Cadmium(II) and Lead(II) Complexes with Novel Macrocyclic Receptors Derived from 1,10-Diaza-15-crown-5

Abstract

Two novel macrocycles, N,N′-bis(2-aminobenzyl)-1,10-diaza-15-crown-5 (L1) and a non-symmetric cryptand incorporating a pyridinyl Schiff-base spacer (L3), both derived from 1,10-diaza-15-crown-5, have been shown to act as receptors for lead(II) and cadmium(II) guests. The X-ray crystal structures reveal an anti conformation for the free ligand L1, but a syn arrangement in the lead(II) complex, [PbL1](ClO4)2. The corresponding cryptates of L3 can be prepared by simple transmetallation reactions starting from the barium cryptate, showing the preference of L3 for the heavy metal ions. The lead(II) ion, unlike cadmium(II), has been shown to be capable of acting as a template agent in the synthesis of L3. The X-ray crystal structures of the metal cryptates allow an insight into the influence of the nature of the metal ion guest on the conformation of the macrobicyclic receptor L3; the most significant changes are a different folding of the crown and variations in the distance between the two pivotal nitrogen atoms and the imine nitrogen atoms. The cryptand can thus expand or contract its cavity in order to accommodate the different metal ions.