Synthesis and characterization of a crown-ether substituted salicylaldimine Schiff-base ligand and its complexes with cobalt(II), copper(II), nickel(II), and uranyl(VI)

Abstract

15-Formyl-16-hydroxy-2,3,5,6,8,9,11,12-octahydrobenzo[1,4,7,10,13]pentaoxacyclopentadecine (HA) has been synthesised from the corresponding 15-hydroxy substituted crown ether and hexamethylenetetramine in trifluoroacetic acid. Condensation of HA with 1,2-diaminoethane gives the corresponding bis(crown ether) substituted ethylenebis(salicylideneimine) ligand (H₂L). Metal–ligand (1 : 1) complexes of this Schiff base with cobalt(II), copper(II), nickel(II), and uranyl(VI) have been prepared from the corresponding metal acetates. Insertion of sodium ions into the crown ether has been accomplished by refluxing H₂L with sodium nitrate in ethanol. The µ-peroxo compound [{ML(dmso)}₂(µ-O₂)](dmso = dimethyl sulphoxide) was obtained only for M = Co in dmso solution. The order of the formation constants of the complexes determined by the Calvin–Bjerrum pH-titration technique is as follows: [CuL] > [UO₂L] > [NiL] > [CoL].