What is spectrochemical series? Weak field ligand and strong field ligand

What is spectrochemical series?

The main concepts of spectrochemical series is, arrangements of ligands in order of their increasing field strength. we can arrange different ligands, according to increasing field strength. You can understand properly with next paragraph.

The arrangements of ligand in ascending order of crystal field splitting energy (CFSE). and the order remains practically constant for different metals.

According to this terms, you can say that the arrangements of ligands in order of their increasing crystal field splitting energy value, is called spectrochemical series.

Types of ligands;

1. Weak field ligands

The ligands with a small value of crystal field splitting energy (CFSE) , high spin and π doner, are called weak field ligands.

for example

ligands – ∆ < P (p – pairing energy)

2. Stronge field ligands

The Ligands with a large value of crystal field splitting energy, low spin, and π acceptors, are called strong field splitting energy (CFSE). such as,

ligands – ∆ > P ( pairing energy)

Spectrochemical series are stabilised in 1938. It work on the basis of electronic spectroscopy of octahedral CO(II) coordination compounds.

the role of π doner or π acceptors in ligand of spectrochemical series is very important for d-orbitals. and these effect have unique impact on d-orbitals.

Which order is correct in spectrochemical series of ligand?

Conceptually Answer

First of all, i want to say that, spectrochemical series is depends upon increasing crystal field splitting energy. and this term, increasing crystal filed splitting energy is know as spectrochemical series.

second, basic concepts of spectrochemical series is, the main arrangements of ligand in order of their increasing field strengths. this value is know as spectrochemical series.

Order in spectrochemical series of ligand :

In this case, if the value of increasing crystal field splitting energy is small, this is called weak field ligand. Such as, ∆ < P and if the value of increasing crystal field splitting energy is large, this is called strong field ligand. Such as ∆ > P.

Concepts of crystal field splitting energy

When ligands approach with transition metal ion, when we are talking about d-orbitals, there are two different types of sets are persent. One with lower energy and the another with higher energy. this difference of energy between the two different sets of orbitals is called crystal field splitting energy.

For examples,

1. Octahedral field – ∆ {O}
2. Tetrahedral field – ∆ {T}

Draw figure to show the splitting of d-orbitals in an octahedral crystal field.

Splitting of d-orbitals in an octahedral crystal field

Strong field ligands examples

Strong field ligands – loan pair donor atom either nitrogen or carbon then this is called strong field ligands.

Lets know with examples,

Here, there are many loan pair donor atom in which nitrogen Or carbon are donate.

In this example, nitrogen are donate. now i m going to explain with particular atoms in which only nitrogen are donate. these type of atoms donate nitrogen. such as,

Only nitrogen donor

Phen

dipy

In this structure you can see that there are two donor atoms are persent. and donor atoms is nitrogen.

en

Py

CN –

CO

1. en
2. Py

Importance of spectrochemical series