Self-assembly as a route to dinuclear lanthanide complexes with rare coordination pattern of salen-type ligand

This contribution is dedicated to Professor Adam Bartecki on the occasion of his 90th birthday.

Abstract

The self-assembled formation of dinuclear lanthanide salicylaldimines is proved by the X-ray diffraction analysis of europium and gadolinium nitrate complexes containing N,N′-bis(salicylidene)-4-methyl-1,3-phenylenediamine (H₂L). The [Eu₂(H₂L)₂(μ-H₂L)₂(NO₃)₆] complex, isostructural with the gadolinium complex, displays nine-coordinate distorted tricapped trigonal prism geometry with a different coordination mode of four undeprotonated salicylaldimines, which act as terminal monodentate and μ-bridging ditopic ligands using exclusively the oxygens as donor atoms with the nitrogen atoms not being involved in the coordination environment. These complexes along with similar lanthanum, erbium, thulium, and lutetium complexes were prepared in situ in a one-step metal promoted condensation reaction between salicylaldehyde and 4-methyl-1,3-phenylenediamine in the presence of lanthanide nitrates. They were isolated and characterized by microanalysis and spectroscopic (IR, ESI–MS, UV–Vis, and ¹H NMR) data with reference to the preformed N,N′-bis(salicylidene)-4-methyl-1,3-phenylenediamine, which was obtained separately and structurally determined by single crystal X-ray analysis.