Step 1: Understanding the Concept:
Naming coordination compounds requires a systematic application of IUPAC rules:
1. The cation is named first, followed by the anion.
2. Within the coordination sphere (brackets), ligands are named first in alphabetical order.
3. Numerical prefixes (di-, tri-, tetra-, penta-) indicate the quantity of each ligand but do not affect alphabetical sorting.
4. The oxidation state of the central metal is shown in parentheses as a Roman numeral immediately after the metal's name.
Step 2: Detailed Explanation:
Let us break down the chemical formula \([Co(NH_3)_5(Cl)]Cl_2\):
1. Identify and Alphabetize Ligands:
The coordination sphere contains two types of ligands:
- \(NH_3\): This is a neutral ligand named ammine (note the double 'm'). There are 5 such molecules, so the prefix is penta.
- \(Cl^-\): This is an anionic ligand. Inside the bracket, it is named chlorido (or older 'chloro').
In alphabetical order, 'ammine' (a) comes before 'chlorido' (c).
Thus, the ligand part is: pentaamminechlorido.
2. Determine the Oxidation State of Cobalt (x):
The total charge of a neutral compound is zero.
Charge of \(NH_3 = 0\).
Charge of each \(Cl^- = -1\).
There is one chloride inside the bracket and two outside.
Equation: \( x + 5(0) + 1(-1) + 2(-1) = 0 \)
\( x - 1 - 2 = 0 \implies x = +3 \).
The metal is thus named cobalt(III).
3. Name the Counter Anion:
The chloride ions outside the bracket are simply named chloride. Note that we do not use prefixes like 'di' for the ions outside the coordination sphere.
4. Construct the Full Name:
Combining the parts: Cation (Pentaaminechloridocobalt(III)) + Anion (chloride).
Step 3: Final Answer:
Assembling the components yields "Pentaaminechloridocobalt(III) chloride".
Checking the options, (C) is the only one that uses the correct alphabetical order, correct spelling of 'ammine', and the correct oxidation state.