Macrocyclic Ligand Design. A Large Covalently-Linked Ring System Incorporating Four Cyclam Units and its Interaction with Nickel(II), Copper(II), Zinc(II), and Cadmium(II)

Abstract

A cyclic, tetra-linked macrocyclic species incorporating four 1,4,8,11-tetraazacyclotetradecane (cyclam) subunits has been synthesized employing Boc amine-group protecting chemistry coupled with high dilution conditions for the cyclization step. A series of 4:1 (metal:ligand (M:L)) complexes with nickel(ii), copper(ii), zinc(ii), and cadmium(ii) has been synthesized. Visible spectophotometric (including spectrophotometric titration), EPR, NMR, and electrochemical studies are reported for individual complexes and are in general accord with similar 4:1 (M:L) coordination behaviour occurring in both the solid state and in solution. The study makes available an example of a new category of large cyclic receptors whose cavity can be tuned electronically through variation of the metal centres incorporated in the cavity walls.