Question

Rank the following ligands in order of increasing Kf with Co2+:

H₂O

NO₂^-

TEA (Triethanolamine)

En (Ethylenediamine)

EDTA (Ethylenediaminetetraacetic acid)

Answer 1

K_f is the formation constant and it measures the strength of the reaction between metal and ligand during formation of the complex. Co²⁺ is the metal cation and it readily reacts with NO2^- anion to form the product compound.Ethylenediamine (En) is a bidentate chelating agent so it has two donor sites (each N atom for each amine group). Donor sites in EDTA are two N atoms of the amine group and 4 negatively charged oxygen atoms and TEA has one N atom as the donor site. H₂O is not a strong ligand for complex formation.

For this reason, the order of increasing Kf is as follows:

H₂O < TEA < EDTA < En < NO₂^-