Question

Deduce the shape and magnetic behaviour of the complex ion [Co(NH₃)₅NO₂]²⁺.

Answer 1

1. The complex ion [Co(NH₃)₅NO₂]²⁺ contains cobalt in the +3 oxidation state.
2. Cobalt in the +3 oxidation state has an electron configuration of  3d⁶. 
3. The ligands present ammonia (NH₃) and nitrite \[\ce{(NO^-_2})\] are both considered strong field ligands.
4. The strong field ligands cause the pairing of electrons in the 3d orbitals of the metal ion.
5. Due to this pairing, all six electrons occupy the lower-energy 3d orbitals, and there are no unpaired electrons left.
6. The cobalt ion undergoes d²sp³ hybridisation using two 3d orbitals, one 4s orbital, and three 4p orbitals.
7. The d²sp³ hybridization leads to an octahedral geometry for the complex.

Since there are no unpaired electrons in the complex, it exhibits diamagnetic behaviour (i.e., it is not attracted to a magnetic field). The complex ion [Co(NH₃)₅NO₂]²⁺ has an octahedral shape and is diamagnetic in nature.