Question

Number of N-Mn-Cl bonds [N-Mn bonds is cis to Mn-Cl bond] in cis $\left[\mathrm{Mn}{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]$ are

Answer 1

Step 1: Identifying the structure of cis $\mathbf{\left[}\mathbf{Mn}{\mathbf{\left(}\mathbf{en}\mathbf{\right)}}_{\mathbf{2}}{\mathbf{Cl}}_{\mathbf{2}}\mathbf{\right]}$

We know that (en) is Ethylenediamine $(\stackrel{..}{\mathrm{N}}{\mathrm{H}}_2-{\mathrm{CH}}_2-{\mathrm{CH}}_2-\stackrel{..}{\mathrm{N}}{\mathrm{H}}_2)$ and it is a bidentate ligand, that is it donates two electron pairs to a metal atom.

Now there are 2 possible structure for $\left[\mathrm{Mn}{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]$, one is cis $\left[\mathrm{Mn}{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]$ and the other one is trans $\left[\mathrm{Mn}{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]$

Step 2: Calculating the total number of cis $\mathbf{N}\mathbf{-}\mathbf{Mn}\mathbf{-}\mathbf{Cl}$ bonds

Now we can see that there are a total of 8 $\mathrm{N}-\mathrm{Mn}-\mathrm{Cl}$ as each Nitrogen has 2 $\mathrm{N}-\mathrm{Mn}-\mathrm{Cl}$ that are present in cis $\left[\mathrm{Mn}{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]$.

The 2 above every Nitrogen indicates that each Nitrogen atom has 2 $\mathrm{N}-\mathrm{Mn}-\mathrm{Cl}$ bonds.

Now out of this, we have to identify the cis bonds as per the given question.

Now it is given that N-Mn bonds is cis to Mn-Cl bond, so the trans bonds cannot be included in this.

Thus we can see from the cis figure that, there are 2 $\mathrm{N}-\mathrm{Mn}-\mathrm{Cl}$ bonds that are trans.

$\therefore$The total number of cis $\mathrm{N}-\mathrm{Mn}-\mathrm{Cl}$ bonds in cis $\left[\mathrm{Mn}{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2\right]$ are $8-2=6$