Question

Consider the following complex compounds (A) \([Ni(NH_3)_6]^{2+}\) (B) \([NiCl_4]^{2-}\) (C) \([Ni(en)_3]^{2+}\) The number of unpaired electrons in A, B and C respectively and order of frequency of absorbed radiation among A, B and C is:

• A. \(2, 2, 2\) and \(C > A > B\)
• B. \(0, 2, 2\) and \(A > B > C\)
• C. \(2, 2, 0\) and \(A > C > B\)
• D. \(2, 2, 2\) and \(C > B > A\)

Answer 1

The Correct Option is A

Concept: Nickel in these complexes has oxidation state \(+2\). \[ Ni^{2+} : 3d^8 \] The number of unpaired electrons depends on ligand strength and geometry. 
Step 1: Analyse complex A \[ [Ni(NH_3)_6]^{2+} \] Octahedral complex. Electronic configuration in crystal field: \[ t_{2g}^{6} e_g^{2} \] Number of unpaired electrons: \[ n = 2 \] 
Step 2: Analyse complex B \[ [NiCl_4]^{2-} \] Weak field ligand \(Cl^-\) produces tetrahedral complex. Electronic configuration: \[ e^{4} t_2^{4} \] Number of unpaired electrons: \[ n = 2 \] 
Step 3: Analyse complex C \[ [Ni(en)_3]^{2+} \] Strong field ligand \(en\), octahedral complex. Configuration: \[ t_{2g}^{6} e_g^{2} \] Number of unpaired electrons: \[ n = 2 \] Thus for A, B, C: \[ 2,\,2,\,2 \] 
Step 4: Order of absorbed radiation Crystal field splitting depends on ligand strength. Ligand strength order: \[ en > NH_3 > Cl^- \] Higher splitting means higher frequency of absorbed radiation. \[ C > A > B \] Thus correct option: \[ \boxed{2,2,2 \text{ and } C > A > B} \]