(i) Coordination compounds are of great importance in biologicalsystems. The pigment responsible for photosynthesis, chlorophyll, is acoordination compound of magnesium. Haemoglobin, the red pigmentof blood which acts as oxygen carrier is a coordination compound ofiron. Vitamin B12, cyanocobalamine, the anti- pernicious anaemia factor,is a coordination compound of cobalt. Among the other compounds ofbiological importance with coordinated metal ions are the enzymeslike, carboxypeptidase A and carbonic anhydrase (catalysts of biologicalsystems).
(ii) There is growing Interest in the use of chelate therapy in medicinalchemistry. An example is the treatment of problems caused by the presenceof metals in toxic proportions in plant/animal systems. Thus, excess ofcopper and iron are removed by the chelating ligands D-penicillamineand desferrioxime B via the formation of coordination compounds. EDTAis used in the treatment of lead poisoning. Some coordination compoundsof platinum effectively inhibit the growth of tumours. Examples are: cis-platin and related compounds.
(iii) Coordination compounds find use in many qualitative and quantitativechemical analysis. The familiar colour reactions given by metal ions witha number of ligands (especially chelating ligands), as a result of formationof coordination entities, form the basis for their detection and estimationby classical and instrumental methods of analysis. Examples of suchreagents include EDTA, DMG (dimethylglyoxime), a-nitroso-b-naphthol,cupron, etc.
(iv) Some important extraction processes of metals, like those of silver andgold, make use of complex formation. Gold, for example, combines withcyanide in the presence of oxygen and water to form the coordinationentity [Au(CN)2]–in aqueous solution. Gold can be separated in metallicform from this solution by the addition of zinc.