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(NO(3))(3)·nH(2)O (Ln = Nd, Eu, Gd, Tb, Dy; n = 5, 6) and mepaoH in MeCN have provided access to complexes [Ln(2)(O(2)CMe)(4)(NO(3))(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(O(2)CMe)(3)·4H(2)O and mepaoH in MeOH/MeCN led to the all-acetato complex [Dy(2)(O(2)CMe)(6)(mepaoH)(2)] (6). Treatment of 6 with one equivalent of HNO(3) 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 (η(1):η(1):μ(2)) and two chelating-bridging (η(1):η(2):μ(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, 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 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 Gd(III…)Gd(III) exchange interactions in 3; the J value is −0.09(1) cm(−1) based on the spin Hamiltonian Ĥ = −J(Ŝ(Gd1)·Ŝ(Gd2)).