Classification of Ligands into Weak and Strong Ligands (NEET Chemistry)

Classify weak and strong ligands out of:

(a) OH⁻

(b) F⁻

(c) I⁻

(d) NH₃

(e) CH₃COO⁻

(f) en

(g) CN⁻

(h) Cl⁻

(i) H₂O

F⁻,I⁻,Cl⁻ and H₂O are weak ligands, other are strong ligands.

If true enter 1, else enter 0.

Hint: To answer this question, it’s important to remember the concept of the Spectrochemical series. Strong ligands are able to donate their electron pairs to the acceptor more effectively.

Complete step by step answer:

– The spectrochemical series is essentially a ranking of ligands based on their strength (ability to donate electron pairs) and also lists metal ions according to their oxidation states, group, and identity.

– In crystal field theory, ligands influence the energy gap between d orbitals, known as the ligand-field splitting parameter or crystal-field splitting parameter, which is often reflected in the color variations of similar metal-ligand complexes.

Weak ligands: 

I⁻,Br⁻,SCN⁻,N3⁻,F⁻,H₂NCONH₂,ox²⁻,O²⁻,H₂O,NCS⁻,py,NH₃,en, bpy

Strong ligands: 

NO₂⁻,CH₃⁻,C₆H₅⁻,CN⁻,CO

• Let’s explore the fundamental idea behind crystal field theory.  

Simply put, this theory explains how orbital degeneracy is broken in transition metal complexes due to the presence of ligands. It also describes the strength of metal-ligand bonds, as the stability of the system changes depending on the strength of these bonds.  

Now, let’s examine the distinction between weak ligands and strong ligands.

F⁻,I⁻,Cl⁻,H₂O are weak ligands, others are strong ligands. This statement is false as en is also a weak ligand. en stands for ethylene diamine ligand. Therefore, enter 0.

Note: You should know that sometimes there are exceptional cases where weak field ligand acts as strong field ligand. For example; [PtCl₄]²⁻ and CoF₆³⁻.