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

N-Substituted iminodimethylenediphosphonic acids exhibited high complexatio n efficiency towards zinc(II), magnesium(II) and calcium(II) ions. This res ults from both dinegatively charged phosphonate groups as well as the imino -nitrogen present in their structure. A significant preference for an equim olar stoichiometry and a formation of tridentate bonded species has been de monstrated in these systems. The only exception is the N-tetrahydrofurylmet hyliminodimethylenediphosphonic acid with a tetrahydrofuryl moiety placed i n the sterically favoured position that allows its oxygen atom to be an eff ective metal binding site. Iminodimethylenediphosphonic and N-methyliminodi methylenediphosphonic acids behave quite differently upon zinc(II) complexa tion forming presumably layered two-dimensional polymeric species. These sp ecies disappear upon dilution. The crystal structure of N-methyliminodimeth ylenediphosphonic acid has also been determined. A unique 3-D arrangement o f this compound with a tetramer as a basic building unit has been indicated .