Interactions of zinc(II), magnesium(II) and calcium(II) with iminodimethylenediphosphonic acids in aqueous solutions†

Abstract

N-Substituted iminodimethylenediphosphonic acids exhibited high complexation efficiency towards zinc(II), magnesium(II) and calcium(II) ions. This results from both dinegatively charged phosphonate groups as well as the imino-nitrogen present in their structure. A significant preference for an equimolar stoichiometry and a formation of tridentate bonded species has been demonstrated in these systems. The only exception is the N-tetrahydrofurylmethyliminodimethylenediphosphonic acid with a tetrahydrofuryl moiety placed in the sterically favoured position that allows its oxygen atom to be an effective metal binding site. Iminodimethylenediphosphonic and N-methyliminodimethylenediphosphonic acids behave quite differently upon zinc(II) complexation forming presumably layered two-dimensional polymeric species. These species disappear upon dilution. The crystal structure of N-methyliminodimethylenediphosphonic acid has also been determined. A unique 3-D arrangement of this compound with a tetramer as a basic building unit has been indicated.