Question

The IUPAC name of the complex shown below is \( \text{K}_3[\text{Co}(\text{ox})_3] \):

• A. Trispotassium trioxalatocobaltate (III)
• B. Potassium trioxalate cobaltate(III)
• C. Potassium trioxalatecobalt(III)
• D. Potassium trioxalatocobaltate(III)

Hint:

To eliminate options in coordination nomenclature questions instantly, always check the suffix of the metal! If the complex is preceded by an active metal counter-ion (like \(\text{K}\), \(\text{Na}\)), the complex sphere is guaranteed to be an anion, meaning the metal name must end in -ate!

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
IUPAC naming of coordination complexes follows a strict order: cation followed by anion.
Inside the complex sphere, ligands are named first (alphabetically), then the central metal.
If the complex ion is an anion, the metal name must end with the suffix "-ate".
The oxidation state of the metal is indicated in Roman numerals in parentheses.
Detailed Explanation:
1. Identify Cation and Anion: The complex dissociates as \(3K^+ + [Co(ox)_3]^{3-}\). The cation is Potassium. No prefix (like 'tri') is used for simple counter-ions outside the sphere.
2. Calculate Oxidation State of Co:
Let it be \(x\). Oxalate (\(ox\)) is a bidentate ligand with a charge of -2.
\(x + 3(-2) = -3 \implies x - 6 = -3 \implies x = +3\).
So, the oxidation state is III.
3. Naming the Anionic Sphere:
Ligand: 3 oxalates \(\implies\) trioxalato.
Metal: Cobalt becomes Cobaltate (because the sphere is an anion).
Assembling: Potassium trioxalatocobaltate(III).
Step 3: Final Answer:
The correct IUPAC name is Potassium trioxalatocobaltate(III).