Synthesis, structure, and luminescence of a coordination polymer from fumaropimaric acid and a water cluster

Using fumaropimaric acid (H₃L) as the ligand, a coordination polymer {[Cd(H₂L)₂(H₂O)₂]·8H₂O}_n was synthesized under solvothermal conditions and characterized by elemental analysis, IR, and single-crystal X-ray diffraction. In the complex, Cd(II) is eight-coordinate with a distorted dodecahedral CdO₈ geometry. There is a Cd₂L₂ chelate ring, which forms an infinite 1-D chain structure along the b axis. The 1-D chains are further linked by strong O–H···O hydrogen bonding of a water cluster to form a 2-D structure. A dodecamer water cluster consisting of a five-membered ring with envelope conformation is the first reported. The complex is the first example showing three completely different coordination modes of carboxyl groups for Cd(II) complexes. The complex displayed medium fluorescence emission peaks at ca. 442 nm.