Eight homodinuclear lanthanide complexes prepared from a quinoline based ligand: structural diversity and single-molecule magnetism behaviour

Abstract

Eight dinuclear lanthanide complexes of compositions [Pr₂L₂(NO₃)₄(H₂O)]·EtOH (1), [Nd₂L₂(NO₃)₄(CH₃CN)]·CH₃CN (2), [Sm₂L₂(NO₃)₄(CH₃CN)]·CH₃CN (3), [Eu₂L₂(NO₃)₄(H₂O)] (4), [Tb₂L₂(NO₃)₄] (5), [Dy₂L₂(NO₃)₄] (6), [Ho₂L₂(NO₃)₄] (7) and [Er₂L₂(NO₃)₄] (8) (HL = 2-{[(2-hydroxy-3-methoxybenzyl)imino]methyl}quinoline-2-formaldehyde) have been synthesized by reactions of Ln(NO₃)₃·6H₂O with a tetradentate quinoline-based Schiff base ligand (HL) in MeCN/EtOH/NEt₃ solution. The structures of 1–8 are characterized by X-ray single crystal diffraction analysis. They exhibit four distinct structures. In complex 1, two Pr^III atoms are triply bridged by three oxygen atoms, including an unusual water bridge. Complexes 2 and 3 are isostructural, in which two metal centres are nine- and ten-coordinated, respectively. There are two characteristic Eu^III ions in 4, which are eight- and ten-coordinated, respectively. In the isomorphous compounds 5–8, the two Ln^III atoms in the centrosymmetric molecules are doubly bridged by phenolate oxygen atoms and both metal ions possess nine-coordinate environments. Dc magnetic susceptibility studies in the 2–300 K range were performed for compounds 6 and 7. Antiferromagnetic interactions were determined for these two complexes. Complex 6 shows slow magnetic relaxation behaviour with an energy barrier (U_eff/K_B) of 14.3 K.