Two- and three-dimensional lanthanide complexes: Synthesis, crystal structures, and properties

3,5-Pyrazoledicarboxylic acid (H3L) reacts with nitrate salts of lanthanide(III) (Ln = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er) under hydrothermal conditions to form a series of lanthanide polymers 1-9. These nine polymers have the same crystal system of monoclinic, but they exhibit three different kinds of metal-organic framework structures. The complexes {[Ln(2)(HL)(3)(H2O)(4)]center dot 2H(2)O}(n) (Ln = Pr (1), Nd (2), and Sm (3)) were isostructural and exhibited porous 3D frameworks with a Cc space group. The complexes {[Ln(2)(HL)(3)(H2O)(3)]center dot 3H(2)O}(n) (Ln = Eu (4), Gd (5), and Tb (6)) were isostructural and built 2D double-decker (2DD) frameworks with a P2(1)/c space group. The complexes {[Ln(HL)(H2L)(H2O)(2)]}(n) ((Ln = Dy (7), Ho (8), and Er (9)) were also isostructural and formed 2D monolayer (2DM) frameworks with a P2(1)/n space group. The structure variation from the 3D porous framework to the 2D double-decker to the 2D monolayer is attributed to the lanthanide contraction effect. Notably, six new coordination modes of 3,5-pyrazoledicarboxylic acid were observed, which proved that 3,5-pyrazoledicarboxylic acid may be used as an effective bridging ligand to assemble lanthanide-based coordination polymers. The photophysical and magnetic properties have also been investigated.