Question

Which one of the following cyano complexes would exhibit the lowest value of paramagnetic behaviour ?
(Atomic no. Cr = 24, Mn = 25, Fe = 26, Co = 27)

• A. ${\left[Co{\left(CN\right)}_6\right]}^{3-}$
• B. ${\left[Fe{\left(CN\right)}_6\right]}^{3-}$
• C. ${\left[Mn{\left(CN\right)}_6\right]}^{3-}$
• D. ${\left[Cr{\left(CN\right)}_6\right]}^{3-}$

Answer 1

Answer: (A)

$\begin{array}{cccc}& Hybridi-sation& Unpairedelectrons& Magneticmoment\\ \left(a\right){\left[Co{\left(CN\right)}_6\right]}^{3-}& d^{2}s{p}^3& 0& 0\\ \left(b\right){\left[Fe{\left(CN\right)}_6\right]}^{3-}& d^{2}s{p}^3& 1& \sqrt{3}BM\\ \left(c\right){\left[Mn{\left(CN\right)}_6\right]}^{3-}& d^{2}s{p}^3& 2& \sqrt{8}BM\\ \left(d\right){\left[Cr{\left(CN\right)}_6\right]}^{3-}& d^{2}s{p}^3& 3& \sqrt{15}BM\end{array}$
Thus least paramagnetism is in (a).