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 H2bttpa) links CdII cations, giving rise to the three-dimensional CdII coordination polymer catena-poly[diaqua[μ4-2,5-bis(1H-1,2,4-triazol-1-yl)terephthalato-κ4
O
1:O
4:N
4:N
4′]cadmium(II)], [Cd(C12H6N6O4)(H2O)2]
n
or [Cd(bttpa)(H2O)2]
n
. 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 trans positions and two triazole N atoms in cis positions. Two aqua ligands in cis 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
O
1:O
4 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.
Crystal structure of dirubidium hydrogen citrate from laboratory X-ray powder diffraction data and DFT comparison