

Factors in polypyridyl ligands that control their thermodynamic metal ion selectivity in aqueous solution, and their use in selective fluorescent sensing, are examined. Preorganization of polypyridyl ligands ranging from bidentate to tetradentate by bridging benzo groups, as are present in 1,10-phenanthroline (phen) compared to 2,2′-bipyridyl (bpy), is discussed. The role of solvation is considered in relation to the relative affinity of ligands containing pyridyl groups for divalent and trivalent metal ions in aqueous solution. The effects of steric clashes between H atoms on polypyridyl ligands in decreasing complex stability are evaluated, as well as the effect of chelate ring size on metal ion selectivity. Phen ligands with other donor groups present at the 2 and 9 positions, such as alcohols, amides, carboxylates, and oximes are discussed. The design of pyridyl-based ligands for the separation of Am(III) from lanthanide(III) ions is considered, as well as ligands for the removal of metal ions such as Cu(II) or Zn(II) in neurological diseases such as Alzheimer’s. The design of pyridyl-based fluorescent sensors for selective sensing of metal ions is examined in terms of the role of spin–orbit coupling constants (ζ), paramagnetism, and steric effects in the development of selective fluorescent sensors that operate via chelation enhanced fluorescence (CHEF). It is concluded that for lighter metal ions with smaller ζ values such as Zn(II) and Ca(II), and to a lesser extent Cd(II), that the CHEF effect can be achieved with pyridyl-containing fluorophores that coordinate directly to the metal ion. The way in which steric effects can be used to decrease the CHEF effect in Zn(II) relative to Cd(II) to enable selective sensing of the latter is analyzed. For heavier metal ions such as Hg(II) and Pb(II), because of their large ζ values which quench fluorescence, it is concluded that the fluorophore should be tethered to the metal-binding part of the sensor, and prevented from binding to the metal ion by steric and electronic factors. How Hg(II) can quench the CHEF effect by π-contact with fluorophores such as the anthracenyl group, which at first sight might not seem able to bond with metal ions, is examined.

The pyridyl group in ligand design for selective metal ion complexation and sensing

Abstract Separation of trivalent actinide (An) and lanthanide (Ln) elements is one of the burning topics in the back end of the nuclear fuel cycle due to the similarity in their chemical behaviour. A significant amount of research is being carried out worldwide to develop suitable ligands for the separation of the trivalent actinides and lanthanides. Some of the research groups are engaged in continuous improvement of the di-ethylene-triamine-penta acetic acid (DTPA) based Ln/An separation method, whereas extensive research is going on for the development of the lipophilic and hydrophilic ‘N’ donor heteropolycyclic ligands as the actinide selective ligand. A number of ‘S’ donor ligands are also explored for the Ln/An separation. In the present review, we made an attempt to highlight various separation processes based on soft donor ligands developed for Ln/An separations. Beside the conventional solvent extraction processes, separation possibilities membrane based and solid phase extraction techniques are evaluated for the Ln/An separation and are compiled in the present review.

Separation of trivalent actinides and lanthanides using various ‘N’, ‘S’ and mixed ‘N,O’ donor ligands: a review

Selective separation of radio-cesium from acidic solutions using supported liquid membrane containing chlorinated cobalt dicarbollide (CCD) in phenyltrifluoromethyl sulphone (PTMS)

Liquid-liquid extraction and flat sheet supported liquid membrane studies on Am(III) and Eu(III) separation using 2,6-bis(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine as the extractant.

Ethyl-bis-triazinylpyridine (Et-BTP) for the separation of americium(III) from trivalent lanthanides using solvent extraction and supported liquid membrane methods

A. Roy

Papers

Ethyl-bis-triazinylpyridine (Et-BTP) for the separation of americium(III) from trivalent lanthanides using solvent extraction and supported liquid membrane methods