The correct IUPAC name of [Co(en)2Cl2]NO3 is: (en = ethane-1,2-diamine)

🧠 Same Three Filters, Different Counter-Ion

This is structurally identical to CORD-027 — only the counter-ion has changed from $\mathrm{Cl^-}$ to $\mathrm{NO_3^-}$. The filters are the same:

1. Modern stem → "chlorido", not "chloro".
2. Composite ligand name → "bis(ethane-1,2-diamine)", not "di-".
3. Alphabetical sort places "chlorido" before "ethane-1,2-diamine".

🗺️ Construct It

Ligands. 2 × chlorido → "dichlorido". 2 × en → "bis(ethane-1,2-diamine)".

Oxidation state of Co. $x + 2(-1) + 2(0) = +1 \Rightarrow x = +3$. So Co(III).

Counter-ion. $\mathrm{NO_3^-}$ → "nitrate".

Stitched: Dichloridobis(ethane-1,2-diamine)cobalt(III) nitrate — option (2).

⚡ The "en Naming" Cheat

Whenever en is in the formula, automatically:

• Use "bis(ethane-1,2-diamine)", never "di(en)" or "dien" (which is a different ligand!) or "di(ethylenediamine)".
• Place "ethane-1,2-diamine" after any ligand starting with letters a–d.

This single rule resolves most en-containing IUPAC questions.

⚠️ "Dien" Is a Different Ligand

"dien" = diethylenetriamine, a tridentate ligand. "en" = ethylenediamine, bidentate. Confusing the names is easy if you abbreviate carelessly. Always write out "ethane-1,2-diamine" or "(en)" with explicit parentheses.

$\boxed{\text{Answer: (2) Dichloridobis(ethane-1,2-diamine)cobalt(III) nitrate}}$