Question

Write the IUPAC name of the given complex :

\( \mathrm{[Co(NH_3)_4(H_2O)Cl]Cl_2} \)

Hint:

Find Co as +3 from the +2 charge of the complex ion, then name ligands alphabetically as ammine, aqua and chlorido.

Answer 1

Step 1: Read the formula:
The part inside the square brackets is the complex ion. The two \( \mathrm{Cl^-} \) ions outside the bracket are counter ions.
The central metal is cobalt. It holds four \( \mathrm{NH_3} \), one \( \mathrm{H_2O} \) and one \( \mathrm{Cl^-} \) as ligands.

Step 2: Find the oxidation state of cobalt:
Two chloride ions outside balance the charge, so the complex ion carries a charge of +2.
\( \mathrm{NH_3} \) and \( \mathrm{H_2O} \) are neutral and the bound chloride is -1. Let the oxidation state of Co be x.
\[ x + 4(0) + 1(0) + 1(-1) = +2 \]
\[ x = +3 \]

Step 3: Name the ligands in alphabetical order:
\( \mathrm{NH_3} \) is called ammine. There are four, so we write tetraammine.
\( \mathrm{H_2O} \) is called aqua.
\( \mathrm{Cl^-} \) is called chlorido.
The order is ammine, aqua, chlorido. The prefix tetra is ignored while sorting.

Step 4: Join the pieces:
Write the ligand names first, then the metal with its oxidation state in Roman numerals.
The complex ion is a cation, so the metal keeps the name cobalt.
The counter ion is named last as a separate word, chloride.

Final Answer:
The IUPAC name is tetraammineaquachloridocobalt(III) chloride.
\[ \boxed{\text{Tetraammineaquachloridocobalt(III) chloride}} \]