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 N,N,N‘,N‘-tetrakis(2-pyridyl)-2,6-pyridinediamine (L) 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 (1−7) were obtained and characterized by elemental analyses and single-crystal X-ray analyses. In the compounds Zn₂LCl₄(1), Hg₂LCl₄(5), Hg₂LBr₄(6), and Hg₂LI₄ (7), 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}_n·nH₂O (2) and {[Cd₂L(μ-Br)₂]Br₂}_n·nH₂O (3) form pseudo-helix 1-D coordination polymers through Cd−X₂−Cd (X = Cl, Br) bridges. The compound {[Cd₂L(μ-I)(μ···I)]I₂}_n (4) 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. 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.