Identification of the structural boundary between [Ln(18-crown-6)(NO3)3] and [Ln(NO3)3(H2O)3] · 18-crown-6 Motifs in the lanthanide Series

Abstract

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.