Discuss briefly giving an example in each case the role of coordination compounds in:
 (i) biological systems (ii) medicinal chemistry and (iii) analytical chemistry (iv) extraction/metallurgy of metals.

(i) Biological systems
Several naturally occurring biologically important compounds are coordination compounds.
Thus, chlorophyll is a coordination compound containing Mg(II) ions. It is green pigment present in plants and is used in photosynthesis.
(ii) Medicinal chemistry
To remove metal poisoning, complexing agents are used, cis platin $[PtC{l}_2(N{H}_3{)}_2]$ is used in cancer chemotherapy.
(iii) Analytical chemistry
Complex formation is used in qualitative scheme of analysis. In group I analysis, silver ion is separated from the precipitate of $AgCl,H{g}_{2}C{l}_2$  and $PbC{l}_2$. Aqueous ammonia is added to the ppt. AgCl dissolves due to formation of soluble complex.
$AgCl+2N{H}_3\rightleftharpoons [Ag(N{H}_3{)}_2]Cl$
(iv) Extraction/metallurgy of metals
Metals such as gold and silver are extracted by complex formation technique. Cyanide process is used for extraction of silver and gold from its ore.
$A{g}_{2}S+4NaCN\to 2Na[Ag(CN{)}_2]+N{a}_{2}S$
$2Na[Ag(CN{)}_2]+Zn\to N{a}_2[Zn(CN{)}_4]+2Ag$