Interactions of CyMe₄ -BTBP ligand with lanthanides and actinides: Insights from ESI-MS and DFT calculations

Electrospray Ionization Mass Spectrometry (ESI-MS) technique and density functional theory (DFT) calculations were combined to study the formation of the complexes of lanthanides (Ln = La, Ce, Nd, Sm, Eu, Yb) and actinides (UO₂ ²⁺ , Th⁴⁺ ) with CyMe₄ -BTBP (6,6'-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo-[1,2,4-]triazin-3-yl)-[2,2']bipyridine) to understand the mechanisms during the extraction process. Mass spectrometry titrations showed the formation of the complexation in acetonitrile. For lanthanides, only 1:2 complexes ([Ln(L)₂ ]³⁺ , [Ln(L)₂ (CH₃ CN)]³⁺ ), [Ln(L)₂ (NO₃ )]²⁺ ) were found at low [Ln]/[L] concentration ratios, whereas the 1:1 complexes ([Ln(L)(NO₃ )₂ ]⁺ ) were observed when the [Ln]/[L] concentration ratio reached 1.0. For uranyl complexes, 1:1 complex ([UO₂ L(NO₃ )]⁺ ) was the only species within the measuring range. Th⁴⁺ complexes had two compositions: 1:1 and 1:2, in which 1:2 species was the dominant complex. Collision-induced dissociation (CID) was employed to characterize the fragmentation process. The fragmentation process was unfolded sequentially on both sides of CyMe₄ -BTBP ligand with the loss of alkyl groups and cleavage of triazinyl rings. The CID results of CyMe₄ -BTBP complexes revealed a slight difference depending on the metal center. The DFT calculations showed that the stable complexes formed in acetonitrile solution were consistent with the ESI-MS results.