Competing N vs. P(O),C(O)-coordination in complexes of mono- and bis-1,2,3-triazole ligands modified by carbamoylmethylphosphine oxide fragments with palladium(II), uranyl(II), and lanthanum(III): Solid and solution structures

Six new complexes of three triazole-containing ligands with Pd(II), UO2(II), and La(III) were synthesized and characterized by IR, Raman spectroscopy and X-ray diffraction. Solution structure of complexes was studied by IR and multinuclear NMR spectroscopy. DFT calculations were performed for certain compounds. [Display omitted] Six new complexes [PdCl2(L1)2] (1), [PdCl2(L2)2]·2H2O (2), [PdCl2(L3)] (3), [UO2(L2)(NO3)2]·MeCN, (4), [(UO2)2(L3)(NO3)4] (5), [La(L2)2(NO3)3] (6) (L1 – 1-phenyl-4-propyl-1,2,3-triazole, L2, and L3 – mono- and bis-1,2,3-triazole ligands decorated with carbamoylmethylphosphine oxide (CMPO) fragments, respectively) were synthesized and characterized by elemental analysis and IR and Raman spectroscopy. The structures of complexes 1, 2, 4–6 have been determined by single-crystal X-ray crystallography. The ligands L2 and L3 display P(O),C(O) coordination mode with U(VI), and La(III), but N3 mode with Pd(II) in both solid state and solutions. Various intra- and intermolecular hydrogen bonding interactions involving nitrogen and hydrogen atoms of 1,2,3-triazole fragments were revealed in all studied crystalline complexes irrespective of whether triazole fragment coordinates to metal cation (1, 2) or not 4–6). The complex 1 displayed non-classical triazolyl CH…Cl– hydrogen bonding. These hydrogen bonds were also studied by QTAIM theory. Normal coordinate analysis of the vibrations at the DFT level was performed for the ligand L1 and its complex 1. Solution structure of all complexes has been investigated by IR and multinuclear (1H, 13C, and 31P) NMR spectroscopy. Extraction efficiency of Pd(II), U(VI), and La(III) from 3 M HNO3 into 1,2-dichloroethane using extractants L2 and L3 and the known CMPO extractant – Ph2P(O)CH2C(O)NBu2 is discussed in comparison with structure of the corresponding complexes in solutions.