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Q.
Which one of the following is an inner orbital complex as well as diamagnetic in behaviour? (At. no. of $Zn = 30, Cr = 24, Co = 27, Ni = 28$)
AIPMTAIPMT 2005Coordination Compounds
Solution:
In $\left[ Co \left( NH _{3}\right)_{6}\right]^{3+}$, oxidation state of $Co =+3$ and its coordination number is six.
${ }_{27} Co =1 s^{2}, 2 s^{2} 2 p^{6}, 3 s^{2} 3 p^{6} 3 d^{7}, 4 s^{2} $
$ Co ^{3+}=1 s^{2}, 2 s^{2} 2 p^{6}, 3 s^{2} 3 p^{6} 3 d^{6}$
$\left[ Co \left( NH _{3}\right)_{6}\right]^{3+}$ is an inner otbital complex as well as diamagnetic in behaviour (due to absence of unpaired electrons).
$\left[ Zn \left( NH _{3}\right)_{6}\right]^{2+} \rightarrow s p^{3} d^{2}$ hybridisation (outer orbital and diamagnetic).
$\left[ Cr \left( NH _{3}\right)_{6}\right]^{3+} \rightarrow d^{2} Sp ^{3}$ hybridisation (inner orbital and paramagnetic).
