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

Answer 1

Role of coordination compounds in biological systems
- Haemoglobin, the oxygen carrier in blood, is a complex of $F{e}^{2+}$ with porphyrin.
- The pigment chlorophyll in plants, responsible for photosynthesis, is a complex of $M{g}^{2+}$ with porphyrin.
- Vitamin $B_{12}$ (cyanocobalamine) the antipernicious anaemia factor, is a complex of cobalt.

(a) The platinum complex cis-$\left[Pt\right(N{H}_3{)}_{2}C{l}_2]$ (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 $C{u}^{2+}$ is based on the formation of a boue tetraammine copper (II) ion.
$C{u}^{2+}+4N{H}_3\to \underset{Deepblue}{\left[Cu\right(N{H}_3{)}_4{]}^{2+}}$
II. $N{i}^{2+}$ is detected by the formation of a red complex with dimethyl glyoxime (DMG).
$\begin{array}{c}NiC{l}_2+2DMG+2N{H}_{4}OH\to \underset{Nickelbisdimethy!glyoximate}{\left[Ni\right(DMG{)}_2]}+2N{H}_{4}Cl+2H_{2}O\end{array}$
III. The separation of $A{g}^{+}$ and $H{g}^{2+}$ in group I is based on the act that while AgCl dissolves in $N{H}_3$, forming a soluble complex, $H{g}_{2}C{l}_2$ forms an insoluble black substance.
$AgCl\left(s\right)+2N{H}_3\left(aq\right)\to \underset{Solublecomplex}{\left[Ag\right(N{H}_3{)}_2\left]Cl\right(aq)}$

$H{g}_{2}C{l}_2\left(s\right)+N{H}_3\to \underset{Blackinsolublesubstance}{Hg\left(N{H}_2\right)Cl.Hg+C{l}^{-}}$
Quantitative analysis Gravimetric estimation of $N{i}^{2+}$ is carried out by precipitating $N{i}^{2+}$ as red nickel dimethyl glyoxime complex in the presence of ammonia.
$N{i}^{2+}+2DMG\stackrel{N{H}_3}{\to }\underset{Redppt}{\left[Ni\right(DMG{)}_2]}$
EDTA is used in the complexometric determination of several metal ions such as $C{a}^{2+},Z{n}^{2+},F{e}^{2+},C{o}^{2+},N{i}^{2+},etc.$

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.
$\begin{array}{c}4Au+8KCN+2H_{2}O+O_2\to \underset{Potassiumdicyanoaurate\left(I\right)}{4K\left[Au\right(CN{)}_2]+4KOH}\\ 2K\left[Au\right(CN{)}_2]+Zn\to K_2[Zn\left(CN{)}_4\right]+2Au\downarrow \end{array}$
Purification of some metals can be achieved through complex formation. For example in Mond Process, impure mickel is coverted into $\left[Ni\right(CO{)}_4]$, which is decomposed to yield pure nickel.