(C₄N₂H₁₂)₃[Ln₃(OH)(SO₄)₇] (Ln = Sm, Eu, and Tb): A Series of Honeycomb-like Open-Framework Lanthanide Sulfates with Extra-Large Channels Containing 24-Membered Rings

Three novel organic amine templated honeycomb-like lanthanide sulfates, (C₄N₂H₁₂)₃­[Ln₃­(OH)­(SO₄)₇] (Ln = Sm (<b>1</b>), Eu (<b>2</b>), and Tb (<b>3</b>)), with extra-large channels containing 24-membered rings (24MR) have been synthesized by using chair form piperazine as the structure-directing agent under one-pot solvothermal reactions. The three compounds are isostructural, and the open framework of the title compounds is the first lanthanide sulfate example with extra-large channels containing 24MR. It has an <i><b>acs</b></i> framework topology. The three compounds are strong luminescent materials that display characteristic Sm³⁺, Eu³⁺, and Tb³⁺ emission bands in the visible region. The observed second-harmonic generation efficiencies of the three compounds are all 0.4 times that of urea. TGA profiles and XRD measurements demonstrate their high thermal stability