Question

Which of the following is correct?

• A. Ruby is \( Al_2O_3 \) containing 5\% \( Cr^{3+} \) ions
• B. \( Mn_2(CO)_{10} \) contains two bridged carbonyl groups
• C. \( [Co(NH_3)_6]^{3+} \) is an inner orbital complex whereas \( [Ni(NH_3)_6]^{3+} \) is an outer orbital complex
• D. \( [Ni(CN)_4]^{2-} \), \( [NiCl_4]^{2-} \) both have tetrahedral geometry

Hint:

- Inner Orbital Complexes: Use low spin configuration and involve inner d-orbitals.
- Outer Orbital Complexes: Use high spin configuration and involve outer d-orbitals.
- Strong Field Ligands (e.g., CN, NH3) often lead to low spin and inner orbital hybridization.

Answer 1

The Correct Option is C

Step 1: Understanding Inner and Outer Orbital Complexes 
- In coordination chemistry, inner and outer orbital complexes refer to hybridization of central metal ions in coordination compounds. 
- Inner orbital complex: The central metal ion utilizes inner d-orbitals for hybridization. 
- Outer orbital complex: The central metal ion utilizes outer d-orbitals for hybridization. 

Step 2: Analysis of \( [Co(NH_3)_6]^{3+ \) and \( [Ni(NH_3)_6]^{3+} \)} 
- \( [Co(NH_3)_6]^{3+} \): 
- \( Co^{3+} \) has an electronic configuration \( d^6 \). 
- With strong ligand \( NH_3 \), it forms low spin inner orbital complex (hybridization: \( d^2sp^3 \)). 
- \( [Ni(NH_3)_6]^{3+} \): 
- \( Ni^{3+} \) has an electronic configuration \( d^7 \). 
- It forms an outer orbital complex (hybridization: \( sp^3d^2 \)). 

Step 3: Verifying Other Options 
- Option (1) \( Al_2O_3 \) with 5\% \( Cr^{3+} \) is incorrect because Ruby is \( Al_2O_3 \) with trace amounts of \( Cr^{3+} \), but not exactly 5\%. 
- Option (2) \( Mn_2(CO)_{10} \) does not contain two bridged carbonyl groups, so it's incorrect. 
- Option (4) \( [Ni(CN)_4]^{2-} \) and \( [NiCl_4]^{2-} \) do not both have tetrahedral geometry. 
- \( [Ni(CN)_4]^{2-} \) is square planar due to strong field ligand \( CN^- \). 
- \( [NiCl_4]^{2-} \) is tetrahedral due to weak field ligand \( Cl^- \). 

Step 4: Conclusion 
- The correct statement is Option (3): \( [Co(NH_3)_6]^{3+} \) is an inner orbital complex, whereas \( [Ni(NH_3)_6]^{3+} \) is an outer orbital complex.