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.