Syntheses, Crystal Structures, and Photoluminescent Properties of a Series of M(II) Coordination Polymers Containing M−X₂−M Bridges: From 1-D Chains to 2-D Networks

The novel blue-purple luminescent bridging ligand <i>N</i>,<i>N</i>,<i>N</i>‘,<i>N</i>‘-tetrakis(2-pyridyl)-2,6-pyridinediamine (<b>L</b>) has been synthesized. The coordination of this ligand with a series of Zn(II), Cd(II), and Hg(II) salts has been investigated. Seven new complexes (<b>1</b>−<b>7</b>) were obtained and characterized by elemental analyses and single-crystal X-ray analyses. In the compounds Zn₂LCl₄<b></b>(<b>1</b>), Hg₂LCl₄<b></b>(<b>5</b>), Hg₂LBr₄<b></b>(<b>6</b>), and Hg₂LI₄ (<b>7</b>), each ligand is coordinated to two metal ions, forming dinuclear moieties, which are further connected via weak intermolecular M···X interactions, affording one-dimensional chains. The complexes {[Cd₂L(μ-Cl)₂]Cl₂}<i>_n</i>·<i>n</i>H₂O (<b>2</b>) and {[Cd₂L(μ-Br)₂]Br₂}<i>_n</i>·<i>n</i>H₂O (<b>3</b>) form pseudo-helix 1-D coordination polymers through Cd−X₂−Cd (X = Cl, Br) bridges. The compound {[Cd₂L(μ-I)(μ···I)]I₂}<i>_n</i> (<b>4</b>) forms a zigzag 1-D motif with two kinds of Cd−I−Cd bridges. Furthermore, the 1-D chains in all these complexes are connected by face-to-face π−π stacking interactions, affording 2-D networks with various structural geometries<b>.</b> All of these complexes are luminescent in the solid state, with the emission maxima varying in the visible light region within the range of 440−520 nm.