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Charakterystyka równowag kompleksowania kwasów iminodi(metylenofosfonowych) z jonami metali(II)

Kamecka A., Kurzak B.

Wiadomości Chemiczne

2002

[Z] 56, 3-4

315-339

The aminopolyphosphonic acids are analogues of aminopolycarboxylic acids in which the carboxyl groups (CO2-) are substituted by the phosphonate moieties (PO32-). Aminopolyphosphonic acids and their derivatives have received considerable attention because of their interesting biological activity and a wide range of uses for industrial, chemical, agricultural and pharmacological purposes. This review discusses coordination preferences of N-substituted iminodi(methylenephosphonic) acids to the divalent metal ions (such as magnesium, calcium, manganese, cobalt, nickel, copper and zinc) in an aqueous solution. N-substituted derivatives of iminodi(methylenephosphonic) acids exhibit high complexation efficiency towards divalent metal 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 has been demonstrated in these systems. The only exeption is the N-2-methyltetrahydrofuryliminodi(methylenephosphonic) acid with a tetrahydrofuryl moiety placed in the sterically favoured position that allows its oxygen atom to be an effective metal binding site. Specific interactions between metal ions and furyl oxygen results in higher binding ability of this ligand and a formation of 1:2 species. The first part of the review deals with the acid-base properties of the considered ligands which are consistent with electronic effect of the substituents attached to the imino nitrogen. The second part of the review describes the binding properties of iminodi(methylenephosphonic) acids in copper(II) complexes. A formation of tridentate bonded species has been demonstrated in these systems. The third part of the review report what is known about magnesium(II), calcium(II) and zinc(II) complexes of the same ligands. While the imino nitrogen is bonded in the predominate complexes in the zinc(II) systems, magnesium(II) and calcium(II) ions prefer a pure phosphonate coordination. Finally, the interactions of manganese(II), cobalt(II) and nickel(II) ions with N-substituted iminodi(methylenephosphonic) acids are described. For these complexes the formation of eight-membered rings is reported. Coordination properties of iminodi(methylenephosphonic) acids are important factors to understand the role of the ligands and metal ions in biological systems.