Question

Which of the following is diamagnetic in nature?

• A. $ Co^{3+}$ , octahedral complex with weak field ligands
• B. $ Co^{3+} $ , octahedral complex with strong field ligands
• C. $ Co^{2+} $ in tetrahedral complex
• D. $ Co^{2+} $ in square planar complex

Answer 1

Answer: (B)

$Co ^{3+}=[ Ar ] 3 d^{6} 4 s^{0}$ In the presence of strong field ligands, pairing occurs.
Thus, $Co ^{3+}$ (in presence $=[ Ar ]$
of strong (no unpaired electrons) field ligand) Thus, it is diamagnetic in nature.
(Note: $Co ^{2+}$ always contains an unpaired electron.)