Question:

The IUPAC name of the following complex is
\[ [Co(NH_2CH_2CH_2NH_2)_2Br_2]Br \]

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In coordination compounds, ligands inside the coordination sphere are named first, followed by the metal with oxidation state in Roman numerals, and then the counter ion. For repeated complex ligands like ethylene diamine, use prefixes such as \(bis\), \(tris\), etc.
Updated On: Jun 26, 2026
  • Bis(ethane-1,2-diamine) dibromido cobalt (III) bromide
  • Di(ethane-1,2-diamine) dibromido cobalt (III) bromide
  • Tribromido bis(ethane-1,2-diamine) cobalt (III)
  • Dibromido bis(ethylene diamine) cobalt (III) bromide
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The Correct Option is D

Solution and Explanation

Step 1: Identify the coordination entity.
The given complex is \[ [Co(NH_2CH_2CH_2NH_2)_2Br_2]Br \] The coordination sphere is \[ [Co(NH_2CH_2CH_2NH_2)_2Br_2]^+ \] and the counter ion outside the coordination sphere is \[ Br^- \]

Step 2: Identify the ligands.
The ligand \[ NH_2CH_2CH_2NH_2 \] is ethylene diamine, commonly written as \[ en \] It is a neutral bidentate ligand.
There are two ethylene diamine ligands, so the prefix used is \[ bis \] because ethylene diamine is a polydentate ligand.
There are also two bromide ligands inside the coordination sphere. These are named as \[ dibromido \]

Step 3: Find the oxidation state of cobalt.
Let the oxidation state of cobalt be \[ x \] Ethylene diamine is neutral, so its charge is \[ 0 \] Each bromido ligand has charge \[ -1 \] There are two bromido ligands, so total charge due to bromido ligands is \[ -2 \] The complex ion has charge \[ +1 \] Therefore, \[ x+0-2=+1 \] \[ x=+3 \] Thus, cobalt is in the \[ +3 \] oxidation state.

Step 4: Write the IUPAC name.
Ligands are named before the metal.
The anionic ligand bromido is written as \[ dibromido \] The neutral ligand ethylene diamine is written as \[ bis(ethylene diamine) \] The metal is cobalt with oxidation state \[ (III) \] The counter ion is bromide.
Therefore, the name is Dibromido bis(ethylene diamine) cobalt (III) bromide

Step 5: Final conclusion.
Hence, the IUPAC name of the complex is \[ \boxed{\text{Dibromido bis(ethylene diamine) cobalt (III) bromide}} \] Therefore, the correct option is \[ \boxed{(4)} \]
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