The correct IUPAC name of the complex `[Cr(NH_3)_5(NCS)][ZnCl_4]` is

Options

A. Pentaammine isothiocyanato chromium (III) tetrachloro zincate (II)
B. Pentaammine isothiocyanato chromium (IV) tetrachloro zincate (III)
C. Tetrachloro zincate (II) pentaammine isothiocyanato chromium (III)
D. Pentaammine tetrachloro zincate (II) isothiocyanato chromium (III)

Answer

To determine the correct IUPAC name of the complex \([Cr(NH_3)_5(NCS)][ZnCl_4]\), we can follow these steps:

### Step 1: Identify the oxidation state of the central metal atom (Cr)
1. Let the oxidation state of chromium (Cr) be \(X\).
2. The ligands present are five ammonia (\(NH_3\)) and one isothiocyanate (\(NCS\)).
3. Ammonia is a neutral ligand, so it contributes 0 to the oxidation state.
4. The isothiocyanate ligand (\(NCS\)) has a charge of -1.
5. The zinc complex \([ZnCl_4]\) has a charge of -2 (since each chloride ion \(Cl^-\) has a charge of -1 and there are four of them).
6. The overall charge of the complex is neutral (0).

Setting up the equation:
\[ X + 5(0) + (-1) + 2 = 0 \]
This simplifies to:
\[ X - 1 + 2 = 0 \implies X + 1 = 0 \implies X = +3 \]

### Step 2: Identify the cation and anion
1. The cation is \([Cr(NH_3)_5(NCS)]^{3+}\) and the anion is \([ZnCl_4]^{2-}\).
2. The cation is larger in size compared to the anion, so it is named first.

### Step 3: Naming the ligands
1. The ligands are named in alphabetical order regardless of their charge.
2. The ligand \(NH_3\) is called "ammine" and \(NCS\) is called "isothiocyanato".
3. Since there are five ammonia ligands, we use the prefix "penta".

Thus, the cation part is named:
\[ \text{pentamine isothiocyanato chromium(III)} \]

### Step 4: Naming the anion
1. The anion \([ZnCl_4]^{2-}\) is named "tetrachloro" followed by the metal name with the suffix "ate" because it is an anionic complex.
2. Zinc in this case is in the +2 oxidation state, so we denote it as "zincate".

Thus, the anion part is named:
\[ \text{tetrachloro zincate(II)} \]

### Step 5: Combine the names
Finally, we combine the names of the cation and anion:
\[ \text{pentamine isothiocyanato chromium(III) tetrachloro zincate(II)} \]

### Final Answer
The correct IUPAC name of the complex \([Cr(NH_3)_5(NCS)][ZnCl_4]\) is:
\[ \text{pentamine isothiocyanato chromium(III) tetrachloro zincate(II)} \]

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