Question

The correct order of the spin only magnetic moment of metal ions in the following low spin complexes,

[V(CN)₆]⁴⁻ , [Fe(CN)₆]⁴⁻ , [Ru (NH₃)₆]³⁺, and [Cr(NH₃)₆]²⁺ , is:
(A) Cr²⁺ > Ru³⁺ > Fe²⁺ > V²⁺ (B) V²⁺ > Cr²⁺ > Ru³⁺ > Fe²⁺
(C) Cr²⁺ > V²⁺ > Ru³⁺ > Fe²⁺ (D) V²⁺ > Ru³⁺ > Cr²⁺ > Fe²⁺

Answer 1

The correct order of the spin only magnetic moment of metal ions in the following low spin complexes is the one in option B ( V²⁺ > Cr²⁺ > Ru³⁺ > Fe²⁺ ).

• Low spin complexes are the one in which pairin of electrons takes place in the lower t2g levels before electrons are filled in the higher eg levels of the d-orbitals.
• The magnetic moment of an ion increases with an increase in the number of unpaired electrons in the metal ion.
• The number of unpaired electrons in the low spin complexes of  V²⁺,Cr²⁺,Ru³⁺ and Fe²⁺ is equal to 3,2,1 and 0 respectively.
• Hence, the order of the  magnetic moment follows from the above numbers of the unpaired electrons in the metal ions.