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 (<b>1</b>), Nd (<b>2</b>), Sm (<b>3</b>), CDA = 4-hydroxypyran-2,6-dicarboxylate), [Ho(CDA)(H<sub>2</sub>O)] (<b>4</b>), [Pr(HCDA)(C<sub>2</sub>O<sub>4</sub>)<sub>0.5</sub>(H<sub>2</sub>O)<sub>2</sub>] (<b>5</b>), [Lu(CDA)Ba<sub>2</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]·0.25CH<sub>3</sub>OH (<b>6</b>), [Dy(HCAM)<sub>2</sub>(CAM)Ba<sub>2</sub>(H<sub>2</sub>O)<sub>9.75</sub>]·7.625H<sub>2</sub>O ((<b>7</b>), CAM = 4-hydroxypyridine-2,6-dicarboxylate), [Sm<sub>2</sub>(CAM)<sub>4</sub>Ba<sub>3</sub>(H<sub>2</sub>O)<sub>2</sub>] (<b>8</b>), have been synthesized under hydrothermal conditions. They were structurally characterized by single-crystal X-ray diffraction. Compounds <b>1</b>−<b>3</b> are isostructural and display novel three-dimensional (3D) architectures, and compound <b>4</b> features a two-dimensional (2D) double-layer structure. The structural divergence between <b>1</b>−<b>3</b> and <b>4</b> may originate from a lanthanide contraction effect. By increasing the temperature during the synthesis of <b>1</b>, CDA was partly decomposed into oxalate ions, and as a result, compound <b>5</b> with a 3D framework different from that of <b>1</b> was obtained. The Lu-based compound isostructural to <b>4</b> has not been obtained so far under synthetic conditions similar to that of <b>1</b>−<b>4</b>. However, by replacing LiOH with Ba(OH)<sub>2</sub>, heterometallic [LuBa] compound <b>6</b> was successfully synthesized, exhibiting a 3D framework. After changing CDA into CAM based on the synthesis of <b>6</b>, compounds <b>7</b> with a one-dimensional (1D) chain and <b>8</b> with a sandwich-like 3D structure were produced. Luminescence analyses were performed on compounds <b>7</b> and <b>8</b>, which exhibit the characteristic transitions of corresponding lanthanide ions. The magnetic susceptibilities of <b>5</b> and <b>7</b> were measured and discussed.