Retraction of "Synthesis and Solution Studies of the Complexes of Trivalent Lanthanides with the Tetraazamacrocycle TETA-(PO)2".

Abstract

A new potentially multidentate hexaprotic ligand H6[TETA-(PO)2] has been prepared by reaction of ethylenediamine-N,N‘-diacetic acid (EDDA), paraformaldehyde, and phosphinic acid; its coordination properties with three lanthanide ions (La3+, Gd3+, and Lu3+) have been explored. The structures of the complexes were studied in aqueous solution by potentiometric pH titrations and by 31P NMR spectroscopy. Four acidity constants were determined potentiometrically in the range 2.5 < pH < 14. The four measured pKa values can be divided into two groups, and within each group the initial deprotonation was found to have little effect on the second. Variable temperature 31P and 31P{1H} EXSY NMR spectra showed that, for [Lu(TETA-(PO)2)]3-, the two phosphorus atoms exist in different chemical environments and undergo an exchange process which is very fast on the NMR time scale at room temperature. This result is consistent with one of the phosphinate residues coordinating the metal ion and exchanging with a free analogu...