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

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)center dot nH(2)O (Ln = Nd, Eu, Gd, Tb, Dy; n = 5, 6) and mepaoH in MeCN have provided access to complexes [Ln(2)(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 Ln(III)-mediated hydrolysis of MeCN. The 1:1 and 1:2 reactions between Dy(O2CMe)(3)center dot 4H(2)O and mepaoH in MeOH/MeCN led to the all-acetato complex [Dy-2(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 Ln(III) centers are bridged by two bidentate bridging (eta(1):eta(1):mu(2)) and two chelating-bridging (eta(1):eta(2):mu(2)) acetate groups. The Ln(III) 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 Ln(III) 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, pi MIDLINE HORIZONTAL ELLIPSIS pi stacking and C-HMIDLINE HORIZONTAL ELLIPSIS pi 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 Tb-III 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 (GdGdIII)-Gd-III horizontal ellipsis exchange interactions in 3; the J value is -0.09(1) cm(-1) based on the spin Hamiltonian = -J((Gd1)center dot(Gd2)).

Automated summary

This study introduces the first use of methyl 2-pyridyl ketoxime (mepaoH) in homometallic lanthanide(III) [Ln(III)] chemistry, detailing the synthesis and structural characteristics of complexes formed with various metal ions. Structural analysis through single-crystal X-ray crystallography, elemental analyses, and IR spectroscopy reveal the similarities among the synthesized complexes. Additionally, the complexes exhibit different luminescent properties and magnetic behaviors in the solid state, as observed through magnetic susceptibility studies.