question_answer

Which one of the following is an inner orbital complex as well as diamagnetic in behaviour? [AIPMT (S) 2005]

(Atomic no. : 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) \[{{[Ni\,{{(N{{H}_{3}})}_{6}}]}^{2+}}\]

Correct Answer: B

Solution :

[b] In [Co(NH3)6]3+, oxidation state of Co = + 3 and its co-ordination number is six.

So              \[_{27}Co=1{{s}^{2}},2{{s}^{2}},2{{p}^{6}},3{{s}^{2}}3{{p}^{6}},3{{d}^{7}},4{{s}^{2}}\]

\[C{{o}^{3+}}=1{{s}^{2}},2{{s}^{2}}2{{p}^{6}},3{{s}^{2}}3{{p}^{6}}3{{d}^{6}}\]

In [Co(NH3)6]3+ shows inner orbital complex as well as diamagnetic in behaviour (due to absence of upaired electron).

[Zn(NH3)6]3+ \[\to \] sp3d2  hybridisation   (outer) and diamagnetic.

\[{{[Cr{{(N{{H}_{3}})}_{6}}]}^{2+}}\to \,{{d}^{2}}s{{p}^{3}}\] hybridisation   (inner) and paramagnetic.