Question

Which of the following is an outer orbital complex and exhibits paramagnetic behaviour?

• A. $[Co{F}_6{]}^{3-}$
• B. $\left[Ni\right(N{H}_3{)}_6{]}^{2+}$
• C. $\left[Zn\right(N{H}_3{)}_6{]}^{2+}$
• D. (a) and (b) above.

Answer 1

The correct option is D (a) and (b) above.

Outer orbital complexes are coordination compounds composed of a central metal atom having hybridization of the atomic orbitals including s, p and d orbitals from the outermost shell.
$\left[Ni\right(N{H}_3{)}_6{]}^{2+}$
$N{i}^{2+}=\left[Ar\right]3d^{8}4s^0$
It is outer orbital complex and paramagnetic.
Similarly, $\left[Zn\right(N{H}_3{)}_6{]}^{2+}$ : $s{p}^3{d}^2$ (outer orbital complex), octahedral, diamagnetic.


In complex $[Co{F}_6{]}^{3-}$
Oxidation number of $Co=+3$
Electronic configuration of
$C{o}^{3+}=1s^2,2s^{2}2p^6,3s^{2}3p^6,3d^6$

In $C{o}^{3+}$ number of unpaired electrons is four, and $F^{-}$ is the ligand of week field. Hence, it does not paired up electrons of d-orbital. So, $\left[\right(Co{F}_6){]}^{3-}$ is paramagenetic. it is $s{p}^{3}d$ hybridisation. Thus it is outer orbital complex.