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Question

Discuss briefly giving an example in each case the role of coordination compounds in 
Biological systems

Medicinal chemistry

Analytical chemistry

Extraction/metallurgy of metals


Solution

Role of coordination compounds in biological systems
- Haemoglobin, the oxygen carrier in blood, is a complex of Fe2+ with porphyrin.
- The pigment chlorophyll in plants, responsible for photosynthesis, is a complex of Mg2+ with porphyrin.
- Vitamin B12 (cyanocobalamine) the antipernicious anaemia factor, is a complex of cobalt.

(a) The platinum complex cis-[Pt(NH3)2Cl2] (cis-platin)  is used on the treatment of cancer.
(b) EDTA complex of calcium is used in the treatment of lead poisoning. Ca-EDTA is a weak complex; when it is administered, calcium in the complex is replaced by the lead present in the body and is eliminated in the urine.
(c) The excess of copper and iron present in the animal system are removed by the chelating ligands D-penicillamine and desferroxime B via the formation of complexes.

Qualitative analysis
I. Detection of Cu2+ is based on the formation of a boue tetraammine copper (II) ion.
Cu2++4NH3[Cu(NH3)4]2+Deepblue
II. Ni2+ is detected by the formation of a red complex with dimethyl glyoxime (DMG).
NiCl2+2DMG+2NH4OH[Ni(DMG)2]Nickel bis dimethy! glyoximate     +2NH4Cl+2H2O
III. The separation of Ag+ and Hg2+ in group I is based on the act that while AgCl dissolves in NH3, forming a soluble complex, Hg2Cl2 forms an insoluble black substance.
AgCl(s)+2NH3(aq)[Ag(NH3)2]Cl(aq)Soluble complex

Hg2Cl2(s)+NH3Hg(NH2)Cl.Hg    +ClBlack insoluble substance
Quantitative analysis Gravimetric estimation of Ni2+ is carried out by precipitating Ni2+ as red nickel dimethyl glyoxime complex in the presence of ammonia.
Ni2++2DMGNH3[Ni(DMG)2]Red ppt
EDTA is used in the complexometric determination of several metal ions such as Ca2+,Zn2+,Fe2+,Co2+,Ni2+,etc.

Role of coordination compounds in extraction/metallurgy of metals Extraction of various metals from their ore involves complex formation. For example, silver and gold are extracted from their ore by forming cyanide complex.
4Au+8KCN+2H2O+O24K[Au(CN)2]+4KOHPotassium dicyanoaurate (I)         2K[Au(CN)2]+ZnK2[Zn(CN)4]+2Au
Purification of some metals can be achieved through complex formation. For example in Mond Process, impure mickel is coverted into [Ni(CO)4], which is decomposed to yield pure nickel.


Chemistry
NCERT Textbook
Standard XII

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