The IUPAC name for `[Co(NCS)(NH_3)_5]Cl_2`is-

Options

A. Pentaammine (thiocyanato-N) cobalt (III) chloride
B. Pentaammine (thiocyanato-S) cobalt (III) chloride
C. Pentaamine (isothiocyanato-N,S) cobalt (III) chlvaoride
D. Pentaammine (mercapto-N) cobalt (III) chloride

Answer

To determine the IUPAC name for the coordination compound `[Co(NCS)(NH_3)_5]Cl_2`, we will follow these steps:

### Step 1: Identify the Cation and Anion
The coordination compound consists of a cationic part and an anionic part. The cation is `[Co(NCS)(NH_3)_5]` and the anion is `Cl_2`.

### Step 2: Determine the Oxidation State of Cobalt
Let the oxidation state of cobalt be \( x \).
- The thiocyanate ion (NCS) has a charge of -1.
- The ammonia (NH₃) is a neutral ligand.

The overall charge of the cation is +2 (since there are two chloride ions, each with a -1 charge).

Thus, we can set up the equation:
\[ x + (-1) + 0 = +2 \]
\[ x - 1 = 2 \]
\[ x = +3 \]

So, the oxidation state of cobalt is +3.

### Step 3: Naming the Ligands
- The ligand NCS is called thiocyanate. Since it has a negative charge, we will use the prefix "thio" and denote the donor atom as nitrogen (N), making it "thiocyanato-N".
- The ligand NH₃ is called ammine. Since there are five NH₃ ligands, we will use the prefix "penta", resulting in "pentaammine".

### Step 4: Arranging the Ligands Alphabetically
When naming the ligands, we arrange them in alphabetical order based on their names, not the prefixes:
1. "ammine" (from pentaammine)
2. "thiocyanato-N"

Thus, we write "pentaammine" first followed by "thiocyanato-N".

### Step 5: Naming the Central Metal Atom
The central metal atom is cobalt, and since its oxidation state is +3, we denote it as "cobalt(III)".

### Step 6: Naming the Anion
The anion is chloride (Cl⁻). Since there are two chloride ions, we write "dichloride".

### Step 7: Combining All Parts
Now, we combine all parts to form the complete IUPAC name:
- Cation: "pentaammine thiocyanato-N cobalt(III)"
- Anion: "dichloride"

Putting it all together, the full IUPAC name is:
**Pentaammine thiocyanato-N cobalt(III) dichloride.**

### Final Answer
The IUPAC name for `[Co(NCS)(NH_3)_5]Cl_2` is **Pentaammine thiocyanato-N cobalt(III) dichloride.**

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