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

Complexes of Eu(III) salts and the [222] cryptand show in methanol the pres ence of at least three species, interconverting slowly on the NMR time scal e. Shift changes of up to 75 ppm and line widths of up to 110 Hz characteri ze the inner sphere complexes, which differ significantly in symmetry. In w ater 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 publis hed solid state analysis, a rapid decay to the protonated ligand is observe d, with a rate constant of 8.7x10(-4) s(-1). (C) 2000 Elsevier Science Ltd. All rights reserved.