Question

Which one of the following is an inner orbital complex as well as diamagnetic in behaviour? (Atomic number of $Zn=30,Cr=24,Co=27,Ni=28$)

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

Answer 1

Answer: (C)

In ${\left[Co{\left(N{H}_3\right)}_6\right]}^{3+}$,
oxidation state of $Co=+3$
and its coordination number is six.
So, ${}_{27}Co=1s^2,2s^2,2p^6,3s^{2}3p^{6}3d^7,4s^2$
$C{o}^{3+}=1s^{2}2s^{2}2p^6,3s^{2}3p^{6}3d^6$

Thus, ${\left[Co{\left(N{H}_3\right)}_6\right]}^{3+}$ shows inner orbital complex as well as diamagnetic in behaviour (due to absence of unpaired electron).
${\left[Zn{\left(N{H}_3\right)}_6\right]}^{2+}\to s{p}^3{d}^2$ hybridisation (outer) and diamagnetic.
${\left[Cr{\left(N{H}_3\right)}_6\right]}^{3+}\to d^{2}s{p}^3$ hybridisation (inner) and paramagnetic.