Strong Periodic Tendency of Trivalent Lanthanides Coordinated with a Phenanthroline-Based Ligand: Cascade Countercurrent Extraction, Spectroscopy, and Crystallography

Abstract

Phenanthroline-diamide ligands have been reported in the selective separation of actinides over Eu(III); on the contrary, relevant basic coordination chemistry studies are still limited, and extraction under actual application conditions is rarely involved. In this work, N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline [Et-Tol-DAPhen (L)] was applied to explore the coordination performance of lanthanides in simulative high-level liquid waste. For the first time, cascade countercurrent extraction was conducted with Et-Tol-DAPhen as the extractant, which reveals the periodic tendency of the extraction efficiency of lanthanides to decrease gradually as the atomic number increases. Comparison of elements with similar radii verifies the hypothesis that the increase in the atomic number leads to a decrease in the ionic radius, thus reducing the coordination and extraction capacity of ligands. Slope analysis, electrospray ionization mass spectrometry, and ultraviolet−visible titration results show that the ligand forms 1:1 and 1:2 complexes with lanthanides and the coordination ability follows the tendency of extraction efficiency, and the first crystal structures of Lns(III) with a phenanthroline-diamide ligand, i.e., [LaL(NO 3 ) 3 (H 2 O)] and [LaL 2 (NO 3 ) 2 ][(NO 3 )], were obtained, which confirms the conclusions described above. This work promises to enhance our comprehension of the chemical properties of Lns(III) and offer new clues for the design and synthesis of novel separation ligands.

Luminescent Complexes of Europium (III) with 2-(Phenylethynyl)-1,10-phenanthroline: The Role of the Counterions

“…Since the antenna effect is extremely interesting from fundamental point of view, many theoretical and spectroscopic studies discussed the photophysical process of absorption of light, the excited state energy transfer from the ligand to the europium ion and the luminescent properties of these compounds [ 30 , 31 , 32 , 33 , 34 ]. Application-oriented investigations on phenanthroline-based complexes also demonstrated their importance for the advance technologies [ 35 , 36 , 37 , 38 , 39 , 40 ].…”

Atomistic Insights into Structure and Dynamics of Neodymium(III) Complexation with a Bis-lactam Phenanthroline Ligand in the Organic Phase

“…Hard soft acid base theory categorizes the lanthanides as hard electron acceptors, which tend to have a high affinity toward hard O donors. 47 Similar to the Nd(III)–N(BLPhen) distances, Nd(III)–O(BLPhen) distances are also longer in the 2:1 complex than that in the 1:1 complex. Integration of RDFs in Figure 3 b shows that there are two BLPhen oxygen atoms around Nd(III) in the 1:1 complex and four BLPhen oxygen atoms around Nd(III) in the 2:1 complex, as the snapshots in Figure 2 indicate.…”

“…Hard soft acid base theory categorizes the lanthanides as hard electron acceptors, which tend to have a high affinity toward hard O donors. 47 Similar to the Nd(III)− N(BLPhen) distances, Nd(III)−O(BLPhen) distances are also longer in the 2:1 complex than that in the 1:1 complex. Integration of RDFs in Figure 3b shows that there are two 3.3.…”

“… Crystal structures of the complexes from the Cambridge Structural Database (CSD): (a) 1:1 Nd(III)–BLPhen; 17 (b) 2:1 La(III)–DAPhen. 47 Color code: Nd, pink; La, yellow; O, red; N, blue; C, cyan; and H, white. …”

MOFs with 12-Coordinate 5f-Block Metal Centers

“…The large ionic radii of Ln(III, IV) and U(III) are also expected to be able to form such a 12-coordinate PBU in MOFs considering the presence of 12-coordinate homoleptic Ln dicyanonitrosomethanide (Ln = La−Nd, Sm) ionic liquids 33 or heteroleptic lanthanum phenanthroline-diamide complexes. 34 However, it turns out that Ln(III, IV) assemble into an eight-or nine-coordinate Ln-ADC dimer (Figure S12), while U(III) forms a framework (Figure S13a, Figure S16) near identical to U(IV)-ADC, implying that a majority of U(III) is in situ oxidized to U(IV) likely due to the high reactivity of U(III). 35 Further identification of the oxidation kinetics of the U(III) precursor would be needed to pinpoint the synthetic variables that would lead to the formation of 12coordinate trivalent transuranic MOFs.…”