Studies on the Infrared Spectra of Some Divalent Transitional Metal Humates

The infrared spectra of humic acid and its complexes with Cu (II), Fe (II), Zn (II), Mn (II) and Co (II) hove been studied. It is observed that the hydroxyl stretching vibration is perturbed by its coordination to a metal ion. The maximum frequency shift from 3413 cm^−l in acid to 3325 cm^−l in iron (II) humate is observed. The frequency of coordinated hydroxyl group is found to vary in the order: Mn > Co > Cu > Fe < Zn. The ionised carboxyl group stretching frequency is very little affected by the metal ion, which indicates a purely ionic (or partial covalent) bonding.