COMPLEXATION OF LANTHANIDE IONS BY DIETHYLENETRIAMINE-N,N',N''-PENTA-BETA-PROPIONATE

The stability constants for the formation of the lanthanide chelates L nH2DTPP0 and LnH3DTPP+ diethylenetriamine-N,N',N''-penta-beta-propiona te) have been measured in solutions of 0.50 M (NaClO4) ionic strength by pH measurement. The similar stabilities of the two complexes indica te that both species involve similar binding sites of the ligand. The similarity in their entropy and enthalpy values also support such a mo del. Fluorescence data indicate that the primary coordination sphere o f the Eu(III) ion in both complexes contains 5.5 +/- 0.5 water molecul es compared to the value of 8.8 +/- 0.5 for the free Eu(III)(aq) ion. This is consistent with binding of the lanthanide ion via three donor sites of DTPP.