Question

Identify the anionic sphere complex from following.

• A. Triamminetrinitrocobalt(III)
• B. Tetramminecopper(II) ion
• C. Sodium hexanitrocobaltate(III)
• D. Pentacarbonyliron(0)

Hint:

The complex is anionic when the charge on the coordination sphere is negative.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
A complex is called anionic when the charge on the coordination sphere (the part in square brackets) is negative.
The counter ion is then a cation.

Step 2: Check each complex
Triamminetrinitrocobalt(III), \([\text{Co}(\text{NH}_{3})_{3}(\text{NO}_{2})_{3}]\), is neutral.
Tetramminecopper(II) ion, \([\text{Cu}(\text{NH}_{3})_{4}]^{2+}\), is cationic.
Pentacarbonyliron(0), \([\text{Fe}(\text{CO})_{5}]\), is neutral.

Step 3: Sodium hexanitrocobaltate(III)
Its formula is \(\text{Na}_{3}[\text{Co}(\text{NO}_{2})_{6}]\).
The sphere has charge \(+3-6=-3\), balanced by three \(\text{Na}^{+}\) ions.

Final Answer:
Sodium hexanitrocobaltate(III) has an anionic coordination sphere. \[ \boxed{\text{(C) }\text{Sodium hexanitrocobaltate(III)}} \]