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)

$\begin{matrix}&Hybridi-sation&Unpaired \,electrons&Magnetic \,moment\\ \left(a\right) \left[Co\left(CN\right)_{6}\right]^{3-}&d^{2}sp^{3}&0&0\\ \left(b\right) \left[Fe\left(CN\right)_{6}\right]^{3-}&d^{2}sp^{3}&1&\sqrt{3}\,BM\\ \left(c\right) \left[Mn\left(CN\right)_{6}\right]^{3-}&d^{2}sp^{3}&2&\sqrt{8}\,BM\\ \left(d\right) \left[Cr\left(CN\right)_{6}\right]^{3-}&d^{2}sp^{3}&3&\sqrt{15}\,BM\end{matrix}$
Thus least paramagnetism is in (a).