Question

Explain \( [Co(NH_3)_6]^{3+} \) is an inner orbital complex whereas \( [Ni(NH_3)_6]^{2+} \) is an outer orbital complex. [At. No. Co = 27, Ni = 28]

Hint:

For inner orbital complexes, low-spin configurations are typical with \( d^2sp^3 \) hybridization. For outer orbital complexes, high-spin configurations are typical with \( sp^3d^2 \) hybridization.

Answer 1

Step 1: Orbital Complex Types. Inner orbital complexes utilize \( d \)-orbitals from the inner shell (e.g., \( 3d \)-orbitals in transition metals), leading to low-spin complexes. Outer orbital complexes use \( d \)-orbitals from the outer shell (e.g., \( 4d \)-orbitals for higher oxidation states), resulting in high-spin complexes.

Step 2: Hybridization of \( [Co(NH_3)_6]^{3+} \). Cobalt in \( +3 \) has a \( 3d^6 \) configuration. The complex \( [Co(NH_3)_6]^{3+} \) employs inner \( 3d \)-orbitals for ligand coordination, exhibiting \( 3d^2sp^3 \) hybridization, characteristic of an inner orbital complex.

Step 3: Hybridization of \( [Ni(NH_3)_6]^{2+} \). Nickel in \( +2 \) has a \( 3d^8 \) configuration. The complex \( [Ni(NH_3)_6]^{2+} \) uses outer \( 4d \)-orbitals for bonding, with \( sp^3d^2 \) hybridization, classifying it as an outer orbital complex. Therefore, \( [Co(NH_3)_6]^{3+} \) is an inner orbital complex, and \( [Ni(NH_3)_6]^{2+} \) is an outer orbital complex.