Question

Write the formula of ionisation isomer of $[Cr{({H_2}O)_4}B{r_2}]Cl$ .

Answer 1

Hint: In ionisation isomerism, there is an exchange of ions inside and outside the coordination sphere.Ionisation isomers are the compounds that have the same chemical formula but give different ions in the solution.

Complete step by step answer:
Ionisation isomers are the compounds that produce different ions in solution, that is they have ions interchanged inside and outside the coordination sphere. The central ion and the other ligands are identical.
In the given coordination compound, $[Cr{({H_2}O)_4}B{r_2}]Cl$ , both Br and Cl have the nobility to act as a ligand and the exchange of these two ions will result in a different isomer $[Cr{({H_2}O)_4}BrCl]Br$ . In solution, the first compound will give $C{l^ - }$ ions and the latter will give $B{r^ - }$ ions and hence, both these compounds are called ionisation isomers.
The formula for the ionisation isomer of $[Cr{({H_2}O)_4}B{r_2}]Cl$ is $[Cr{({H_2}O)_4}BrCl]Br$ .
One isomer $[Cr{({H_2}O)_4}B{r_2}]Cl \to C{l^ - }$ in solution
Another isomer $[Cr{({H_2}O)_4}BrCl]Br \to B{r^ - }$ in solution
In $[Cr{({H_2}O)_4}B{r_2}]Cl$ , the two bromides are inside the coordination sphere and the chloride ion outside the coordination sphere. In the latter, one of the bromide ions changes position with chloride ion and then chloride ion occurs within the coordination sphere, and one the bromide ion is outside it.

Note:
Ionisation isomers are identical except for a ligand that has exchanged places with an anion or neutral molecule that was originally outside the coordination complex. Ionisation isomerism arises when an ionisable counter ion (simple ion) itself can act as a ligand. The exchange of such counter ions with one or more ligands in the coordination entity will result in ionisation isomers. These isomers will give different ions in the solution.