Fabrication and Properties of Eight Novel Lanthanide−Organic Frameworks Based on 4-Hydroxypyran-2,6-dicarboxylate and 4-Hydroxypyridine-2,6-dicarboxylate

Eight novel lanthanide−organic frameworks, [Ln(CDA)] (Ln = Pr (1), Nd (2), Sm (3), CDA = 4-hydroxypyran-2,6-dicarboxylate), [Ho(CDA)(H₂O)] (4), [Pr(HCDA)(C₂O₄)_0.5(H₂O)₂] (5), [Lu(CDA)Ba₂(C₂O₄)₂(H₂O)₂]·0.25CH₃OH (6), [Dy(HCAM)₂(CAM)Ba₂(H₂O)_9.75]·7.625H₂O ((7), CAM = 4-hydroxypyridine-2,6-dicarboxylate), [Sm₂(CAM)₄Ba₃(H₂O)₂] (8), have been synthesized under hydrothermal conditions. They were structurally characterized by single-crystal X-ray diffraction. Compounds 1−3 are isostructural and display novel three-dimensional (3D) architectures, and compound 4 features a two-dimensional (2D) double-layer structure. The structural divergence between 1−3 and 4 may originate from a lanthanide contraction effect. By increasing the temperature during the synthesis of 1, CDA was partly decomposed into oxalate ions, and as a result, compound 5 with a 3D framework different from that of 1 was obtained. The Lu-based compound isostructural to 4 has not been obtained so far under synthetic conditions similar to that of 1−4. However, by replacing LiOH with Ba(OH)₂, heterometallic [LuBa] compound 6 was successfully synthesized, exhibiting a 3D framework. After changing CDA into CAM based on the synthesis of 6, compounds 7 with a one-dimensional (1D) chain and 8 with a sandwich-like 3D structure were produced. Luminescence analyses were performed on compounds 7 and 8, which exhibit the characteristic transitions of corresponding lanthanide ions. The magnetic susceptibilities of 5 and 7 were measured and discussed.