Microporous Rare Earth Coordination Polymers:  Effect of Lanthanide Contraction on Crystal Architecture and Porosity

A series of microporous coordination polymers of adipic (H2ad) and pimelic acids (H2pim) with rare earth metals have been synthesized and structurally characterized. In the case of adipic acid, two distinct structure types were isolated:  structure type I with formula [Ln2(ad)3(H2O)4]6H2O, Ln = Ce3+, Pr3+, Nd3+, and strucure type II with formula [Ln2(ad)3(H2O)4]xH2O, Ln = Nd3+, Sm3+, Gd3+, Er3+, Yb3+. Type I compounds are isostructural to lanthanum adipate (Inorg. Chem. 1998, 37, 3407) and contain interconnected channels filled with hydrogen-bonded water molecules. The structure of type II polymers consists of interpenetrated (4,4) metal−organic networks. Channels along one crystallographic direction are created by the interpenetration. The minimum width of the channels depends on the nature of the metal incorporated in the framework. The passage from type I to type II structure is ascribed to the well-known effect of lanthanide contraction. In the case of H2pim, one compound of formula [La(pim)(Hpim)(H2O)]H2O was isolated. Channels, filled with water molecules, are formed along one crystallographic direction. In all compounds, the water molecules can be reversibly removed.