The crystal structures and spectral behaviour of benzo-15-crown-5 adducts with hydrated lanthanide picrates

A new series of benzo-15-crown-5 adducts with hydrated lanthanide (La, Pr, Nd, Sm, Eu, Gd, Er) picrates has been obtained. Elemental analyses indicated that their stoichiometry is 1:2:3 (metal:benzo-15-crown-5:picrate) except for the lanthanum adduct. X-ray structural analysis of the Nd, Sm and Er adducts revealed that Nd, Sm or Er ions coordinate directly with water molecules and the picrate anion. The benzo-15-crown-5 acts as a second-sphere ligand which associates with the Nd, Sm or Er ion through hydrogen bonding by coordinating water molecules. From investigation of the IR and UV-vis spectra of the adducts, it can be deduced that the adducts, except lanthanum, exhibit a similar molecular structure to that of the Nd, Sm and Er adducts. These new adducts may also be classified as supermolecules because each is an associate of two chemical species of hydrated lanthanide picrate and benzo-15-crown-5 held together by coordination water molecules. Copyright (C) 1996 Elsevier Science Ltd