Question

The IUPAC name of \([Co(NH_3)_5ONO]Cl_2\) is:

• A. Pentaamminechloronitrito-O-cobalt(III) chloride
• B. Pentaamminenitrito-O-cobalt(III) chloride
• C. Pentaamminenitrito-N-cobalt(III) chloride
• D. Pentaammineoxonitrito-cobalt(III) chloride

Hint:

IUPAC Naming of Coordination Compounds.

• Ligands in alphabetical order: ammine, chloro, nitrito, etc.
• ONO$^-$ is nitrito-O, NO$_2^-$ through N is nitrito-N.
• Oxidation state is shown in Roman numerals.

Answer 1

The Correct Option is B

In the complex \([Co(NH_3)_5ONO]Cl_2\), the ligands and central metal are:

• 5 \( \mathrm{NH_3} \) groups → pentaammine.
• \( \mathrm{ONO} \) group → nitrito-O (oxygen-bonded form of \( \mathrm{NO_2^-} \)).
• Central metal: Co.
• Oxidation state: Co is in +3 (since \( \mathrm{Cl^-} \times 2 \) and ligands are neutral/anionic).

So, IUPAC name becomes: Pentaamminenitrito-O-cobalt(III) chloride.

Answer 2

Step 1: Identify the ligands and their names
The complex ion is \([Co(NH_3)_5ONO]^{2+}\). It contains five ammine (NH₃) ligands and one nitrito ligand. The nitrito ligand is bonded through oxygen, which is indicated by "ONO" in the formula.

Step 2: Naming the ligands
Ammine ligands are named as "ammine." Since there are five NH₃ ligands, we use the prefix "pentaammine."
The nitrito ligand bonded through oxygen is named "nitrito-O-". This specifies the binding atom of the ligand.

Step 3: Naming the metal and oxidation state
The central metal is cobalt. The oxidation state of cobalt here is +3 because each NH₃ ligand is neutral and the nitrito ligand is also neutral, and the complex ion has a 2+ charge balanced by two chloride ions (Cl⁻). So, cobalt is in +3 oxidation state.
The metal name is written as "cobalt(III)."

Step 4: Naming the anion
There are two chloride ions outside the coordination sphere, named as "chloride."

Step 5: Putting it all together
The correct IUPAC name is "Pentaamminenitrito-O-cobalt(III) chloride."