Reaction of Non-Symmetric Schiff Base Metallo-Ligand Complexes Possessing an Oxime Function with Ln Ions

Jean-Pierre Costes,Françoise Dahan,Javier Tojal,Sergiu Shova,Arnaud Dupuis

doi:10.3390/inorganics6010033

Abstract

The preparation of non-symmetric Schiff base ligands possessing one oxime function that is associated to a second function such as pyrrole or phenol function is first described. These ligands, which possess inner N4 or N3O coordination sites, allow formation of cationic or neutral non-symmetric CuII or NiII metallo-ligand complexes under their mono- or di-deprotonated forms. In presence of Lanthanide ions the neutral complexes do not coordinate to the LnIII ions, the oxygen atom of the oxime function being only hydrogen-bonded to a water molecule that is linked to the LnIII ion. This surprising behavior allows for the isolation of LnIII ions by non-interacting metal complexes. Reaction of cationic NiII complexes possessing a protonated oxime function with LnIII ions leads to the formation of original and dianionic (Gd(NO3)5)2− entities that are well separated from each other. This work highlights the preparation of well isolated mononuclear LnIII entities into a matrix of diamagnetic metal complexes. These new complexes complete our previous work dealing with the complexing ability of the oxime function toward Lanthanide ions. It could open the way to the synthesis of new entities with interesting properties, such as single-ion magnets for example.

Highlights

Heterodinuclear complexes associating two different transition metal ions or a transition metal ion with a Lanthanide ion such as Gadolinium are useful in magnetochemistry in order to understand the mechanism of magnetic interactions [1,2]
The complexes possessing the protonated oxime function are obtained by the addition of metal perchlorate to the ligands in a methanol solution without addition of base, while those with deprotonated oxime functions are prepared in acetone with triethylamine as a base
These complexes can be isolated in methanol, but a strong base as NaOH is needed. Reaction of these diverse Ni or Cu complexes with lanthanide salts in acetone yield new entities for which X-ray structural determinations have been of prime interest to obtain their full characterization

Summary

Introduction

Heterodinuclear complexes associating two different transition metal ions or a transition metal ion with a Lanthanide ion such as Gadolinium are useful in magnetochemistry in order to understand the mechanism of magnetic interactions [1,2] Their interest is not limited to this research area and, in view of recent reviews, it is clear that they play a prominent role in catalysis [3,4]. H2 Salen, resulting from condensation of diaminoethane, a diamine synthon, with salicylaldehyde, is a typical Schiff base ligand that is known for long [5] Such a ligand, being able to coordinate a lot of metal ions, was largely used in coordination chemistry. The reactivities of the two amine functions yielding these symmetrical ligands are quite similar, so that the preparation of non-symmetric Schiff

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