[Cr(NH3)6]3+ is paramagnetic while [Ni(CN)4]2– is diamagnetic. Explain why?
Overall charge balance in [Cr(NH3)6]3+ complex:
X + 6(0) = + 3
X = + 3
Cr is in + 3 oxidation state.
Electronic configuration of Cr in + 2 state: 3d3 . Now ammonia is a weak field ligand so it not causes pairing of the unpaired electron and undergoes hybridisation to form 6 sp3d2 hybrid orbitals filled by the six ammonia ligands. It's geometry is octahedral with unpaired electrons and hence is paramagnetic complex.
In case of [Ni(CN)4]2– ion :
Overall charge balance in [Ni(CN)4]2–complex:
X + 4(-1) = -2
X = + 2
Ni is in + 2 oxidation state.
Electronic configuration of Ni in + 2 state: 3d8. Now cyanide ion is a strong field ligand so it causes pairing of the unpaired electron and undergoes hybridisation to form 4 dsp2 hybrid orbitals filled by the four cyanide ligands. It's geometry is square planar with no unpaired electrons and hence is diamagnetic complex.
