(a) Define didentate ligand. Give an example.
(b) Indicate the type of isomerism exhibited by the given complex :
\( \mathrm{[Pt(NH_3)(H_2O)Cl_2]} \)
(a) Define didentate ligand. Give an example.
(b) Indicate the type of isomerism exhibited by the given complex :
\( \mathrm{[Pt(NH_3)(H_2O)Cl_2]} \)
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Solution and Explanation
Part (a) asks for a definition and an example of a didentate ligand.
Part (b) asks for the kind of isomerism in a platinum complex.
Step 2: Part (a) - define the ligand.
A ligand is an ion or molecule that donates a lone pair to the central metal.
A didentate ligand has two donor atoms.
It binds to the same metal ion through both donor atoms.
This forms a ring with the metal, called a chelate ring.
Step 3: Part (a) - give an example.
Ethane-1,2-diamine (en) is a didentate ligand.
\[ \mathrm{H_2N{-}CH_2{-}CH_2{-}NH_2} \]
Each nitrogen atom has a lone pair and both bind to the metal.
Oxalate ion, \(\mathrm{C_2O_4^{2-}}\), is another example.
Step 4: Part (b) - find the geometry.
The two chloride ions are -1 each, and the other two ligands are neutral.
So platinum is in the +2 state, with the configuration \(\mathrm{5d^8}\).
Pt(II) with four ligands forms a square planar complex.
Step 5: Part (b) - decide the isomerism.
The complex has the type \(\mathrm{[M\,a_2\,b\,c]}\), where a = Cl, b = \(\mathrm{NH_3}\) and c = \(\mathrm{H_2O}\).
The two Cl ligands can sit next to each other (cis) or opposite each other (trans).
These two arrangements are different compounds with the same formula.
So the complex shows geometrical (cis-trans) isomerism.
It does not show optical isomerism because the square plane is a mirror plane.
Final Answer:
(a) A didentate ligand has two donor atoms and forms a chelate ring, for example ethane-1,2-diamine (en).
(b) \(\mathrm{[Pt(NH_3)(H_2O)Cl_2]}\) shows geometrical isomerism (cis and trans forms).
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