Question

Predict the order of $\Delta_{o}$ for the following compounds:
$I. \left[Fe\left(H_{2}O\right)_{6}\right]^{2+} \quad II. \left[Fe\left(CN\right)_{2}\left(H_{2}O\right)_{4}\right]$
$III. \left[Fe\left(CN\right)_{4}\left(H_{2}O\right)_{2}\right]^{2-}$

• A. $\Delta_{o}\left(I\right) < \Delta _{o}\left(II\right) < \Delta _{o}\left(III\right)$
• B. $\Delta_{o}\left(II\right) < \Delta _{o}\left(I\right) < \Delta _{o}\left(III\right)$
• C. $\Delta_{o}\left(III\right) < \Delta _{o}\left(II\right) < \Delta _{o}\left(I\right)$
• D. $\Delta_{o}\left(II\right) < \Delta _{o}\left(III\right) < \Delta _{o}\left(I\right)$

Answer 1

Answer: (A)

The value of $\Delta_{o}$ for mixed ligands depends on the additive contributions of the ligand strengths. Since $CN^-$ has greater ligand strength than $H_2O$, the strength increases as the number of $CN^-$ ions increases.