Complexation of lanthanides, actinides and transition metal cations with a 6-(1,2,4-triazin-3-yl)-2,2′:6′,2′′-terpyridine ligand: implications for actinide(iii)/lanthanide(iii) partitioning

Abstract

The quadridentate N-heterocyclic ligand 6- (5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2′ : 6′,2′′-terpyridine (CyMe 4 -hemi-BTBP) has been synthesized and its interactions with Am(III), U(VI), Ln(III) and some transition metal cations have been evaluated by X-ray crystallographic analysis, Am(III)/Eu(III) solvent extraction experiments, UV absorption spectrophotometry, NMR studies and ESI-MS. Structures of 1 : 1 complexes with Eu(III), Ce(III) and the linear uranyl (UO 2 2+ ) ion were obtained by X-ray crystallographic analysis, and they showed similar coordination behavior to related BTBP complexes. In methanol, the stability constants of the Ln(III) complexes are slightly lower than those of the analogous quadridentate bis-triazine BTBP ligands, while the stability constant for the Yb(III) complex is higher. 1 H NMR titrations and ESI-MS with lanthanide nitrates showed that the ligand forms only 1 : 1 complexes with Eu(III), Ce(III) and Yb(III), while both 1 : 1 and 1 : 2 complexes were formed with La(III) and Y(III) in acetonitrile. A mixture of isomeric chiral 2 : 2 helical complexes was formed with Cu(I), with a slight preference (1.4 : 1) for a single directional isomer. In contrast, a 1 : 1 complex was observed with the larger Ag(I) ion. The ligand was unable to extract Am(III) or Eu(III) from nitric acid solutions into 1-octanol, except in the presence of a synergist at low acidity. The results show that the presence of two outer 1,2,4-triazine rings is required for the efficient extraction and separation of An(III) from Ln(III) by quadridentate N-donor ligands. † Electronic supplementary information (ESI) available: Procedures and characterization data for known compounds, Mercury plot of ligand 2 and its Eu, Ce and U complexes, NMR stack plots and species distribution curves, enlargements of mass peaks for La(III), Eu(III), Cu(I) and Ag(I) complexes of 2. CCDC 869233-869236. For ESI and crystallographic data in CIF or other electronic format see

Hydrophilic sulfonated bis-1,2,4-triazine ligands are highly effective reagents for separating actinides(iii) from lanthanides(iii) via selective formation of aqueous actinide complexes

“…Moreover, it has been shown that two 1,2,4-triazine moieties are required for efficient and selective extractions by polypyridine N-donor ligands. 18 …”

Crystal structure of 3,3′-di(furan-2-yl)-5,5′-bi-1,2,4-triazine

“…Heterocyclic compounds containing soft donor atoms are capable of separating two groups of elements. For example, it has been reported that ligands containing aromatic N atoms as donor atoms coordinate An(III) more strongly than Ln(III), due to a greater covalent character of the An(III)-N bond [1][2][3]. As a continuation of our structural study on 6,6′-bis(substituted)-5,5′-bi-1,2,4-triazines as potential Nheterocyclic ligands for the extraction of nuclear waste [4], we describe in this paper the crystal structure of 3,3′-di(furan-2-yl)-5,5′-bi-1,2,4-triazine.…”

Exploring the Subtle Effect of Aliphatic Ring Size on Minor Actinide‐Extraction Properties and Metal Ion Speciation in Bis‐1,2,4‐Triazine Ligands

“…To gain furtheri nsighti nto the solution speciation of these ligands with metal ions and to rationalise the extraction results, we carriedo ut some 1 HNMR titrationso ft he ligandsw ith Y III and the diamagnetic lanthanides La III and Lu III .W eh ave previously employed this methodt oi nvestigate the solution speciation of the analogousligands 2 and 3,and relatedtetradentate ligandsw ith trivalentl anthanides. [10a, 19,20] We used deuterated acetonitrile due to the high cost of deuterated 1-octanola nd to compare with previousresults for 2 and 3. [19] For tetradentatel igand 8,b oth 1:1a nd 1:2 M:L species were observed duringt he 1 HNMR titration with Y(NO 3 ) 3 in deuterated acetonitrile.…”