Synthesis, crystal structure and characterization of a three-dimensional Cd coordination polymer constructed from 2,5-bis(1H-1,2,4-triazol-1-yl)terephthalate.

Bifunctional organic ligands are very popular for the design of coordination polymers because they allow the formation of a great diversity of structures. In the title coordination polymer, the new bifunctional inversion-symmetric ligand 2,5-bis(1H-1,2,4-triazol-1-yl)terephthalic acid (abbreviated as Hbttpa) links Cd cations, giving rise to the three-dimensional Cd coordination polymer catena-poly[diaqua[μ-2,5-bis(1H-1,2,4-triazol-1-yl)terephthalato-κO:O:N:N]cadmium(II)], [Cd(CHNO)(HO)] or [Cd(bttpa)(HO)]. The asymmetric unit consists of half a Cd cation, half a bttpa ligand and one coordinated water molecule. The Cd cation is located on a twofold axis and is hexacoordinated in a distorted octahedral environment of four O and two N atoms. Four different bttpa ligands contribute to this coordination, with two carboxylate O atoms in trans positions and two triazole N atoms in cis positions. Two aqua ligands in cis positions complete the coordination sphere. The fully deprotonated bttpa ligand sits about a crystallographic centre of inversion and links two Cd cations to form a chain in a μ-terephthalato-κO:O bridge. This chain extends in the other two directions via the triazole heterocycles, producing a three-dimensional framework. O-H...O hydrogen bonds and weak C-H...N interactions stabilize the three-dimensional crystal structure. The FT-IR spectrum, X-ray powder pattern, thermogravimetric behaviour and solid-state photoluminescence of the title polymer have been investigated. The photoluminescence is enhanced and red-shifted with respect to the uncoordinated ligand.