Exploration of N-oxo pyridine 2-carboxamide ligands towards coordination chemistry, solvent extraction, and DFT investigation for the development of novel solvent for lanthanide and actinide separation. (1st June 2021)

• Record Type: Journal Article
• Authors: Das, Debasish; Joshi, Meenakshi; Kannan, S.; Kumar, Mukesh; Ghanty, Tapan K.; Pente, A.S.; Sengupta, Arijit; Kaushik, C.P.
• Is Part Of: Polyhedron. Volume 201(2021)
• Publication Date: 2021-06-01
• Subjects: Coordination chemistry -- Actinides -- Lanthanides -- Solvent extraction -- Density functional theory; Chemistry, Inorganic -- Periodicals; Chimie inorganique -- Périodiques; Organometaalverbindingen; Anorganische chemie; 546.05
• DOI: 10.1016/j.poly.2021.115166
• Languages: English
• ISSNs: 0277-5387

Abstract

Graphical abstract: The coordination diversity of N -oxo pyridine 2-carboxamide ligands containing N -oxo and amide functional groups towards uranyl nitrate and lanthanide nitrates is reported. Solvent extraction experiments with these ligands show their separation efficacy towards multivalent actinides and lanthanides from aqueous nitric acid medium and discrimination ability for trivalent actinides and lanthanides. Density functional theory calculations corroborate the coordination diversity of these ligands towards uranium and europium and their solvent extraction properties. Abstract: In this study the coordination chemistry of three ligands, C5 H4 NOCONRR′ (where, R, R′ = i C3 H7 (L1); R, R′ = i C4 H9 (L2); and R = H, R′ = t C4 H9 (L3) composed of N -oxide and carboxamide groups have been explored with uranyl nitrate and some selected lanthanide (La, Sm, and Eu) nitrates. All the synthesized ligands as well as their complexes (1 –12 ) of type UO2 (NO3 )2 L (where, L = L1, L2, and L3 for 1, 2, and 3 respectively) and Ln(NO3 )3 (H2 O)L2 (where, Ln = La, L = L1 for 4, L = L2 for 5, and L = L3 for 6 ; Ln = Sm, L = L1 for 7, L = L2 for 8, and L = L3 for 9 ; Ln = Eu, L = L1 for 10, L = L2 for 11, and L = L3 for 12 ) have been characterized by elemental analysis, spectroscopic analyses such as FTIR, 1 H NMR, and electrospray ionization mass spectrometry (ESI-MS). Solid-state structural analysis of L1, 3, and 10 is carried out by X-ray crystallographic technique. The CO and NO groups of L1 are placed almost mutually perpendicular to each other in the crystal structure of L1. The X-ray data show that in [UO2 (NO3 )2 {C5 H4 NOCONH( t C4 H9 )}] (3 ), the ligand acts as a bidentate chelating ligand and is bonded through both the N -oxo and amide oxygen atoms, whereas, in [Eu(NO3 )3 (H2 O){C5 H4 NOCON( i C3 H7 )2 }2 ] (10 ), the ligands show monodentate behavior and are bonded only through N -oxo oxygen atoms. Quantum mechanical calculation at DFT level corroborates the possibility of various bonding modes of these ligands towards uranium and europium nitrate with the preference of bonding as observed in the synthesized complexes. Solvent extraction studies using N, N -dioctyl N -oxo pyridine 2-carboxamide ligand (L4) in n -dodecane with UO2 2+, Pu 4+, Am 3+ and Eu 3+ indicate the trend Pu 4+ ˃ UO2 2+ > Am 3+ > Eu 3+ at acidity range from 0.01 M to 6 M HNO3 . The ligands show good radiation stability at gamma dose up to 500 kGy and chemical stability at 3 M HNO3 for up to 200 h without much affecting the metal ion extraction. Theoretical calculations show the possibility of presence of different metal species in the organic phase, other than the products obtained from dichloromethane during the solvent extraction of UO2 2+ and Eu 3+ in water/dodecane biphasic media. Energy decomposition analysis supports the higher extraction coefficient of UO2 2+ than Eu 3+ with an evidence of higher orbital interaction of the ligands with UO2 2+ .