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 (H₃mptc), {[Ln(mptc)(H₂O)₄]·3H₂O}_n, [Ln = Pr (1), Nd (2), Sm (3), Tb (4)], have been synthesized by the self-assembly reaction of potassium 6-methyl-2,3,5-pyridinetricarboxylate (K₃mptc) 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 P2₁/n 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 (H₂O)₂ dimers between adjacent water tapes.