Question

Sketch qualitatively crystal field d orbital energy level diagrams for each of the following complexes :

(a) [Ni(en)₃]²⁺ 

(b) [Mn(CN)₆]^3- 

(c) [Fe(H₂O)₆]²⁺ 

Predict whether each of the complexes is diamagnetic or paramagnetic.

Answer 1

(a) The complex ion, [Ni(en)₃]²⁺ is octahedral.

Since en is a strong ligand there is pairing of electrons. Number of unpaired electrons = n = 2 in t_2g, orbitals Magnetic moment \(=\mu = \sqrt{n(n + 2)}\)

\(=\sqrt{2(2 + 2)} = 2.83\) B.M.

The complex ion is paramagnetic.

(b) The complex ion [Mn(CN)₆]^3-  is octahedral.

Since CN^- is a strong ligand there is pairing of electrons. Number of unpaired electrons = n = 2 in t_2g, orbitals Magnetic moment \(=\mu = \sqrt{n(n+2)}\)

\(=\sqrt{2(2+2)}\) = 2.83 B.M.

The complex ion is paramagnetic.

(c) The complex ion [Fe(H₂O)₆]²⁺ is octahedral.

Since H₂O is a weak ligand, there is no pairing of electrons. Number of unpaired electrons = n = 4 in t_2g and e_g orbitals. Magnetic moment

The complex ion is paramagnetic.