Attention Clever Ones : Strong and Weak field Ligands?

Question

What are strong and weak field ligands...how are they classified... How are they different from each other? Please help..i need simple clear explanations..

Answer 1

Ligand field theory is one method for the description of bonding of ligands in transition metal ion coordination complexes.

Strong field ligands tend to be π-acceptors, like Nitrite (NO2−), Triphenylphosphine (PPh3), Cyanide (CN−) and Carbon monoxide (CO).

Weak field ligands tend to be π-donors, like Iodide (I−), Bromide (Br−), Sulfide (S2−) and Thiocyanate (SCN−).