Series of anion-directed lanthanide-rigid-flexible frameworks: syntheses, structures, luminescence and magnetic properties

Abstract

A series of novel self-assembly lanthanide coordination polymers formulated as {[Ce2(pyda)2(μ4-SO4)·5H2O]·2H2O}n (1), {[Gd2(Hpimda)2(μ4-C2O4)·4H2O]·2H2O}n (2), {[Sm4(pyda)2(μ4-C2O4)4·8H2O]·6H2O}n} (3), and {[Gd2(pyda)(μ4-C2O4)2·4H2O]·3H2O}n (4), (H3pimda = 2-propyl-4,5-imidazole-dicarboxylic acid, H2pyda = 2,6-pyridine-dicarboxylic acid) have been synthesized from the reactions of H3pimda or H2pyda with lanthanide salts in the presence of different anions, and were characterized by elemental analysis, IR spectroscopy and X-ray single-crystal diffraction. Compound 1 is a 2D hybrid in which Ce3+ ions are doubly linked by a carboxylate group of the pyda2− ligand. Complexes 2, 3 and 4 have 3D framework structures fabricated through two alternately arranging hexanuclear Ln3+ motifs, among which the guest water molecules are trapped in the 1D tunnel. In 3 and 4, the [Ln2(pyda)2]n layers also consist of alternate left- and right helical chains. Both complexes 2 and 4 exhibit the robust network based on the hexadimeric subunits as 3,3-connected nodes. The emission spectra of the complexes vary depending on which lanthanide ion is present and the aromatic ligands. In addition, compound 1 exhibits weak but significant ferromagnetic couplings between the Ce(III) ions through carboxylato bridges, while dominant antiferromagnetic interactions were observed in compounds 2, 3 and 4.