Question

IUPAC name \( [\text{CoCl}_2(\text{en})_2]\text{Cl} \)

Hint:

Remember to use "bis", "tris", etc., for ligands whose names already contain numerical prefixes like "di" or "tri" (e.g., ethylenediamine, triphenylphosphine) to avoid confusion.

Answer 1

Step 1: Understanding the Concept:
Naming coordination compounds requires following IUPAC rules: name the cation first, then the anion. Inside the complex ion, list ligands alphabetically, followed by the metal and its oxidation state in Roman numerals.

Step 2: Key Formula or Approach:
1. Identify the complex ion and counter ion.
2. Identify and name the ligands, determining their alphabetical order.
3. Use appropriate prefixes for the number of ligands (di-, tri- or bis-, tris- for complex ligands).
4. Calculate the oxidation state of the central metal.

Step 3: Detailed Explanation:
Let's break down the formula $[\text{CoCl}_2(\text{en})_2]\text{Cl}$:
- The cation is the complex ion $[\text{CoCl}_2(\text{en})_2]^+$.
- The anion is chloride ($\text{Cl}^-$).
- Ligands:
- '$\text{Cl}$' represents chloride. As a ligand, it is named 'chlorido'. There are two, so we use the prefix 'di-' $\rightarrow$ dichlorido.
- '$\text{en}$' represents ethylenediamine. Its systematic IUPAC name is 'ethane-1,2-diamine'. Since the ligand name contains a number/prefix, we use 'bis-' for two of them $\rightarrow$ bis(ethane-1,2-diamine).
- Alphabetical order: 'chlorido' comes before 'ethane-1,2-diamine'.
- Central Metal: Cobalt (Co). Since the complex is a cation, the name remains 'cobalt'.
- Oxidation State:
Let the oxidation state of Co be $x$.
Charge of chlorido ligand = $-1$
Charge of 'en' ligand = $0$ (neutral)
Overall charge of the complex cation $= +1$ (to balance the one $\text{Cl}^-$ anion outside).
$x + 2(-1) + 2(0) = +1$
$x - 2 = +1 \implies x = +3$
The oxidation state is (III).
Assembling the name: dichloridobis(ethane-1,2-diamine)cobalt(III) chloride.

Step 4: Final Answer:
The IUPAC name is dichloridobis(ethane-1,2-diamine)cobalt(III) chloride.