Structures and equilibria involving the [222] cryptand and europium ions

Complexes of Eu(III) salts and the [222] cryptand show in methanol the presence of at least three species, interconverting slowly on the NMR time scale. Shift changes of up to 75 ppm and line widths of up to 110 Hz characterize the inner sphere complexes, which differ significantly in symmetry. In water at pH 7 there is no stable complex at all; if one dissolves the solid complex, which holds the metal inside the cavity as evidenced from a published solid state analysis, a rapid decay to the protonated ligand is observed, with a rate constant of 8.7×10−4 s−1.