Question

Indicate the coordination number for the central metal atom in each of the following coordination compounds:

\(\begin{aligned}{}(a)\left( {Pt{{\left( {{H_2}O} \right)}_2}B{r_2}} \right)\\(b)\left( {Pt\left( {N{H_3}} \right)(py)(Cl)(Br)} \right)\left( {py = } \right.pyridine,\left. {{C_5}{H_5}\;N} \right)\\(c)\left( {Zn{{\left( {N{H_3}} \right)}_2}C{l_2}} \right)\\(d)\left( {Zn\left( {N{H_3}} \right)(py)(Cl)(Br)} \right)\\(e)\left( {Ni{{\left( {{H_2}O} \right)}_4}C{l_2}} \right)\\(f){\left( {Fe{{(en)}_2}{{(CN)}_2}} \right)^ + }\left( {en = } \right.ethylenediamine,\left. {{C_2}{H_8}\;{N_2}} \right)\end{aligned}\)

Short answer

The number of ligands attached to the central metal ion attached through the secondary valencies and are present inside the coordination sphere is said to be the coordination number of central metal ion.

Step-by-step solution

Given information

We are asked to indicate the coordination number for the central metal atom in each of the following coordination compounds of\(\begin{aligned}{}(a)\left( {Pt{{\left( {{H_2}O} \right)}_2}B{r_2}} \right)\\(b)\left( {Pt\left( {N{H_3}} \right)(py)(Cl)(Br)} \right)\left( {py = } \right.pyridine,\left. {{C_5}{H_5}\;N} \right)\\(c)\left( {Zn{{\left( {N{H_3}} \right)}_2}C{l_2}} \right)\\(d)\left( {Zn\left( {N{H_3}} \right)(py)(Cl)(Br)} \right)\\(e)\left( {Ni{{\left( {{H_2}O} \right)}_4}C{l_2}} \right)\\(f){\left( {Fe{{(en)}_2}{{(CN)}_2}} \right)^ + }\left( {en = } \right.ethylenediamine,\left. {{C_2}{H_8}\;{N_2}} \right)\end{aligned}\)

Explanation

\((a)\left( {Pt{{\left( {{H_2}O} \right)}_2}B{r_2}} \right)\)

• In this,\({\bf{4}}\)monodentate ligands are present inside the coordination sphere, which clearly indicated that the coordination number of the central metal ion\({\bf{Pt}}\)is\({\bf{4}}\).

\((b)\left( {Pt\left( {N{H_3}} \right)(py)(Cl)(Br)} \right)\left( {py = } \right.pyridine,\left. {{C_5}{H_5}\;N} \right)\)

• Here also, we could see\({\bf{4}}\)monodentate ligands present inside the coordination sphere, which clearly indicated that the coordination number of the central metal ion\({\bf{Pt}}\)is\({\bf{4}}\).

\((c)\left( {Zn{{\left( {N{H_3}} \right)}_2}C{l_2}} \right)\)

• Here again, we could see\({\bf{4}}\)monodentate ligands present inside the coordination sphere, which clearly indicated that the coordination number of the central metal ion\(Zn\)is\({\bf{4}}\).

\((d)\left( {Zn\left( {N{H_3}} \right)(py)(Cl)(Br)} \right)\)

• Here also, we could see\({\bf{4}}\)monodentate ligands present inside the coordination sphere, which clearly indicated that the coordination number of the central metal ion\(Zn\)is\({\bf{4}}\).

\((e)\left( {Ni{{\left( {{H_2}O} \right)}_4}C{l_2}} \right)\)

• Here, We can see that\({\bf{6}}\)monodentate ligands are present inside the coordination sphere, which means the coordination number of the central metal ion\({\rm{Ni}}\)is\({\bf{6}}\).

\((f){\left( {Fe{{(en)}_2}{{(CN)}_2}} \right)^ + }\left( {en = } \right.ethylenediamine,\left. {{C_2}{H_8}\;{N_2}} \right)\)

• We can see that\({\bf{2}}\)monodentate\(\left( {C{N^ - }} \right)\)ligands and\({\bf{2}}\)bidentate\((en)\)ligands are present inside the coordination sphere, which shows that the coordination number of the central metal ion\({\bf{Fe}}\)is\({\bf{6}}\).
• Since\({\bf{2}}\)monodentate ligans donate\({\bf{2}}\)electrons and each of the bidentate donates\({\bf{2}}\)electrons and since we have\({\bf{2}}\)of them, they donate\({\bf{4}}\)electrons, and their sum is\({\bf{6}}\).

Result

\(\begin{aligned}{}a)Pt &= 4\\b){\rm{Pt}} &= 4\\c)Zn &= 4\\d)Zn &= 4\\e){\rm{Ni}} &= 6\\f){\rm{Fe}} &= 6\end{aligned}\)