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

Christina D Polyzou; Helen Nikolaou; Catherine P Raptopoulou; Konstantis F Konidaris; Vlasoula Bekiari; Vassilis Psycharis; Spyros P Perlepes

doi:10.3390/molecules26061622

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

Molecules. 2021 Mar 15;26(6):1622. doi: 10.3390/molecules26061622.

Authors

Christina D Polyzou¹, Helen Nikolaou¹, Catherine P Raptopoulou², Konstantis F Konidaris³, Vlasoula Bekiari⁴, Vassilis Psycharis², Spyros P Perlepes^{1

5}

Affiliations

¹ Department of Chemistry, University of Patras, 26504 Patras, Greece.
² Institute of Nanoscience and Nanotechnology, NCSR "Demokritos", 15310 Aghia Paraskevi Attikis, Greece.
³ Department of Pharmacy, University of Patras, 26504 Patras, Greece.
⁴ Department of Crop Science, University of Patras, 30200 Messolonghi, Greece.
⁵ Foundation for Research and Technology-Hellas (FORTH), Institute of Chemical Engineering Sciences (ICE-HT), Platani, B.O. Box 1414, 26504 Patras, Greece.

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 Ln^III-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 Ln^III centers are bridged by two bidentate bridging (η¹:η¹:μ₂) and two chelating-bridging (η¹:η²:μ₂) 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).

Keywords: coordination chemistry; dinuclear lanthanide(III) complexes; magnetic properties of gadolinium(III) complexes; metal complexes of methyl 2-pyridyl ketoxime; photoluminescence studies; single-crystal X-ray structures.

Grants and funding

CA15128/COST ACTION