9.27 Discuss briefly giving an example in each case the role of coordination compounds in:

(i) biological systems                 (iii) analytical chemistry

(ii) medicinal chemistry and     (iv) extraction/metallurgy of metals.

(i) Role of coordination compounds in biological systems:
In a biological system, photosynthesis is made possible by the presence of chlorophyll pigment. This pigment is a coordination compound of magnesium. In the human biological system, several coordination compounds play important roles. For example, the oxygen-carrier of blood, i.e., haemoglobin, is a coordination compound of iron.

(ii) Role of coordination compounds in medicinal chemistry:
Certain coordination compounds of platinum (for example, cis-platin) are used for inhibiting the growth of tumours.
(iii) Role of coordination compounds in analytical chemistry:

During salt analysis, a number of metal ions are detected with the help of the colour changes they exhibit with different reagents. These colour changes are a result of the coordination compounds or complexes formation that the metal ion form with different ligands.

For example, the hardness of water is estimated by simple titration with Na2EDTA. The Ca2+ and Mg2+ ions form stable complexes with EDTA.

(iii) Role of coordination compounds in extraction or metallurgy of metals:

The process of extraction of some of the metals from their ores involves the formation of complexes. For example, in aqueous solution, gold combines with cyanide ions to form $\left[Au{\left(CN\right)}_{2}\right]$. From this solution, gold is later extracted by the addition of zinc metal.