As per IUPAC nomenclature, the name of the complex, `[Co(H_2O)_4(NH_3)_2]Cl_3` is

Options

A. Tetraaquadiaminecobalt (III) chloride
B. Tetraaquadiamminecobalt (III) chloride
C. Diaminetetraaquacobalt (III) chloride
D. Diamminetetraaquacobalt (III) chloride

Answer

To determine the IUPAC name of the complex `[Co(H_2O)_4(NH_3)_2]Cl_3`, we can follow these steps:

### Step 1: Determine the oxidation state of cobalt
The complex has the formula `[Co(H_2O)_4(NH_3)_2]Cl_3`.

- Water (H₂O) and ammonia (NH₃) are neutral ligands, so their contributions to the charge are zero.
- The three chloride ions (Cl⁻) contribute a total charge of -3.

Let the oxidation state of cobalt be \( x \). The overall charge of the complex must be zero, so we can set up the equation:

\[ x + 0 + 0 - 3 = 0 \]

This simplifies to:

\[ x - 3 = 0 \]

Thus,

\[ x = +3 \]

So, cobalt has an oxidation state of +3.

### Step 2: Identify the ligands and their names
- The complex contains 4 water molecules (H₂O) and 2 ammonia molecules (NH₃).
- According to IUPAC nomenclature:
- Water is referred to as "aqua".
- Ammonia is referred to as "ammine".

### Step 3: Count the number of each type of ligand
- There are 4 aqua ligands, which is denoted as "tetra".
- There are 2 ammine ligands, which is denoted as "di".

### Step 4: Write the name of the complex
When naming the complex, we list the ligands in alphabetical order, regardless of their quantity.

- The ligands are "ammine" and "aqua".
- Alphabetically, "ammine" comes before "aqua".

Thus, we write:
- "diammine" for the 2 ammine ligands.
- "tetraaqua" for the 4 aqua ligands.

### Step 5: Combine the ligands with the metal and its oxidation state
- The name of the metal is "cobalt".
- Since cobalt has an oxidation state of +3, we denote this as "cobalt(III)".

### Step 6: Add the counter ions
- The complex has 3 chloride ions, which are simply referred to as "chloride".

### Final Name
Putting it all together, the full IUPAC name of the complex is:

**diammine tetraaquacobalt(III) chloride**