Lanthanide complexes containing pentadentate s-triazine-based Schiff base ligand: Synthesis, structure and magnetic features

Abstract

Five mononuclear Ln(III) complexes {Ln = Gd (1), Tb (2), Dy (3), Ho (4) and Er (5)} of the general composition [Ln(L)(NO₃)(H₂O)]⋅solv (solv = H₂O and/or DMF) were synthesized and thoroughly characterized. The pentadentate H₂L Schiff base ligand, formed by condensation of 2,4-bishydrazino-6-amino-s-triazine with 3-ethoxysalicylaldehyde, is coordinated to the Ln(III) atoms in the N₃O₂ donor set in an equatorial plane. The coordination geometry of the central metal atoms is then completed by a bidentate-bonded nitrato ligand and one water molecule, thus forming a biaugmented trigonal prism environment, as follows from the X-ray structure of complex 1. A detailed magnetic evaluation (static (dc) and dynamic (ac) data) of complexes 1–5 uncovered that they behave as magnetically diluted paramagnetics with weak antiferromagnetic features originating probably in the presence of non-covalent bonding in the solid samples. Only the complexes of Dy (3) and Er (5) showed signs of slow relaxation of magnetization with the estimated energy barrier values of U_eff = 9.4 (5) K (for 3) and U_eff = 9.9 (6) K (for 5), and relaxation times of τ₀ = 0.25 (8) μs (for 3) and τ₀ = 0.45(9) μs (for 5).