COMPLEXATION PROPERTIES OF 2,6-PYRIDINE-B IS(METHYLAMINE)-N,N,N',N'-TETRAACETIC ACID

The complexation properties of ,6-pyridine-bis(methylamine)-N,N,N',N'- tetraacetic acid (H4PBMTA) were studied. The protonation constants and the stability constants of the Ca2+, Sr2+, Zn2+, Cd2+, Pb2+, La3+, Nd 3+, Gd3+, Ho3+ and Lu3+ complexes were determined by pH-potentiometry. , The stability constants (log K) are 3-4 orders of magnitude lower th an those of the DTPA complexes but the trend in the logK values of the lanthanide complexes of PBMTA and DTPA is similar. The H-1-NMR signal of the acetate methylene protons of the LnPBMTA complexes is an AB qu artet, indicating the long life-time of the Ln3+-N bond. The exchange reaction between the CePBMTA- and Y3+ ions takes place by the spontane ous and proton assisted dissociation of the complex. The proton assist ed dissociation is slower for the CePBMTA- than for the CeDTPA2- indic ating the higher importance of the rigid structure of PBMTA in the kin etic stability than in the thermodynamic stability of its complexes.