| Abstract
| - The 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridines (DATPs) belong to a new family of extracting agents recentlydeveloped in the framework of nuclear fuel reprocessing. These molecules exhibit exceptional properties to separateactinides(III) from lanthanides(III) in nitric acid solutions. A previous work showed that electrospray ionization massspectrometry (ESI-MS) is a reliable technique to provide solution data such as stoichiometries and conditionalstability constants of various DATP complexes with europium and evidenced the unusual capability of DiPTP [bis(di-iso-propyltriazinyl)pyridine] ligand to form 1:3 complexes in nitric acid solution. This latter result is further investigatedby considering DiPTP complexation features with the complete lanthanide family. As a starting point of the experimentalprocedure used for stability constant evaluation, the intensity distribution of ions detected by ESI-MS is studied forsolutions containing Ln(NO3)3 in water/methanol (1:1 v/v) with the pH value set at 2.8 and 4.6 by HNO3 additions.At pH 2.8, the nitrate anions are found to prevent lanthanides from processes occurring within the ion source: redox phenomena or gas-phase reactions with methanol which give species such as [Ln(MeO)2]+. Thus, the totalintensity of MS signals from [Ln(NO3)2(H2O)p(MeOH)n]+ ions is found proportional to the metal ion concentration. AtpH 4.6, with lower nitrate concentration, the nature of the species identified on mass spectra depends on theelectronic properties of the lanthanide elements. It is shown that Ln(III) complexation with DiPTP leads to theexclusive formation of 1:3 complexes with the whole lanthanide series which may be due not only to the hydrophobicexterior of the ligand but also to the unusual electronic density distribution in DATP ligands as compared with otheraza-aromatic ligands. The conditional stability constants of the 1:3 lanthanide(III) complexes with DiPTP have beendetermined at pH 2.8 and are found to increase almost regularly from La (log β3app = 11.7 ± 0.1) to Lu (log β3app= 16.7 ± 0.8). Moreover, the kinetic stability of the gas-phase 1:3 complexes obtained by electrospray has beeninvestigated by energy-resolved collision-induced dissociation and provides useful information on the bonding andstructure.
- Bis(diisopropyltriazinyl)pyridine belongs to a new family of molecules recently developed in the framework of nuclear fuel reprocessing. This ligand exhibits unusual capabilities to form stable 1:3 complexes with Ln(III) in acidic solutions.
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