Predict the magnetic nature of A and B. (a) Both are diamagnetic

Question

The coordination number of Ni²⁺ is 4. 

NiCl₂ + KCN (excess) → A (cyano complex) 

NiCl₂ + conc. HCI (excess) → B (chloro complex)

Predict the magnetic nature of A and B. 

(a) Both are diamagnetic 

(b) A is diamagnetic and B is paramagnetic with one unpaired electron. 

(c) A is diamagnetic and B is paramagnetic with two unpaired electrons. 

(d) Both are paramagnetic.

Answer 1

The correct option (c) A is diamagnetic and B is paramagnetic with two unpaired electrons. 

Explanation:

In cyano complex K₂[Ni(CN)₄], complex ion is [Ni(CN)₄]^2- and Ni is present as Ni²⁺ or Ni (II), so

In it unpaired electron is not present, so it is diamagnetic in character (square planar shape) 

In chloro complex K₂ [Ni(Cl)₄], complex ion is [N(Cl)₄]^2- and Ni is present as Ni²⁺ or Ni (II), so 

Ni²⁺ = 1s², 2s² 2p⁶, 3s⁶3d⁸,4s⁰

In [Ni(Cl₄)]^2- ion, Ni²⁺ is present as follows due to weaker ligand character of Cl^- ion. (Cl^- is weak field ligand). So it is unable to pair up the electron and Ni²⁺ needs four empty orbitals to accommodate four Cl^- ligand. Thus, (NiCl₄)^2- shows sp³-hybridisation (Tetrahedral shape)

Hence, due to presence of unpaired orbitals, it is paramagnetic in character.