Chapter 20, Problem 72QRT

(a)

Interpretation Introduction

Interpretation:

Number of unpaired electrons in ${{\text{[Cr(H}}_{\text{2}}{\text{O)}}_{\text{6}}\text{]}}^{\text{2+}}$ has to be given.

Explanation of Solution

Given complex ion is ${{\text{[Cr(H}}_{\text{2}}{\text{O)}}_{\text{6}}\text{]}}^{\text{2+}}$.  The central metal ion is ${\text{Cr}}^{\text{2+}}$.  ${\text{Cr}}^{\text{2+}}$ ion is said to contain four $3d$ electrons.  For high-spin complex, the number of unpaired electrons will be more and for low-spin complex, the number of unpaired electrons will be less.  The splitting of orbitals depends upon the ligand.  If the ligand is weak field ligand, then the crystal field splitting energy (${\Delta }_{\text{o}}$) will be smaller resulting in unpaired electrons.  If the ligand is a strong field ligand, then the crystal field splitting energy will be larger resulting in pairing of electrons.  The crystal field model for high-spin and low-spin complex of ${\text{Cr}}^{\text{2+}}$ can be given as,

Number of unpaired electrons:

The ligand that is present in the complex is water.  Water is a weak field ligand.  Therefore, it forms high spin complex.  From the above drawn crystal field model, it is found that there are four unpaired electrons in high-spin complex.

(b)

Interpretation Introduction

Interpretation:

Number of unpaired electrons in ${{\text{[Mn(H}}_{\text{2}}{\text{O)}}_{\text{6}}\text{]}}^{\text{2+}}$ has to be given.

Explanation of Solution

Given complex ion is ${{\text{[Mn(H}}_{\text{2}}{\text{O)}}_{\text{6}}\text{]}}^{\text{2+}}$.  The central metal ion is ${\text{Mn}}^{\text{2+}}$.  ${\text{Mn}}^{\text{2+}}$ ion is said to contain five $3d$ electrons.  For high-spin complex, the number of unpaired electrons will be more and for low-spin complex, the number of unpaired electrons will be less.  The splitting of orbitals depends upon the ligand.  If the ligand is weak field ligand, then the crystal field splitting energy (${\Delta }_{\text{o}}$) will be smaller resulting in unpaired electrons.  If the ligand is a strong field ligand, then the crystal field splitting energy will be larger resulting in pairing of electrons.  The crystal field model for high-spin and low-spin complex of ${\text{Mn}}^{\text{2+}}$ can be given as,

Number of unpaired electrons:

The ligand that is present in the complex is water.  Water is a weak field ligand.  Therefore, it forms high spin complex.  From the above drawn crystal field model, it is found that there are five unpaired electrons in high-spin complex.

(c)

Interpretation Introduction

Interpretation:

Number of unpaired electrons in ${{\text{[FeF}}_{\text{6}}\text{]}}^{3-}$ has to be given.

Explanation of Solution

Given complex ion is ${{\text{[FeF}}_{\text{6}}\text{]}}^{3-}$.  The central metal ion is ${\text{Fe}}^{\text{3+}}$.  ${\text{Fe}}^{\text{3+}}$ ion is said to contain five $3d$ electrons.  For high-spin complex, the number of unpaired electrons will be more and for low-spin complex, the number of unpaired electrons will be less.  The splitting of orbitals depends upon the ligand.  If the ligand is weak field ligand, then the crystal field splitting energy (${\Delta }_{\text{o}}$) will be smaller resulting in unpaired electrons.  If the ligand is a strong field ligand, then the crystal field splitting energy will be larger resulting in pairing of electrons.  The crystal field model for high-spin and low-spin complex of ${\text{Fe}}^{\text{3+}}$ can be given as,

Number of unpaired electrons:

The ligand that is present in the complex is fluorine.  Fluorine is a weak field ligand.  Therefore, it forms high spin complex.  From the above drawn crystal field model, it is found that there are five unpaired electrons in high-spin complex.

(d)

Interpretation Introduction

Interpretation:

Number of unpaired electrons in ${{\text{[Cr(en)}}_{\text{3}}\text{]}}^{3+}$ has to be given.

Explanation of Solution

Given complex ion is ${{\text{[Cr(en)}}_{\text{3}}\text{]}}^{3+}$.  The central metal ion is ${\text{Cr}}^{\text{3+}}$.  ${\text{Cr}}^{\text{3+}}$ ion is said to contain three $3d$ electrons.  For high-spin complex, the number of unpaired electrons will be more and for low-spin complex, the number of unpaired electrons will be less.  The splitting of orbitals depends upon the ligand.  If the ligand is weak field ligand, then the crystal field splitting energy (${\Delta }_{\text{o}}$) will be smaller resulting in unpaired electrons.  If the ligand is a strong field ligand, then the crystal field splitting energy will be larger resulting in pairing of electrons.  In this ion, there are only three $d$ electrons and the lower-energy orbitals has to be singly filled first.  Therefore, only one configuration is possible and it is shown as given below.

Number of unpaired electrons:

The ligand that is present in the complex is ethylenediamine.  From the above drawn crystal field model, it is found that there are three unpaired electrons in complex.