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 center dot center dot center dot X interactions, affording one-dimensional chains. The complexes {[Cd2L(mu-Cl)(2)]Cl-2}(n)center dot nH(2)O ( 2) and {[Cd2L(mu-Br)(2)]Br-2}(n)center dot nH(2)O (3) form pseudo-helix 1-D coordination polymers through Cd-X-2-Cd (X=Cl, Br) bridges. The compound {[Cd2L(mu-I)(mu center dot center dot center dot 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 pi-pi 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.