Hydration Numbers for Lanthanide Ions

For lanthanide complexes with simple ligands, a better understanding of the mode of deexcitation of lanthanide ion excited states can lead to chemical information about the coordination sphere of that metal ion. In particular, techniques have been developed that lead to the determination of the number of water molecules coordinated to the lanthanide ion in the complex.  

For the simple trivalent ions Eu and Tb in aqueous solution, both the luminescence intensity and the excited state lifetime increase when the solvent is D2O rather than This deuterium isotope effect is greater for Eu than it 

From the lifetimes of the excited states of dilute solutions (1 / M) of Eu and Tb in both H2O and D2O, the number of complexed water molecules can be counted. The method has been validated by plotting the difference in reciprocal excited state lifetimes [Ax = (H2O) -(D2O)] against the number of coor- 

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