Question

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

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

Answer 1

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

(1) $\left[Ti\right(N{H}_3{)}_6{]}^{3+}:3d^1$ Configuration and thus has one unpaired electron.
(2) $\left[Cr\right(N{H}_3{)}_6{]}^{3+}$ : The complex is inner orbital complex but $3d^3$ configuration has three unpaired electrons with weak as well as with strong field ligand.
(3) $\left[Co\right(N{H}_3{)}_6{]}^{3+}$ : The cobalt ion in +3 oxidation state with $3d^6$ configuration represented as shown below.

It has no unpaired electron.

(4) $\left[Zn\right(N{H}_3{)}_6{]}^{3+}$ : Because of $3d^{10}$ configuration no (n-1)d orbital is available for $d^{2}s{p}^3$ hybridisation and thus forms outer orbital complex. The complex is diamagnetic.

Thus, complex in option (b) has more unpaired electron so it has highest magnetic moment.