Macrocyclic ligands that can incorporate two or more metal ions giving homo- or hetero-dinuclear complexes are of considerable interest. Some of these hetero-dinuclear complexes are interesting as they mimic the active sites of metalloenzymes, such as cytochrome-c oxidase and bovine erythrocyte superoxide dismutase. Such systems are very helpful in investigating mutual influences of the two metal centers on electronic, magnetic, and electrochemical properties. Therefore, such types of system are very helpful in biological diagnostic applications. Research in inorganic chemistry has expanded in recent years by exploiting a variety of chelating ligands to modify and control the characteristics of metal ions in biological systems. Macrocyclic ligands offer the benefit of high stability complex formation and, through functionalization, the opportunity to modify the coordination environment. The pharmaceutical and bio-medical industry has yet to appreciate the impact coordination chemistry can have on the design of novel medicines. This may change the future as skilled multi-disciplinary experts may develop their investigation using a strategic approach to complex design.