Synthesis, crystal structure and characterization of a three‐dimensional CdII coordination polymer constructed from 2,5‐bis(1<italic>H</italic>‐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(1<italic>H</italic>‐1,2,4‐triazol‐1‐yl)terephthalic acid (abbreviated as H2bttpa) links CdII cations, giving rise to the three‐dimensional CdII coordination polymer <italic>catena</italic>‐poly[diaqua[μ4‐2,5‐bis(1<italic>H</italic>‐1,2,4‐triazol‐1‐yl)terephthalato‐κ4<italic>O</italic>1:<italic>O</italic>4:<italic>N</italic>4:<italic>N</italic>4′]cadmium(II)], [Cd(C12H6N6O4)(H2O)2]<italic>n</italic> or [Cd(bttpa)(H2O)2]<italic>n</italic>. The asymmetric unit consists of half a CdII cation, half a bttpa2− ligand and one coordinated water molecule. The CdII cation is located on a twofold axis and is hexacoordinated in a distorted octahedral environment of four O and two N atoms. Four different bttpa2− ligands contribute to this coordination, with two carboxylate O atoms in <italic>trans</italic> positions and two triazole N atoms in <italic>cis</italic> positions. Two aqua ligands in <italic>cis</italic> positions complete the coordination sphere. The fully deprotonated bttpa2− ligand sits about a crystallographic centre of inversion and links two CdII cations to form a chain in a μ2‐terephthalato‐κ2<italic>O</italic>1:<italic>O</italic>4 bridge. This chain extends in the other two directions <italic>via</italic> 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. [ABSTRACT FROM AUTHOR]