Ligand design and metal ion recognition: comparison of the interaction of zinc(II) and cadmium(II) with 17- and 18-membered N 3 O 2 donor macrocycles

Abstract

The interaction of zinc(II) and cadmium(II) with 17- and 18-membered ring macrocycles incorporating nitrogen and oxygen hetero-atoms is reported. These ligands constitute an array of related macrocyclic structures in which the position of the donor atoms, their spacing and the macrocyclic ring size all vary in a systematic manner. Physical measurements confirm the 1:1 metal to ligand stoichiometry of the respective complexes. The complexes, [ML ^1–2H₂O] X₂; [M = Zn(II) or Cd(II); X = Cl or NO₃], have been synthesized via the templated cyclocondensation reactions of salicylaldehyde with 1,2-dibromoethane or 1,3-dibromopropane and diethylenetriamine in 2:1:1 molar ratio. The stoichiometries and coordination modes of the complexes have been deduced from IR, ¹H, and ¹³C NMR, conductivity and microanalytical data. Tetrahedral geometry is suggested for Zn(II) compounds, where three nitrogen atoms are coordinated to the metal and the fourth being occupied by a water molecule, while octahedral geometry is suggested for Cd(II) where three nitrogen and two oxygen atoms are coordinated to the metal, the sixth being occupied by a water molecule.