Formation of the Water Layer in Lanthanide Coordination Polymers with 6-Methyl-2,3,5-Pyridinetricarboxylate as a Novel Bridging Ligand

Four coordination polymers with lanthanide ions and the novel ligand 6-methyl-2,3,5-pyridinetricarboxylic acid (H<sub>3</sub>mptc), {[Ln(mptc)(H<sub>2</sub>O)<sub>4</sub>]·3H<sub>2</sub>O}<sub><i>n</i></sub>, [Ln = Pr (<b>1</b>), Nd (<b>2</b>), Sm (<b>3</b>), Tb (<b>4</b>)], have been synthesized by the self-assembly reaction of potassium 6-methyl-2,3,5-pyridinetricarboxylate (K<sub>3</sub>mptc) and rare earth salts in aqueous solution. The complexes were characterized by X-ray diffraction single crystal structure analysis, elemental analysis, IR, fluorescence and thermal analysis. The four coordination polymers are isotypics and crystallize in the monoclinic system with the <i>P</i>2<sub>1</sub>/<i>n</i> space group. The Ln(III) ions are coordinated by three carboxylate groups with different coordination modes and link to form an infinite two-dimensional (2D) polymer. Infinite T6(2) water tapes containing puckered-boat hexameric water rings exist in the space between the metal crystal building layers. The T6(2) water tapes self-assemble into novel 2D L6(5)14(8) water layers through (H<sub>2</sub>O)<sub>2</sub> dimers between adjacent water tapes.