Extraction and coordination studies of a carbonyl–phosphine oxide scorpionate ligand with uranyl and lanthanide(iii) nitrates: structural, spectroscopic and DFT characterization of the complexes

Abstract

Hybrid scorpionate ligand (OPPh₂)₂CHCH₂C(O)Me (L) was synthesized and characterized by spectroscopic methods and X-ray diffraction. The selected coordination chemistry of L with UO₂(NO₃)₂ and Ln(NO₃)₃ (Ln = La, Nd, Lu) has been evaluated. The isolated mono- and binuclear complexes, namely, [UO₂(NO₃)₂L] (1), [{UO₂(NO₃)L}₂(μ₂-O₂)]·EtOH (2), [La(NO₃)₃L₂]·2.33MeCN (3), [Nd(NO₃)₃L₂]·3MeCN (4), [Nd(NO₃)₂L₂]⁺·(NO₃)⁻·EtOH (5) and [Lu(NO₃)₃L₂] (6) have been characterized by IR spectroscopy and elemental analysis. Single-crystal X-ray structures have been determined for complexes 1–5. Intramolecular intraligand π-stacking interactions between two phenyl fragments of the coordinated ligand(s) were observed in all complexes 1–5. The π-stacking interaction energy was estimated from Bader's AIM theory calculations performed at the DFT level. Solution properties have been examined using IR and multinuclear (¹H, ¹³C, and ³¹P) NMR spectroscopy in CD₃CN and CDCl₃. Coordination modes of L vary with the coordination polyhedron of the metal and solvent nature showing many coordination modes: P(O),P(O), P(O),P(O),C(O), P(O),C(O), and P(O). Preliminary extraction studies of U(VI) and Ln(III) (Ln = La, Nd, Ho, Yb) from 3.75 M HNO₃ into CHCl₃ show that scorpionate L extracts f-block elements (especially uranium) better than its unmodified prototype (OPPh₂)₂CH₂.