Question

Which of the following complex compounds will exhibit highest paramagnetic behaviour? $(At.No.Ti=22,Cr=24,Co=27,Zn=30)$

• A. $\left[Zn\right(N{H}_3{)}_6{]}^{2+}$
• B. $\left[Ti\right(N{H}_3{)}_6{]}^{3+}$
• C. $\left[Cr\right(N{H}_3{)}_6{]}^{3+}$
• D. $\left[Co\right(N{H}_3{)}_6{]}^{3+}$

Answer 1

The correct option is C $\left[Cr\right(N{H}_3{)}_6{]}^{3+}$

Paramagnetism is decided by no of unpaired electrons in various subshells of the atoms in a molecule of the compound. Since ligand i.e. NH₃ is same for all 4 options and on observing the central atom and charge it is clear that no of unpaired electron is no of unpaired electrons in 3d orbitals of these atom. Now Zn²⁺,Ti³⁺,Cr³⁺,Co³⁺ has 10,1,3,6 e^- in their 3d orbitals respectively. Since NH₃ is strong field ligand therefore it will pair the e^- in t_2g orbitals and hence will have 0,1,3,0 unpaired electrons. Therefore option(C) is most paramagnetic.