Question: The IUPAC name of \( \left[ {{\text{Co}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text...

Question

The IUPAC name of $\left[ {{\text{Co}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text{6}}}} \right]{\text{C}}{{\text{l}}_{\text{3}}}$ is ______:
(A) Hexammine chloro cobalt (III)
(B) Hexaammonium cobalt (III) chloride
(C) Hexamine cobalt (III) chloride
(D) Hexammine cobalt (III) chloride
(E) Chloro Hexamminecobalt (III)

Answer 1

Solution

To answer this question, you must recall the rules set for the nomenclature of coordination compounds given by the International Union of Pure and Applied Chemistry, i.e. IUPAC. The rules are set in such a way so that the name of each species is unique. The metal centre is the parent compound and the ligands are written as prefixes along with their coordinate number.

Complete step by step solution
The given compound is a coordination compound. For the naming of this compound, first we identify the coordination spheres or the cations and the anions. So, we can see that the compound is composed of a complex cation and three chloride ions. So we have, the cationic species as ${\left[ {{\text{Co}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text{6}}}} \right]^{{\text{3 + }}}}$ and the ionic species is ${\text{C}}{{\text{l}}^ - }$ .
Now we first name the coordination action. The amine ligand is named as ammine. Since there are six ligands attached to it we add the prefix Hexa-. So the representation for the ligands becomes hexamine. Now we have cobalt cation. The oxidation state or the charge on cobalt is $+ 3$ . We know that for a metal cation, we write the name of the metal as it is and write its oxidation state in a bracket.
We can write the name of the cationic part as hexamine cobalt (III) ion. The IUPAC name of the compound will be Hexammine cobalt (III) Chloride.
The correct answer is D.

Note
The coordination sphere consists of a central cobalt metal ion and there are six ammonia ligands attached to it. Ammonia is a neutral ligand and chloride ion carries a single negative charge. So to balance the charge on the three chloride ions the cobalt cation must carry a triple positive charge.