Synthesis and characterization of lanthanide complexes prepared with 2-((E)-(1-hydroxy-2-methylpropan-2-ylimino)methyl)-6-methoxyphenol

Abstract

Rare-earth complexes of the general formula [Ln(H₂L₁)₂(NO₃)₃] [Ln = Gd (1), Ho (2) or Nd (3)] were prepared from an o-vanillin derived Schiff base ligand, 2-((E)-(1-hydroxy-2-methylpropan-2-ylimino)methyl)-6-methoxyphenol (H₂L₁). The single-crystal X-ray diffraction studies and SHAPE analyses of the Gd(III) and Ho(III) complexes show that the complexes are ten-coordinate and exhibit distorted tetradecahedron geometries. The phenolate oxygen-bridged dinuclear complex, [Ce₂(H₂L₁)(ovan)₃(NO₃)₃] (4, ovan = monodeprotonated o-vanillin), was obtained from the reaction of Ce(NO₃)₃∙6H₂O with H₂L₁. X-ray analysis revealed that hydrolysis of H₂L₁ occurred to yield o-vanillin, which bridged two cerium atoms with the Ce⋯Ce distance equal to 3.8232(6) Å. The Ce(III) ions are both ten-coordinate, but have different coordination environments, showing tetradecahedron and staggered dodecahedron geometries, respectively. With proton migration occurring from the phenol group to the imine function, complexation of the lanthanides to the ligand gives the Schiff base a zwitterionic phenoxo-iminium form.

Keywords:

• Lanthanide
• bidentate
• crystal structure
• Schiff base
• o-vanillin