Question

In the complex $\left[{\left(CoCl\right)}_2{\left(en\right)}_2\right]Br$ , the co-ordination number and oxidation state of cobalt are:

• A. $6$ and $+3$
• B. $3$ and $+3$
• C. $4$ and $+2$
• D. $6$ and $+1$

Answer 1

Answer: (A)

The given complex dissociate as follows:
$\left[{\left(CoCl\right)}_2{\left(en\right)}_2\right]Br\to {\left[{\left(CoCl\right)}_2{\left(en\right)}_2\right]}^{+}+{\left(Br\right)}^{-}$
Let $x$ be the oxidation state of cobalt in ${\left[{\left(CoCl\right)}_2{\left(en\right)}_2\right]}^{+}$ .
So, $x+2\left(-1\right)+0=+1x=+3$ .
As there are six $\sigma$ bonds between cobalt and the ligands, its coordination number is $6$ (here $\_{}^{{}^{\prime }}e{n}_{}^{{}^{\prime }}$ is a bidentate ligand).