Dinuclear Lanthanide(III) Complexes from the Use of Methyl 2-Pyridyl Ketoxime: Synthetic, Structural, and Physical Studies

Abstract

The first use of methyl 2-pyridyl ketoxime (mepaoH) in homometallic lanthanide(III) [Ln(III)] chemistry is described. The 1:2 reactions of Ln(NO3)3·nH2O (Ln = Nd, Eu, Gd, Tb, Dy; n = 5, 6) and mepaoH in MeCN have provided access to complexes [Ln2(O2CMe)4(NO3)2(mepaoH)2] (Ln = Nd, 1; Ln = Eu, 2; Ln = Gd, 3; Ln = Tb, 4; Ln = Dy, 5); the acetato ligands derive from the LnIII—mediated hydrolysis of MeCN. The 1:1 and 1:2 reactions between Dy(O2CMe)3·4H2O and mepaoH in MeOH/MeCN led to the all-acetato complex [Dy2(O2CMe)6(mepaoH)2] (6). Treatment of 6 with one equivalent of HNO3 gave 5. The structures of 1, 5, and 6 were solved by single-crystal X-ray crystallography. Elemental analyses and IR spectroscopy provide strong evidence that 2–4 display similar structural characteristics with 1 and 5. The structures of 1–5 consist of dinuclear molecules in which the two LnIII centers are bridged by two bidentate bridging (η1:η1:μ2) and two chelating-bridging (η1:η2:μ2) acetate groups. The LnIII atoms are each chelated by a N,N’-bidentate mepaoH ligand and a near-symmetrical bidentate nitrato group. The molecular structure of 6 is similar to that of 5, the main difference being the presence of two chelating acetato groups in the former instead of the two chelating nitrato groups in the latter. The geometry of the 9-coordinate LnIII centers in 1, 5 and 6 can be best described as a muffin-type (MFF-9). The 3D lattices of the isomorphous 1 and 5 are built through H-bonding, π⋯π stacking and C-H⋯π interactions, while the 3D architecture of 6 is stabilized by H bonds. The IR spectra of the complexes are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The Eu(III) complex 2 displays a red, metal-ion centered emission in the solid state; the TbIII atom in solid 4 emits light in the same region with the ligand. Magnetic susceptibility studies in the 2.0–300 K range reveal weak antiferromagnetic intramolecular GdIII…GdIII exchange interactions in 3; the J value is −0.09(1) cm−1 based on the spin Hamiltonian Ĥ = −J(ŜGd1·ŜGd2).

Confirming the Molecular Basis of the Solvent Extraction of Cadmium(II) Using 2-Pyridyl Oximes through a Synthetic Inorganic Chemistry Approach and a Proposal for More Efficient Extractants

“…The spectra do not exhibit bands that are present in the free ligands 2paoH, 3paoH, 4paoH, dapdoH 2 and LH 4 , suggesting their purity; if such bands were present, the complexes would have been contaminated with the free ligands used as starting materials. The presence of neutral oxime groups in 1 , 2 , 3 and 4 (well-dried unsolvated sample) is manifested by broad bands (with 2–4 submaxima in the spectra of 1 and 4 ) at ~3400 cm −1 assigned to ν (OH) [ 38 , 39 ]. The bands at 3444 and 3292 cm −1 in the IR spectrum of 5 reflect the existence of the imino (=NH) groups in the complex [ 47 ].…”

“…The corresponding bands in the free LH 4 appear at 3484, 3420 and ~3380 cm −1 . The broadness of the ν (OH), ν (NH), ν as (NH 2 ) and ν s (NH 2 ) bands, combined with their relatively low wavenumber, are both indicative of hydrogen bonding [ 38 , 39 ]. As expected, the O-H and N-H stretching vibrations are hardly seen in the Raman spectra of the complexes.…”

“…The spectroscopic studies and the structures of the prepared complexes emphasize the importance of the information emerging from synthetic investigations that otherwise would not have been revealed through exclusively solution studies, while simultaneously shedding light onto the connection of the requisite chemistry with the removal of toxic Cd(II) using pyridyl oxime extractants [ 19 ]. The present work can be considered as a continuation of our intense interest in the coordination chemistry of pyridyl aldo/ketoximes and dioximes, and amidoximes/amidodioximes [ 14 , 27 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 ] and on various aspects of Cd(II) chemistry [ 14 , 40 , 41 , 42 , 43 , 44 , 45 ].…”

Mono- and Mixed Metal Complexes of Eu3+, Gd3+, and Tb3+ with a Diketone, Bearing Pyrazole Moiety and CHF2-Group: Structure, Color Tuning, and Kinetics of Energy Transfer between Lanthanide Ions

“…This phenomenon, called the "antenna effect", underlies the modern approach to creating Ln-based luminescent materials and allows one to avoid the problem of low-efficiency of direct excitation due to low absorption coefficients of rare-earth ions [5,13]. Various conjugated ligands, such as aromatic carboxylic acids [14][15][16], Schiff bases [17] and related compounds [18], as well as various diketones [19][20][21], have been proposed as antennae. Among all possible chelating O,O-bidentate ligands, no doubt, 1,3-diketones are the most important and the most studied up to date.…”

“…Molecules 2021, 26, x FOR PEER REVIEW 2 of 15 acids [14][15][16], Schiff bases [17] and related compounds [18], as well as various diketones [19][20][21], have been proposed as antennae. Among all possible chelating O,O-bidentate ligands, no doubt, 1,3-diketones are the most important and the most studied up to date.…”