Chapter 20, Problem 20.121CHP

Interpretation Introduction

Interpretation:

The bonding for given complex ${\left[\text{Mn}{\left(\text{CN}\right)}_{\text{6}}\right]}^{\text{3-}}$ should be described by using both valence bond and crystal field theory. The number of electrons and the model predicts the number of unpaired electrons should be identified.

Concept Introduction:

Valence bond theory: It is used to describe bonding present in molecules.

Based on valence bond theory the bonding in complexes arises as result of orbital overlap between electron filled ligand and vacant hybrid metal orbital which gives a coordinate covalent bond between them.

$Spectrochemical$ Series: The list of ligands arranged in an ascending order of $\text{(Δ)}$(the splitting of d-orbitals in presence of various ligands).

$\begin{array}{l}\stackrel{{}^{{\text{I}}^{\text{-}}\text{<}{\text{Br}}^{\text{-}}\text{<}{\text{SCN}}^{\text{-}}\text{<}{\text{Cl}}^{\text{-}}\text{<}{\text{S}}^{\text{2-}}\text{<}{\text{F}}^{\text{-}}\text{<}{\text{OH}}^{\text{-}}\text{<}{\text{O}}^{\text{2-}}\text{<}{\text{H}}_{\text{2}}\text{O}\text{<}{\text{NCS}}^{\text{-}}\text{<}{\text{edta}}^{\text{4-}}\text{<}{\text{NH}}_{\text{3}}\text{< en}\text{<}{\text{NO}}^{\text{2-}}\text{<}{\text{CN}}^{\text{-}}\text{<}\text{CO}}}{\to }\\ {}_{{}^{{}^{\begin{array}{l}\text{weak-field}\text{increasing(Δ)}\text{strong-field}\\ \text{ligands}\text{ligands}\end{array}}}}\end{array}$

The strong-field ligands results in pairing of electrons present in the complex and leads to diamagnetic species, while the low-field ligand do not have tendency to pair up the electrons therefore forms paramagnetic species.

Crystal Field Theory: It is the next advancement of valence bond theory which helps to understand the bonding in coordination complexes, identify the spin of the complex that is whether it will be a high spin or low spin and to find the color of the complex.