Chapter 23.4, Problem 23.7AFP

Interpretation Introduction

Interpretation:

The number of unpaired electrons and it has a high-spin or low-spin complex ion has to be identified from the given complex ${\left[{\text{Mn(CN)}}_{\text{6}}\right]}^{3-}$.

Concept introduction:

Strong-field ligands and low-spin complexes: In contrast, strong-field ligands, such as ${\text{CN}}^{\text{-}}\text{in}{\left[{\text{Mn(CN)}}_{\text{6}}\right]}^{\text{3-}}$, cause a large splitting energy, so it takes more energy for electrons to jump to the $eg$ set than to pair up in the $t_{2}g$ set.  Thus, for strong-field ligands, $Epairing<\Delta$.  Therefore, the number of unpaired electrons in the complex ion is less than in the free ion.  Strong-field ligands create low-spin complexes, those with fewer unpaired electrons.

The spectrochemical series is,

  $I^{-}<C{l}^{-}<F^{-}<O{H}^{-}<H_{2}O<SC{N}^{-}<en<N{O}_2^{-}<C{N}^{-}<CO$