Question

Write the IUPAC names of the following compounds:
i. $\left[ {Co{{\left( {N{H_3}} \right)}_5}{{\left( {ONO} \right)}_2}} \right]Cl$
ii. ${K_3}\left[ {Cr{{\left( {CN} \right)}_6}} \right]$
A.Pentaamminenitritocobalt (III) chloride
Potassium Hexacyanochromate (III)
B.Pentaamminenitritocobalt (II) chloride
Potassium Hexacyanide Chromate (III)
C.Pentaamminenitritocobalt (III) chloride
Potassium Hexacyanochromate (III)
D.PentaamminenitroCobalt (II) Chloride
Potassium Hexacyanochromate (III)

Answer 1

Hint: The naming of the coordination compounds is done on the basis of the IUPAC nomenclature of the coordination compound. In the complex, the ligands come first in alphabetical order followed by the metal with its oxidation number.

Complete step by step answer:
In the first compound, there are two types of ligands, one to satisfy the coordination sphere of the cobalt ion and the other to satisfy the primary charge on it. The secondary charge or the coordination sphere is satisfied by the ammonia molecules while the nitrito group, bonded to the cobalt ion through the oxygen atom and the chloride group satisfies the primary charge. As the formal charge of nitrite is $\left( { - 1} \right)$ and there are two nitrite group and one chloride group with charge $\left( { - 1} \right)$ , so the formal charge on the cobalt cation should be $\left( { + 3} \right)$.
The nomenclature of the compound is: Pentaamminenitritocobalt (III) chloride.
In the second compound, the formal charge on the cyanide group is $\left( { - 1} \right)$ and as there are six cyano groups the residual charge on the chromium complex should be $\left( { - 3} \right)$ because the charge on chromium is $\left( { + 3} \right)$. So three potassium ions to satisfy the negative ions on the complex anion.
Hence, the name of the compound is: Potassium Hexacyanochromate (III).

So, the correct option is option C.

Note:
As per IUPAC recommendations, the naming of a complex is done on the basis of the alphabetical order and when the coordination theory was developed coordination compounds were considered to be formed from independently stable compounds. they were therefore named on the basis of independently additive principles.