Zinc and cadmium coordination polymers assembled with 2,2′-bipyridine and bithiophenedicarboxylic acid: Effect of metal ions on the conformation of ligand

Two novel metal–organic coordination polymers with the formulas [Zn(btdc)(2,2′-bpy)]n (1) and {[Cd2(btdc)2(2,2′-bpy)]·DMF}n (2) have been solvothermally synthesized by the assembly of mixed ligands, H2btdc and 2,2′-bpy with Zn(NO3)2·6H2O and Cd(NO3)2·4H2O, respectively, where H2btdc = 2,2′-bithiophene-5,5′-dicarboxylic acid, 2,2′-bpy = 2,2′-bipyridine, and DMF = N,N′-dimethylformamide. Complex 1 is composed with one-dimensional (1D) infinite zigzag polymeric coordination chains, which are further stacked into 3D supramolecular architecture by π–π stacking interaction. Complex 2 possesses 2D layers with the thickness about 1.2 nm, these layers forming a 3D network through π–π stacking interactions. In complex 1, the btdc ligand exists in stable trans conformation and the conformation of btdc ligand in complex 2 is of both trans and cis. Furthermore, these two complexes show enhanced fluorescent emission in comparison with H2btdc ligand.

Graphical abstractTwo coordination polymers were synthesized using bithiophenedicarboxylic acid (H2btdc) and 2,2′-bipyridine ligands. The btdc ligand exists in stable trans conformation in Zn-based complex, and both trans and unusual cis conformations in Cd-based complex. The properties of metal ion are important to tune the conformations of btdc ligand.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Two coordination polymers were synthesized using H2btdc and 2,2′-bpy ligands. ► The unusual cis conformation of btdc ligand was existed in Cd-based complex. ► The properties of metal ion are important to tune the conformations of btdc ligand. ► These two complexes show enhanced fluorescent emission in comparison with ligand.