What is the formula for the Tetraammineaquachloridocobalt (III) chloride coordination compound?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → $[Co(NH_3)_4(H_2O)Cl]Cl_2$
In coordination compounds, the name inside the brackets tells us the ligands directly bonded to the metal ion, and the last word (outside "chloride") indicates counter-ions outside the coordination sphere.
Breaking the name: Tetraammineaquachloridocobalt(III)
- Cobalt(III) $\rightarrow$ metal ion is $Co^{3+}$.
- Tetraammine $\rightarrow$ $4 \, NH_3$ ligands (neutral).
- Aqua $\rightarrow$ $1 \, H_2O$ ligand (neutral).
- Chlorido $\rightarrow$ $1 \, Cl^-$ ligand (inside coordination sphere).
Total ligand charge inside complex:
$NH_3 (0) + H_2O (0) + Cl^- (-1)$
So, charge on complex ion:
$Co^{3+} + (-1) = +2$
Complex ion = $[Co(NH_3)_4(H_2O)Cl]^{2+}$
Final word: chloride
This means chloride ions are present outside the coordination sphere as counter ions.
To balance $+2$ charge $\rightarrow$ need $2 \text{ Cl}^-$
$[Co(NH_3)_4(H_2O)Cl]Cl_2$
Why other options are incorrect
Option 2: has two aqua ligands and no coordinated chloride $\rightarrow$ does not match the name.
Option 3: has two coordinated chlorides, but name mentions only one chlorido.
Option 4: shows two chlorides inside and water outside $\rightarrow$ wrong ligand positions.