Lanthanide Coordination Polymers Constructed from Imidazole-4,5-Dicarboxylate and Sulfate: Syntheses, Structural Diversity, and Photoluminescent Properties

Three series of lanthanide coordination polymers of {[Ln₂(HIDC)₂(SO₄)­(H₂O)₅]·H₂O}_<i>n</i> (CPs-<b>1Ln</b>, Ln = Sm, Eu, Tb, Dy, Ho, Er, and Yb), {(H₂prz)­[Ln₂(HIDC)₂(SO₄)₂]}_<i>n</i> (CPs-<b>2Ln</b>, Ln = Sm and Eu), and [Ln₂(HIDC)₂(SO₄)­(H₂O)₂]_<i>n</i> (CPs-<b>3Ln</b>, Ln = Tb, Dy, Ho, Er, and Yb) have been hydrothermally synthesized by the reactions of Ln­(NO₃)₃·6H₂O with imidazole-4,5-dicarboxylic acid (H₃IDC) and sulfuric acid (H₂SO₄) in the presence of piperazine (prz) at different temperatures. The results of the single-crystal X-ray diffraction analysis reveal that CPs-<b>1Ln</b> presents a three-dimensional (3D) architecture, in which alternating one-dimensional (1D) right-/left-handed helical chains of [Ln₂(HIDC)₂]_∞ are interlinked by μ₃-SO₄^2– anions. CPs-<b>2Ln</b> assumes a H₂prz²⁺ templated 3D anionic layer-pillared metal–organic framework (MOF) of {[Ln₂(HIDC)₂(SO₄)₂]}_<i>n</i>^2<i>n</i>–, in which two-dimensional (2D) (6,3) network layers of [Ln₂(HIDC)₂]_<i>n</i>^2<i>n</i>+ are pillared by μ₂-SO₄^2– anions. CPs-<b>3Ln</b> is a 2D layer structure, in which two 2D (6,3) monolayers of [Ln₂(HIDC)₂(H₂O)₂]_<i>n</i>^2<i>n+</i> are connected by μ₂-SO₄^2– anions to form a 2D double-layer structure. The adjacent 2D double-layers are further stacked together via strong hydrogen bonding interactions to generate a 3D supramolecular framework. In addition, the results of photoluminescent measurements for Sm (<b>1Sm</b> and <b>2Sm</b>), Eu (<b>1Eu</b> and <b>2Eu</b>), Tb (<b>1Tb</b> and <b>3Tb</b>), and Dy (<b>1Dy</b> and <b>3Dy</b>) compounds in the solid state at room temperature indicate that different structural types have a different influence on their characteristic photoluminescences