SYNTHESIS, MOLECULAR STRUCTURE AND MAGNETIC PROPERTIES OF TETRANUCLEAR COPPER(II) COMPLEXES WITH PENDANT-ARM MACROCYCLIC LIGANDS

Abstract

The study of multidentate chelating agents has been stimulated by a phenomenon in living organisms and their numerous practical applications. This interest has led to the creation and investigation of a wide range of multidentate ligands, specifically derived from compounds based on pyridine. Pyridine-based multidentate compounds are versatile chelating agents for several reasons, including their ability to function as bi-, tri-, or tetra-dentate ligands and their potential to bridge to metal atoms when oxygen is involved in coordination. A significant portion of the process involved in the formation of a new type of compounds known
as macrocyclic ligands is attributed to condensation reactions between carbonyl compounds and primary amines. Macrocycles can be synthesized through conventional methods or through an in- situ process that involves the cyclization facilitated by the presence of metal ions in the reaction mixture.
The synthesis of an organic macrocycle in the absence of a metal ion often results in a low yield due to competing linear polymerization reactions that can dominate the cyclization process. Traditionally, the yield of cyclized product can be improved by performing the ring closing step at high dilution. However, the addition of a metal ion during or before this step can significantly enhance the yield of the desired macrocycle as its metal complex. In such cases, the improved yield is a result of one or more effects exerted by the metal ion, collectively known as the coordination template effect. Complexes of metal ions with synthetic macrocycles are of great importance, partly due to their resemblance to natural systems like porphyrins and cobalamins. The publication of several reviews covering various aspects of synthetic macrocyclic ligands underscores their significant importance. These ligands are of theoretical interest as they can create an environment with controlled geometry and ligand field strength. The development of multidentate ligands has enabled the synthesis of coordination compounds with coordination numbers ranging from four to ten.