Complexation of trivalent lanthanide cations with amino(O-alkyl)methylenephosphonic acids as the closest organophosphorus analogues of nitrilotriacetic acid

The complexation of new complexones, analogues of nitrilotriacetic ( H 3 NTA ) and nitrilotrimethylenephosphonic ( H 6 NTP ) acids containing monobasic ( O -alkyl)methylenephosphonic fragments as donor groups, with trivalent cations of lanthanides was studied. The stability and deprotonation constants of 1:1 complexes and the fractional distribution of complex forms were determined using pH-metric titration in combination with mathematical modeling. The complexation properties of N -[( O -butyl)hydroxyphosphorylmethyl]iminodiacetic acid were compared with those of H 3 NTA based on the linear free-energy relationships.