Structural and Thermodynamic Study of the Complexes of Nd(III) with N,N,N′,N′-Tetramethyl-3-oxa-glutaramide and the Acid Analogues

Abstract

The thermodynamics of Nd(III) complexes with N,N,N',N'-tetramethyl-3-oxa-glutaramide (TMOGA, L(I)), N,N-dimethyl-3-oxa-glutaramic acid (DMOGA, HL(II)), and oxydiacetic acid (ODA, H2L(III)) in aqueous solutions was studied. Stability constants, enthalpies, and entropies of complexation were determined by spectrophotometry, potentiometry, and calorimetry. The stability constants of corresponding Nd(III) complexes decrease in the following order: Nd(III)/L(III) > Nd(III)/L(II) > Nd(III)/L(I). For all complexes, the enthalpies of complexation are negative and the entropies of complexation are positive, indicating that the complexation is driven by both enthalpy and entropy. Furthermore, from L(III) to L(II), and to L(I), the enthalpy of complexation becomes more exothermic and the entropy of complexation less positive, suggesting that the substitution of a carboxylate group with an amide group on the ligands enhances the enthalpy-driven force but weakens the entropy-driven force of the complexation with Nd(III). Crystal structures of three 1:3 Nd(III) complexes, Nd(L(I))3(ClO4)3 (I), Nd(L(I))3(NO3)3(H2O)2 (II), and Nd(L(II))3(H2O)7.5 (III), were determined by single-crystal X-ray diffraction and compared with the structure of a 1:3 Nd(III)/L(III) complex in the literature, Na3NdL(III)3(NaClO4)2(H2O)6 (IV). In all four structures, the ligands are tridentate and Nd(III) is nine-coordinated with similar distorted tricapped trigonal prism geometry by three ether oxygen atoms capped on the three faces of the prism, and six oxygen atoms from the ketone group or carboxyl group at the corners. The absorption spectra of Nd(III) in solutions showed very similar patterns as Nd(III) formed successive 1:1, 1:2, and 1:3 complexes with L(I), L(II), and L(III), respectively, implying that the Nd(III) complexes with the three ligands have similar coordination geometries in aqueous solutions, as observed in the solids.

Extraction Behavior of Rare-earth Elements Using a Mono-alkylated Diglycolamic Acid Extractant

“…Recently, a similar geometry of the RE-DGAA complex was reported by Tian et al in their studies on the Nd-DGAA complex prepared by N,N-dimethyldiglycolamic acid with a tertiary amide group [26].…”

Highly Efficient Extraction of Trivalent f‐Cations Using Several N‐Pivot Tripodal Diglycolamide Ligands in an Ionic Liquid: The Role of Ligand Structure on Metal Ion Complexation

“…3–4 mmol/L to which a calculated aliquot of the titrant (ligand solution in C 8 mim · Tf 2 N) was added. Similar titrations at macroconcentration of Nd 3+ with water soluble DGA ligands have been performed earlier with large stability constant values . The stability constant data were further verified by the potentiometric titration suggesting that the absorption spectroscopy technique can be used for obtaining complex formation data having large stability constant values.…”

Coordination of 2,2′-(Trifluoroazanediyl)bis(N,N′-dimethylacetamide) with U(VI), Nd(III), and Np(V): A Thermodynamic and Structural Study

“…To help understand the thermodynamic and structural properties of the actinide complexes with DGA ligands, a number of studies have been conducted in recent years by using small alkyl groups (e.g., methyl) to render the DGA ligands watersoluble so that a variety of techniques, such as potentiometry, spectrophotometry, and calorimetry, are applicable to the studies. [12,13,14,15] The alkyl-substituted DGA ligands are usually tridentate to the metal ions, using the two amide oxygen atoms and the center ether oxygen. 4 [12,13,14,15] Considering that no substitutional groups can be attached to the ether oxygen of DGA to vary the basicity and binding strength of the ligands, we have previously synthesized and conducted the studies of a series of structurally related amine-bridged diacetamide ligands, including…”

“…It has been demonstrated that these ligands form stronger complexes with Nd 3+ , [16] UO 2 2+ , [17] or NpO 2 + , [18] than TMDGA. [12,13,15] In a tridentate mode similar to the DGA ligands, the amine-bridged diacetamides coordinate to the metal ions via the two amide oxygen atoms and the central nitrogen.…”