BTBPs versus BTPhens: Some Reasons for Their Differences in Properties Concerning the Partitioning of Minor Actinides and the Advantages of BTPhens

Abstract

Two members of the tetradentate N-donor ligand families 6,6'-bis(1,2,4-triazin-3-yl)-2,2'-bipyridine (BTBP) and 2,9-bis(1,2,4-triazin-3-yl)-1,10-phenanthroline (BTPhen) currently being developed for separating actinides from lanthanides have been studied. It has been confirmed that CyMe4-BTPhen 2 has faster complexation kinetics than CyMe4-BTBP 1. The values for the HOMO-LUMO gap of 2 are comparable with those of CyMe4-BTBP 1 for which the HOMO-LUMO gap was previously calculated to be 2.13 eV. The displacement of BTBP from its bis-lanthanum(III) complex by BTPhen was observed by NMR, and constitutes the only direct evidence for the greater thermodynamic stability of the complexes of BTPhen. NMR competition experiments suggest the following order of bis-complex stability: 1:2 bis-BTPhen complex ≥ heteroleptic BTBP/BTPhen 1:2 bis-complex > 1:2 bis-BTBP complex. Kinetics studies on some bis-triazine N-donor ligands using the stopped-flow technique showed a clear relationship between the rates of metal ion complexation and the degree to which the ligand is preorganized for metal binding. The BTBPs must overcome a significant (ca. 12 kcal mol(-1)) energy barrier to rotation about the central biaryl C-C axis in order to achieve the cis-cis conformation that is required to form a complex, whereas the cis-cis conformation is fixed in the BTPhens. Complexation thermodynamics and kinetics studies in acetonitrile show subtle differences between the thermodynamic stabilities of the complexes formed, with similar stability constants being found for both ligands. The first crystal structure of a 1:1 complex of CyMe4-BTPhen 2 with Y(NO3)3 is also reported. The metal ion is 10-coordinate being bonded to the tetradentate ligand 2 and three bidentate nitrate ions. The tetradentate ligand is nearly planar with angles between consecutive rings of 16.4(2)°, 6.4(2)°, 9.7(2)°, respectively.

Influence of the solvent on the complexation of Cm(iii) and Eu(iii) with nPr–BTP studied by time-resolved laser fluorescence spectroscopy

“…In previous studies numerous different conditions have been applied, most often using a mixture of alcohol (methanol, ethanol or 2-propanol) and water as a solvent. [12][13][14][15][16][17][18][19][20][21][22][23] A comparison of these studies has shown that the water content as well as the alkyl chain of the alcohol have a considerable impact on the stability constants of the formed complexes. 13 Therefore, a detailed knowledge on the influence of the solvent is essential for the comparison of different ligands.…”

The effect of SO3-Ph-BTBP on stainless steel corrosion in nitric acid

“…This may in part be due to the requirement for a conformational change in SO 3 -Ph-BTBP from its preferred trans-conformation to the less favoured cis-conformation prior to metal binding [9,11,12], Fig. 4.…”

“…Such a requirement for a conformational change has been proposed, at least in part, to be responsible for slow kinetics of extraction of both An(III) and Ln(III) species by hydrophobic CyMe 4 based versions of BTBP compared to CyMe 4 based equivalents of BTP and BTPhen [9,11,12]. Thus, we would expect such extraction kinetics to also be slow for Fe 3+ extraction, resulting in the lack of an observed increase in the rate of reductive or transpassive dissolution for both SS304L and SS316L (Figs.…”

“…Furthermore, due to the degradation of BTP ligands under radiolysis [9], radiologically stable sulfonated bistriazinylbipyridine (SO 3 -Ph-BTBP) [10] and 1,10-phenanthroline ligands (SO 3 -Ph--BTPhen) [9,11,12] are currently under investigation as possible replacements for SO 3 -Ph-BTP in the EURO-GANEX process.…”

Selective separation of Am(III) from Eu(III) by 2,9-Bis(dialkyl-1,2,4-triazin-3-yl)-1,10-phenanthrolines: a relativistic quantum chemistry study

“…A striking breakthrough came from the development of another more preorganized tetradentate -heterocyclic ligand, 2,9-bis(1,2,4-triazin-3-yl)-1,10-phenanthroline (BTPhen), by the scientists of Reading University [26][27][28]. BTPhen has been regarded as one of the most promising ligands for the MA(III) separation from highly acidic waste until now.…”