Syntheses, crystal structure, and luminescence properties of three new Cd(II) polymers based on different conformational carboxylates

Three new coordination polymers, namely, {[Cd3(L1)2(IP)2(H2O)4]}n (1), {[Cd2(L2)2(IP)2]·(CH3OH)(DMF)}n (2) and [Cd(L3)(IP)]n (3) (H3L1 = benzene-1,2,4-tricarboxylic acid, H2L2 = 2,2-bis(4-carboxyphenyl)hexafluoropropane, H2L3 = 1,3-phenylenediacetic acid and IP = 1H-imidazo[4,5-f][1,10]-phenanthroline), were prepared via self-assembly of pharmaceutical agent IP with cadmium sulfate in the presence of the different backbones of carboxylate linkers under mild conditions. All the polymers possess 2D structural motifs. The rigid tricarboxylate ligand links the metal centers to form a tetranuclear core in 1. In 2, the 2D network with trinuclear cores is further extended into 3D supramolecular arrays through aromatic stacking interactions. Interestingly, IP ligand acts in a tridentate mode via the two N atoms of pyridyl rings and the third N atom of imidazole ring and connects metal atoms into 1D zigzag chain in 3. The structural analysis reveals that the backbones of carboxylates have critical effect on the construction of the complexes. Solid-state luminescent spectra of the Cd(II) complexes indicate intense fluorescent emissions.