Question

# When a coordination compound $CoC{{l}_{3}}.6N{{H}_{3}}$ is mixed with $AgN{{O}_{3}}$, 3 moles of $AgCl$ are precipitated per mole of the compound. Write: (a)- The structural formula of the complex(b)- IUPAC names of the complex.

Hint: When the central metal atom is linked to several ions or neutral atoms by a coordinate bond is called a coordination compound. In a coordination compound, some ions on the ionization sphere and some are in the coordination sphere.

Example: ${{K}_{4}}[Fe{{(CN)}_{6}}],{{[Ag{{(CN)}_{2}}]}^{-}}$ etc.
When a coordination compound $CoC{{l}_{3}}.6N{{H}_{3}}$ is mixed with $AgN{{O}_{3}}$, 3 moles of $AgCl$ are precipitated per mole of the compound, which means that all three chlorine atoms are present in the ionization sphere because they ionize when reacted and all the 6 ammonia molecules are within the coordination sphere.
So, its chemical reaction of the complex with $AgN{{O}_{3}}$will be:
$[Co{{(N{{H}_{3}})}_{6}}]C{{l}_{3}}+3AgN{{O}_{3}}\to {{[Co{{(N{{H}_{3}})}_{6}}]}^{3+}}+3N{{O}_{3}}^{-}+ 3AgCl\downarrow$
(a)- Hence, the structural formula of the complex is $[Co{{(N{{H}_{3}})}_{6}}]C{{l}_{3}}$
(b)- As we can see that there are 6 ammonia molecules in the sphere, So, we name it as hexammine. The word ‘hex’ means 6. Now the coordination sphere is positively charged since the chloride ions are there in the ionization sphere. There are 3 chloride ions present, and as we know, the ammonia molecules are electrically neutral, so the oxidation state of cobalt will be +3. We represent the oxidation state by writing it in the roman number beside the name of the central metal atom. So, here it will be cobalt (III). Combining all of these, the IUPAC name of the complex $[Co{{(N{{H}_{3}})}_{6}}]C{{l}_{3}}$ will be Hexammine cobalt (III) chloride.