A Series of Three-Dimensional Lanthanide Coordination Polymers with Rutile and Unprecedented Rutile-Related Topologies

The complexes of formulas Ln(pydc)(Hpydc) (Ln = Sm (1), Eu (2), Gd (3); H₂pydc = pyridine-2,5-dicarboxylic acid) and Ln(pydc)(bc)(H₂O) (Ln = Sm (4), Gd (5); Hbc = benzenecarboxylic acid) have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR, TG analysis, and single-crystal X-ray diffraction. Compounds 1−3 are isomorphous and crystallize in the orthorhombic system, space group Pbcn. Their final three-dimensional racemic frameworks can be considered as being constructed by helix-linked scalelike sheets. Compounds 4 and 5 are isostructural and crystallize in the monoclinic system, space group P2₁/c. pydc ligands bridge dinuclear lanthanide centers to form the three-dimensional frameworks featuring hexagonal channels along the a-axis that are occupied by one-end-coordinated bc ligands. From the topological point of view, the five three-dimensional nets are binodal with six- and three-connected nodes, the former of which exhibit a rutile-related (4.6²)₂(4²·6⁹·8⁴) topology that is unprecedented within coordination frames, and the latter two species display a distorted rutile (4.6²)₂(4²·6¹⁰·8³) topology. Furthermore, the luminescent properties of 2 were studied.