(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 (1), Eu (2), and Tb (3)), 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 acs 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.