Chapter 9, Problem 9D.28E

(a)

Interpretation Introduction

Interpretation:

The ligands have to be classified as pi-acid or pi-base on the basis of the definition.

Concept Introduction:

Pi-acid or Pi- acceptor:

Ligands having empty orbitals, which can interact with metal d-orbitals for the formation of $\text{π}$ -bond are called $\text{π}$-acceptor ligands.  This ligand possesses vacant $\text{π*}$-anti-bonding molecular orbitals or empty d- orbitals of metals along with filled $\text{σ}$-orbitals.  On bonding metal d-orbital donate its electron density to empty $\text{π}$-orbital of these ligands and this type of bonding is called $\text{π}$-backbonding.

Pi-base or Pi-donor:

In coordination chemistry a pi-donor ligand is a kind of ligand that is capable with filled non-bonding orbital that overlap with metal-base orbitals.  If the ligand molecule has pi electrons in d-orbitals they are referred as pi-donor.

Example: F anion will donate this density to the metal atom.

(b)

Interpretation Introduction

Interpretation:

The ligands have to be arranged in the order of increasing splitting energy.

Concept Introduction:

Spectrochemical series:

Spectrochemical series is a list of ligands in the order of ligand strength and a list of metal ion based on oxidation number.  In crystal field theory, ligands modify the difference in energy between the d orbitals $\left(\text{Δ}\right)$ called the ligand field splitting parameter for ligands, which is mainly reflected in differences in color of similar metal ligand complexes.

Series of ligands from weak field to strong field is,

  $\begin{array}{l}{\text{I}}^{\text{-}}{\text{<Br}}^{\text{-}}{\text{<S}}^{\text{2-}}{\text{<SCN}}^{\text{-}}{\text{<Cl}}^{\text{-}}{\text{<N}}_{\text{3}}{}^{\text{-}}{\text{<F}}^{\text{-}}{\text{<NCO}}^{\text{-}}{\text{<OH}}^{\text{-}}{\text{<C}}_{\text{2}}{\text{O}}_{\text{4}}{}^{\text{-}}{\text{<O}}^{\text{2-}}\\ {\text{<H}}_{\text{2}}{\text{O<NCS}}^{\text{-}}{\text{<CH}}_{\text{3}}{\text{CN<gly<py<NH}}_{\text{3}}{\text{<bipy<NO}}_{\text{2}}{}^{\text{-}}{\text{<PPH}}_{\text{3}}{\text{<CN}}^{\text{-}}\text{<CO}\end{array}$