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.

以镧系离子与新型配体6-甲基-2,3,5-吡啶三甲酸（6-methyl-2,3,5-pyridinetricarboxylic acid，缩写H3mptc）为构筑基元，通过6-甲基-2,3,5-吡啶三甲酸钾（potassium 6-methyl-2,3,5-pyridinetricarboxylate，缩写K3mptc）与稀土盐在水溶液中的自组装反应，成功合成了系列配位聚合物{[Ln(mptc)(H₂O)₄]·3H₂O}ₙ（其中Ln=镨(Pr)（1）、钕(Nd)（2）、钐(Sm)（3）、铽(Tb)（4））。采用X射线单晶衍射分析、元素分析、红外光谱（IR）、荧光光谱及热分析对上述配合物进行了系统表征。该四种配位聚合物为同晶化合物，均结晶于单斜晶系，空间群为P2₁/n。Ln(III)离子与三种不同配位模式的羧酸根配位，通过桥联作用形成无限二维（2D）配位聚合物骨架。在金属晶层之间的空隙中，存在含有褶皱船型六元水环的无限长T6(2)水带。相邻水带之间通过（H₂O）₂二聚体相互作用，自组装形成新颖的二维L6(5)14(8)水层结构。