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 Zn 2 LCl 4 ( 1 ), Hg 2 LCl 4 ( 5 ), Hg 2 LBr 4 ( 6 ), and Hg 2 LI 4 ( 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 {[Cd 2 L(μ-Cl) 2 ]Cl 2 } n · n H 2 O ( 2 ) and {[Cd 2 L(μ-Br) 2 ]Br 2 } n · n H 2 O ( 3 ) form pseudo-helix 1-D coordination polymers through Cd−X 2 −Cd (X = Cl, Br) bridges. The compound {[Cd 2 L(μ-I)(μ···I)]I 2 } 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.