Question

Identify anionic sphere complex from following.

• A. Hexaamminecobalt(III) chloride
• B. Potassium hexacyanoferrate(II)
• C. Tetraamminedichlorocobalt(III) ion
• D. Pentaamminechlorocobalt(III) sulphate

Hint:

To identify an anionic complex, determine the oxidation state of the central metal ion and the charges of the ligands. Summing these charges will give the overall charge of the complex. If the overall charge is negative, it's an anionic complex. Look for compounds where the metal-containing complex is paired with a cation (like Potassium) to balance the negative charge.

Answer 1

The Correct Option is A

Step 1: Define an anionic sphere complex. An anionic sphere complex is a coordination complex in which the complex ion carries a net negative charge. We need to identify the option whose coordination sphere itself is negatively charged.
Step 2: Analyze Option A: Hexaamminecobalt(III) chloride. The complex ion is: \[ [Co(NH_3)_6]^{3+} \] Cobalt is in +3 oxidation state and ammonia is a neutral ligand. Therefore, the complex ion has a positive charge. Hence, this is a cationic complex.
Step 3: Analyze Option B: Potassium hexacyanoferrate(II). The complex ion is: \[ [Fe(CN)_6]^{4-} \] Iron is in +2 oxidation state and each cyanide ligand carries -1 charge. \[ +2 + 6(-1) = -4 \] Thus, the complex ion has a net negative charge. Hence, this is an anionic complex.
Step 4: Analyze Option C: Tetraamminedichlorocobalt(III) ion. The complex ion is: \[ [Co(NH_3)_4Cl_2]^+ \] Charge calculation: \[ +3 + 2(-1) = +1 \] Thus, it is cationic.
Step 5: Analyze Option D: Pentaamminechlorocobalt(III) sulphate. The complex ion is: \[ [Co(NH_3)_5Cl]^{2+} \] Charge calculation: \[ +3 + (-1) = +2 \] Thus, it is cationic.
Step 6: Conclusion. Only Potassium hexacyanoferrate(II) contains a negatively charged complex ion: \[ [Fe(CN)_6]^{4-} \] Therefore, it is the anionic sphere complex.