A series of new lanthanide fumarates displaying three types of 3-D frameworks.

A series of lanthanide fumarates [Sm2(fum)3(H2fum)(H2O)2] (1, H2fum = fumaric acid), [Ln2(fum)3-(H2O)4]·3H2O {Ln = Tb (2a), Dy (2b)} and [Ln2(fum)3(H2O)4] {Ln = Y (3a), Ho (3b), Er (3c), Tm (3d)} were prepared by the hydrothermal method and their structures were classified into three types. The 3-D framework of compound 1 contains a 1-D infinite [Sm-O-Sm]n chain built up from the connection of SmO8(H2O) polyhedra sharing edges via three -COO group bridges of fumarate ligands, which is further constructed into a 3-D network structure with three kinds of fumarate ligands. Compounds 2a-b are isostructural and consist of a 3-D porous framework with 0-D cavities for the accommodation of chair-like hexameric (H2O)6 clusters. Compounds 3a-d are isostructural and have a 3-D network structure remarkably different from those of 1 and 2a-b, due to the different coordination numbers for the Ln(3+) ions and distinct fumarate ligand bridging patterns. A systematic investigation of seven lanthanide fumarates and five reported compounds revealed that the well-known lanthanide contraction has a significant influence on the formation of lanthanide fumarates. The magnetic properties of compounds 1, 2b and 3b-3d were also investigated.