Question

Identify the neutral complex from the following.

• A. $\text{Na}_3[\text{AlF}_6]$
• B. $[\text{Co(NO}_2)_3(\text{NH}_3)_3]$
• C. $[\text{Cu(NH}_3)_4]^{2+}$
• D. $[\text{Fe(CN)}_6]^{4-}$

Hint:

A quick look at the chemical formulas reveals that option (B) is the only entry that completely lacks external counter-ions (like $\text{Na}^+$) or explicit ionic superscript charges (like $2+$ or $4-$), immediately revealing its neutral identity.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks us to look at the given coordination coordination structures and determine which complex possesses zero overall electrical charge inside or outside its primary coordination sphere.

Step 2: Detailed Explanation:
Coordination complexes are classified into categories based on the charge layout of their coordination spheres:

Anionic Complex: The coordination sphere carries a net negative charge, such as $[\text{AlF}_6]^{3-}$ in option (A) and $[\text{Fe(CN)}_6]^{4-}$ in option (D).

Cationic Complex: The coordination sphere carries a net positive charge, such as $[\text{Cu(NH}_3)_4]^{2+}$ in option (C).

Neutral Complex: The coordination sphere carries no net electrical charge and requires no external counter-ions to stabilize it.
Let's verify the net internal charge of $[\text{Co(NO}_2)_3(\text{NH}_3)_3]$:
Cobalt exists in a $+3$ oxidation state ($\text{Co}^{3+}$).
Nitro ligands are mono-anionic ($3 \times \text{NO}_2^- = -3$).
Ammine ligands are fully neutral ($3 \times \text{NH}_3 = 0$).
Combining these internal charges yields:
$$ \text{Net Charge} = (+3) + (-3) + (0) = 0 $$ Since the internal charges balance perfectly within the coordination square brackets, the complex is completely neutral.

Step 3: Final Answer: The correct neutral complex option is (B).