Question

The complex $\left[Fe\right(H_{2}O{)}_{5}NO{]}^{2+}$ is formed in the brown ring test for nitrates when freshly prepared $FeS{O}_4$ solution is added to aqueous solution of $N{O}_3^{-}$ followed by addition of concentrated $H_{2}S{O}_4$. Select correct statements about this complex:

• A. Color change is due to charge transfer
• B. It has iron in $+1$ oxidation state and nitrosyl as $N{O}^{+}$
• C. It has magnetic moment of $3.87\text{B.M.}$ confirming three unpaired electrons in $Fe$
• D. In complex $Fe$ has $d^{2}s{p}^3$ hybridization
  

Answer 1

Answer: (A), (B), (C)

It has magnetic moment of $3.87\text{B.M.}$ confirming three unpaired electrons in $Fe$

(a) $F{e}^{2+}$ changes to brown colored ring complex and the color change is due to charge transfer
(b) $NO\to N{O}^{+}+e^{-}F{e}^{2+}+e^{-}\to F{e}^{+}$

$\text{Magnetic moment}=\sqrt{n(n+2)}=\sqrt{15}=3.87\text{BM}$
(d) It is a high sin complex, it contains $3$ unpaired electrons hence, hybridisation of the complex is $s{p}^3{d}^2$.