Recrystallization of Ln(NO3)(3) (Ln = Sm, Eu, Yb) in the presence of 18-crown-6 under aqueous conditions yielded [Ln(NO3)(3)(H2O)(3)]. 18-crown-6. X-ray crystallography revealed isomorphous structures for each of the lanthanide complexes where [Ln(NO3)(3)(H2O)(3)] is involved in hydrogen bonding interactions with 18-crown-6. The transition point where the structural motif changes from [Ln(18-crown-6)(NO3)(3)] (With the metal residing in the crown cavity) to [Ln(NO3)(3)(H2O)(3)]. 18-crown-6 has been identified as at the Nd/Sm interface. A similar investigation involving [Ln(tos)(3)(H2O)(6)] (tos =p-toluenesulfonate) and 18-crown-6 were resistant to crown incorporation. X-ray studies show extensive intra- and intermolecular hydrogen bonding is present.