SYNTHESIS AND DYNAMIC PROPERTIES OF KINETICALLY INERT LANTHANIDE COMPOUNDS - LANTHANUM(III) AND EUROPIUM(III) COMPLEXES OF 1,4,7,10-TETRAKIS(2-HYDROXYETHYL)-1,4,7,10-TETRAAZACYCLODODECANE

The synthesis and dynamic properties of La(THED)(CF3SO3)3 and Eu(THED)(CF3SO3)3 are described. (THED is 1,4,7,10-tetrakis(2-hydroxyethyl)-1,4,7,10-tetraazacyclododecane.) Variable-temperature H-1 and C-13 NMR studies indicate that the ethylenic groups of the 12-membered tetraaza macrocycle are rigid on the NMR time scale at low temperatures (-40-degrees-C), and all adopt the same conformation. Macrocycle rigidity is lost at elevated temperatures. A dynamic process involving conformational changes of the ethylenic groups in the tetraazamacrocycle is consistent with NMR data. An energy barrier of 52 (4-0.7) kJ mol-I is calculated for this process from line-shape analysis of C-13 NMR spectra of La(THED)(CF3SO3)3 at four temperatures. Both complexes arc stable in water at near-neutral pH. The dissociation of La3+ or Eu3+ from their respective complexes is investigated in the presence of excess Cu2+ by monitoring an absorbance at 312 nm attributed to the Cu(THED)2+ complex. For La(THED)(CF3SO3)3, dissociation is first-order in lanthanum complex and independent of CU2+ with a first-order rate constant of 9.2 (+/-0.5) X 10(-6) s-1 at 37-degrees-C, pH 6.0. Eu(THED)(CF3SO3)3 is substantially more inert to metal ion release than is the lanthanum complex. The first-order rate constant for dissociation of the europium complex at pH 6.0 and 37-degrees-C is 7.1 (+/-0.4) X 10(-7) s-1; there is a slight dependence of the rate constant on pH in the pH range 3.0-6.8.