Self-assembled microporous lanthanide coordination polymers built by 2-hydroxynicotinic acid and oxalate ligands

Two new microporous lanthanide coordination polymers, namely, [Eu(Hnica)2(ox)2(H2O)2] · 5H2O (1) and [Gd(Hnica)2(ox)2(H2O)2] · 5H2O (2), have been successfully synthesized by reaction of 2-hydroxynicotinic acid (H2nica) in the presence of the coligand oxalate (ox) with lanthanide ions under hydrothermal conditions. Single crystal X-ray diffraction analyses reveal that compounds 1 and 2 are isostructural and exhibit two-dimensional (2D) layer architectures built by the linkage of 1D Ln–ox chains with μ2- Hnica bridging ligands, which are further connected by strong π–π stacking interactions to form 3D microporous supramolecular frameworks. Furthermore, the thermal stability and solid-state luminescent behavior of compound 1 were also investigated.