Synthesis and Characterization of Lanthanide(III) Nitrate Complexes of an Hexaaza Macrocyclic Ligand

Abstract

AbstractThe [2+2] barium(II) templated cyclocondensation of 2,6‐diacetylpyridine and ethylendiamine followed by an in situ reduction led to an isomeric mixture of the corresponding saturated macrocycles. The 6S,9S,15R,18R‐meso form of the hexaaza macrocyclic ligand (L) has been obtained by the partial crystallization method. The assignment of the proton and carbon NMR signals was based upon standard COSY, DEPT‐135 and HMQC measurements. The structure of the protonated ligand [H2L](NO3)2·3H2O could be confirmed by X‐ray diffraction. A serie of nitrate lanthanide complexes with L have been prepared. The metal complexes, with general formula [ML](NO3)3·xH2O (M = Nd, Eu, Gd, Tb and Tm), were easily prepared in good yield by direct reaction between the hydrated nitrate metal salt and the macrocyclic ligand. The crystal structure of [NdL(NO3)2](NO3)·H2O has been determined by X‐ray diffraction and shows a mononuclear structure with the neodymium atom in 10‐coordinate with a N6O4 environment. The coordination around the neodymium ion can be described as distorted bicapped cube.