Macrocyclic ligands, lanthanide complexes spectra

Several of the complexes in Figure 2 were examined further for their resistance to dissociation. The europium complexes Eu(THED)3+ and Eu(TCMC)3+ were more difficult to study quantitatively by H NMR because of their broad H resonances. Decomposition was monitored by use of a UV-vis assay. Excess Cu2+ was added to solutions containing the lanthanide macrocycles. The Cu2+ ion served the dual purpose of trapping the free macrocycle and as an indicator to monitor the amount of macrocycle that had dissociated. All Cu(II) macrocyclic complexes gave an absorbance peak in the UV-vis spectrum that was characteristic of the Cu(II) macrocycle complex. For all macrocycles, Cu2+ was an effective trap formation of the Cu(II) macrocyclic complex went to completion in the presence of 0.10 mM La3+ or 0.10 mM Eu3+, 0.10 mM ligand and excess Cu2+ (1.0 mM). The increase in the concentration of Cu(II) macrocycle complex over time is a measure of the inertness of the lanthanide complex to dissociation. For the La(THED)3+ complex, the reaction rate (51) was independent of the concentration of Cu2+, consistent with the following mechanism ... 

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