Excitation Spectra of Geometric Isomers

Isomeric forms of Eu(III) complexes may give rise to multiple excitation peaks if the Eu(III) coordination sphere is sufficiently different. For example, Eu(TCMC) [refer to Fig. 8.5 for this and other Ln(macrocycle) stmctures] has two different diastereomeric forms in solution that result from distinct orientations of pendent groups and macrocyclic ring (Fig. 8.6) [44,45]. Note that the Ln(ni) complexes are specified without water ligands [e.g. Eu(TCMC)] unless a particular coordination complex species is discussed [e.g. Eu(TCMC)(OH2)]. 

Another more familiar example of two isomeric forms in solution is Eu(EDTA) (Fig. 8.3a). The two different excitation peaks purportedly arise from Eu(EDTA) complexes with two different coordination numbers, one with two water hgands and one with three ligands. This assignment is based in part on the equilibrium behaviour of the two species as a function of pressure [48,49]. 

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