Chapter 22.3, Problem 1CP

Interpretation Introduction

Interpretation:

The number of unpaired spins in the given compound is to be determined out of the four given options.

Concept Introduction:

Ligands that cause a high degree of splitting among the $d$ orbital energy levels produce strong magnetic fields and low spin complexes. Weak-field ligands, on the other hand, cause small degree of splitting among the $d$ orbital energy levels and result in high spin complexes.

The weak-field ligand makes valence electrons enter into separate $d$ orbitals ($d_{xy},d_{yz}\text{, }{d}_{zx}\text{ and }{d}_{x^2-y^2},d_{z^2}$) but strong-field ligands make them enter into lower-energy $d$ orbitals ($d_{xy},d_{yz}\text{and }{d}_{zx}$).

Spectrochemical series: ${\text{I}}^{-}{\text{< Br}}^{-}{\text{< Cl}}^{-}{\text{< OH}}^{-}{\text{< F}}^{-}{\text{< H}}_2{\text{O < NH}}_3{\text{< en < CN}}^{-}\text{< CO}$

These ligands are arranged in order of increasing value of $\Delta$.

${\text{CN}}^{-}$ and $\text{CO}$ are strong field ligands because they cause large splitting of the d- orbital.

Strong field ligands form low spin complex.

The halide and hydroxide ion are weak field ligands because they cause less splitting of the d-orbital

Weak field ligands form high spin complex.