A spectral study of transition-metal complexes on a chelating ion-exchange resin containing aminophosphonic acid groups

The coordination mode of a commercial chelating ion-exchange resin, ES 467, containing aminomethylphosphonic acid groups anchored on a macroporous styrenedivinylbenzene copolymer, with several metal ions, such as chromium(III), cobalt(II), nickel(II), copper(II) and zinc(II) has been studied with the aid of IR, ligand field and ESR spectra. The chelating group of ES 467, aminomethylphosphonic acid, appears to bind different metal ions mainly through oxygen atoms of the phosphonic acid group, though, in the case of those species containing low-loading of metal ions, the secondary amine nitrogen atom also appears to take part in coordination. Most of the metal ions studied seem to be present as six-coordinated species in the polymeric matrix, whereas cobalt(II) species show electronic spectra which are consistent with the presence of both four-coordinated (tetrahedral) and six-coordinated (octahedral) structures of these species. The distribution coefficients for cobalt(II), nickel(II), copper(II) and zinc(II) have been determined and it appears that the resin ES 467 binds copper(II) ions selectively. An attempt has been made to find a possible relationship between the selectivity of the chelating resin and the stereochemistry of the adsorbed metal ions.