Hello, reders welcome to “chemwhite.com” today i am going to explain about the term spectrochemical series.
What is spectrochemical series?
Actually, the main function of spectrochemical series, they developed the arrangement of ligands in the increases order of crystal field splitting. It is arrangements of ligands from weak ligands and strong ligands. this is known as spectrochemical series.
but crystals field splitting is greater if ligands are stronger and they form complex with the help of high spin.
The spectrochemical series is a tool used to rank ligands based on their ability to split the d-orbitals of a transition metal ion in a complex.
This splitting, known as ligand field splitting, arises from the electrostatic interaction between the metal d-orbitals and the ligand’s electrons.
Ligands that cause a large splitting are called strong-field ligands, while those that cause a small splitting are referred to as weak-field ligands.
Adsorption of light by coordination compound with different ligands are know as spectrochemical series.
Read More – What are inner-transition elements?
Difference between weak field ligands and strong field ligands
- Weak filed ligands
- Stronge field ligands
Weak field ligands – It mean, less splitting of crystal field. and thy form complex with the help of high spin.
The arrangements of ligands on the basis of electrons pair (loan pair) doner ability. this mean, ligands have ability to break down of reservancy for central metals ion of d orbitals. this type of legands is known as stronge ligands.
Doner atom is oxygen and sulfur and helogen.
(d) Br-, SCN-, O-2, NO3- and more
Chlorine ions and fluoride ion
stronge field ligands – It mean, greater splitting of crystal field. and they form complex with the help of low spin.
The arrangements of ligands on the basis of electrons pair (loan pair) doner ability. this mean, ligands have not ability to break down of reservancy for central metals ion of d orbitals. this type of legands is known as weak ligands.
Carbon doner ligands and nitrogen doner ligands are the best example of strong ligands.
(f) CO and cyanide ion.
Importance of spectrochemical series?
- The arrangements of ligands on the basis of electrons pair (loan pair) doner ability.
- loan pair doner either carbon or nitrogen.
- strong ligands means, having ability of loan pair doner atom. for examples, carbon and nitrogen.
- ligands have ability to break down of reservancy of central metals ion of d orbitals. this type of legands is known as stronge ligands.
- weak ligands means, doner atom should be oxygen, and sulfur.
- weak ligands having ability doner atom such as oxygen, sulfur and helogen.
- ligands have not ability to break down of reservancy for central metals ion of d orbitals. this type of legands is known as weak ligands.
- In case of weak ligands, doner atom such as, oxygen (O) sulphur (S) and helogen (F, Cl, Br, l).
- The best examples of weak ligands are,
- Weak ligands are, H2O, OH-, Cl- , Br- , NO3- , O-, SCN-, NO3-
- The best example of strong ligands are,
- Strong ligands are, CN-, NO2-, dipy, eN, NH3.
Electrochemical series / Reactivity series
- K (potassium) Pb (Lead)
- Na (sodium) H (hydrogen)
- Ca (calsium) Cu (copper)
- Mg (magnesium) Ag (silver)
- Al (Aluminium) Au (gold)
- Zn (Zinc) pt (platinum)
- Fe (iron)
- Sn (Tin)
Short tric of spectrochemical series
It is define as the series obtained when ligands are arange according to CFSE (crystal field stable energy). the series obtained is called spectrochemical series.
The starting ligands of spectrochemical series are I, Br (halogen) these are weak ligands.
In between of spectrochemical series are H2O.
Strongest ligands are CN-, CO.
Arrangements of weak field ligands
I- < Br- < Cl- < SCN- < F- < OH- < CH3COO- < C2O4 < H2O.
Arrangment of strong field ligands
HCN < NH3 < Py < en < diph < NO2 < H- < CO-
Arrangment of ligands in order their field strength.
The Spectrochemical Series Order
The spectrochemical series arranges ligands in order of increasing strength or ability to induce ligand field splitting. The series typically follows the order:
Weak-field ligands: I- < Br- < S2- < SCN- < Cl- < F- < OH- < C2O42- < H2O < NCS- < pyridine < NH3 < en < NO2- < phen < CN-.
Strong-field ligands: CO < CN- < NO+ < phenanthroline < bipyridine < oxalate < EDTA4-.
Aplication of spectrochemical series
Color and Absorption Spectra
The spectrochemical series helps explain the colors observed in transition metal complexes.
Strong-field ligands cause large energy separations between the d orbitals, resulting in absorption of higher energy (visible) light and thus appearing complementary in color.
Weak-field ligands lead to small energy separations, absorbing lower energy (UV) light, which is not visible to the human eye.
Stability and Reactivity
The position of a ligand in the spectrochemical series affects the stability and reactivity of the resulting complex.
Strong-field ligands form more stable complexes due to increased ligand field splitting, leading to greater kinetic and thermodynamic stability.
On the other hand, weak-field ligands result in less stable complexes, making them more susceptible to substitution reactions.
The spectrochemical series guides the understanding of ligand substitution reactions. According to the Irving-Williams series, as we move down the periodic table, the preference for strong-field ligands increases, while weak-field ligands are preferred for smaller transition metals. This knowledge is vital for designing catalysts and understanding the reactivity of coordination compounds.
The spectrochemical series finds applications in bioinorganic chemistry, particularly in the study of metalloenzymes and their reactivity.
It helps elucidate the binding preferences of metal ions in the active sites of enzymes, offering insights into their functions and catalytic mechanisms.