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.

Answer 1

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.

Complete answer:
Coordination compounds are the compounds in which the central metal atom is linked to several ions or neutral molecules by coordinate bond, i.e., by donation of lone pairs of electrons by these ions or neutral molecules to the central metal atom.
The donor atoms, molecules, or anions that donate a pair of an electron to the central metal atom are called the ligands. The metal atom or ion to which ligands are attached is called the central metal atom or ion.
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.

Note: In a coordination compound some ions are in an ionizable form that is present in the ionization sphere, i.e., they participate in a chemical reaction. Proper rules should be followed for naming the coordination compound.