A Series of Lanthanide Secondary Building Units Based Metal−Organic Frameworks Constructed by Organic Pyridine-2,6-Dicarboxylate and Inorganic Sulfate.

A series of novel lanthanide coordination polymers constructed from organic pyridine-2,6-dicarboxylate (2,6-pydc) and inorganic sulfate, namely, [Eu3(2,6-pydc)3(2,6-Hpydc)(SO4)(H2O)3·(H2O)3] (1), [Ln2(2,6-pydc)2(SO4)(H2O)2·(H2O)2] (Ln = Ce (2); Ln = Pr (3); Ln = Nd (4); Ln = Sm (5)), and [Ce5(2,6-pydc)6(SO4)2(H2O)3·(Me2NH2)] (6), have been synthesized under hydrothermal conditions. X-ray crystal structure analyses reveal that these compounds have a rich structural chemistry. Compound 1presents a four-connected two-dimensional (2D) network based on hexanuclear {Eu6} secondary building units (SBUs). The 2D layers are further linked into a three-dimensional (3D) supramolecular framework via strong π−π stacking interactions of the pyridyl rings. Compounds 2−5are isostructural and adopt uninodal six-connected 3D framework of pcutopology constructed from square-planar tetranuclear {Ln4} SBUs. Of particular interest is that compound 6exhibits a protonated (Me2NH2)뗩ꦕꭞ binodal (4,6)-connected 3D anionic framework with (42510728)(4254) topology, when the Ce(3) monomer and the planar tetranuclear {Ce4} SBUs are regarded as four-connected and six-connected nodes, respectively. Notably, sulfate serves as an auxiliary supporting bridge to strengthen the {Ln4} or {Ln6} SBUs in these compounds. Compound 1displays intense red luminescence and exhibits the characteristic transition of the Eu3誉. The magnetic properties of 1, 4, and 5reveal the weak antiferromagnetic characters. Furthermore, infrared (IR), thermogravimetric analysis (TGA), elemental analyses (EA), and powder X-ray diffraction (PXRD) properties of these compounds are also studied. [ABSTRACT FROM AUTHOR]