Spectroscopic Characterization of a Series of Europium(III) Amino Phosphonate Complexes in Solution
The Eu3+ complexes of nitrilotris (methylenephosphonic acid) (ntp), ethylenediaminetetrakis (methylenephosphonic acid) (edtp), hexamethylenediaminetetrakis (methylenephosphonic acid) (hdtp), and diethylenetriaminepentakis (methylenephosphonic acid) (dtpp) have been characterized in solution by laser-induced Eu3+ luminescence spectroscopy. The latter three ligands form both 2:1 and 1:1 metal-ligand complexes, while ntp forms both 1:1 and 1:2 complexes at pH 6.0. The number of water molecules directly coordinating the metal ion was determined for each complex. The 7F0 -> 5D0 excitation spectra of edtp, hdtp, and dtpp reveal isomeric forms for both the 2:1 and 1:1 complexes while ntp exhibits only single species for both the 1:1 and 1:2 complexes. Marked changes were observed in the Eu3+ 7F0 -> 5D0 excitation spectra of the various species as a function of pH. The temperature dependence of the xcited state lifetime of the Eu3+-edtp system has an activation energy of 5150 cm-1, corresponding to a ligand level this far above the 5D0 state, which is involved in the deexcitation process.