ESTIMATING THE STABILITY OF METAL–LIGAND BONDING IN CARBOXYL-CONTAINING POLYMER COMPLEXES BY IR SPECTROSCOPY

The stability of metal–ligand (carboxyl-containing polymer (CCP)) bonding in transition metal complexes is estimated and juxtaposed using Δν(COO) values. The Δν(COO) value is determined from the difference between stretching vibrations of the carboxylate ion in the IR spectra. It is shown that Δν(COO) values for transition metal complexes with ethylenediaminetetraacetic acid (EDTA) increase in the order that directly depends on the order of their stability in the series Fe3+ > Cr3+ > Cu2+ > Ni2+ > Co2+ > Mn2+. The established relationship between the Δν(COO) value and the stability of metal complexes is used to determine the series of metal affinity for carboxyl-containing biopolymers such as citrus pectin (CP) and chitosan succinate (CS). The obtained data indicate that the affinity for metal corresponds to series Cr3+ > Cu2+ > Co2+ > Mn2+ > Ni2+ for citrus pectin (CP) and to series Cu2+ > Cr3+ ≈ Ni2+ ≈ Co2+ > Mn2+ for chitosan succinate (CS).