Structures and Photoluminescence Properties of Four Cadmium(II) Coordination Polymers Synthesized by Rigid Ligands and N-Donor Ligands

Abstract

Four metal–organic coordination polymers, [Cd2(dna)2(2,2′-bpy)2]n (1), {[Cd4(dna)4(im)3]·5H2O}n (2), {[Cd2(dna)2(4,4′-bpy)(H2O)2]·2EtOH}n (3), and {[Cd4(dna)4(1,3-dpp)4(H2O)4]·2H2O}n (4) (H2dna = 4,6-dimethyl-5-nitroisophthalic acid; 2,2′-bpy = 2,2′-bipyridine; im = imidazole; 4,4′-bpy = 4,4′-bipyridine; 1,3-dpp = 1,3-di(4-pyridyl)propane; and EtOH = ethanol, have been solvothermally synthesized and characterized. Compound 1 displays a one-dimensional (1D) ladder structure and the neighbouring ladders are further stabilized by π···π interactions to form a two-dimensional (2D) layer. Compound 2 forms a 2D layer based on infinite 1D [Cd2(COO)4]n chain and the im ligands act as terminal ligands, preventing expansion of the dimensionality. Compound 3 features a 2D 44-sql layer based on binuclear [Cd2(COO)4] secondary building units as 4-connected nodes, and is further linked to be an unusual three-dimensional (3D) supramolecular architecture by hydrogen bonds involving the coordinated water molecules, carboxylate groups, and lattice ethanol molecules. Compound 4 possesses a 2-fold interpenetrated dia net. The diverse structures and topologies of compounds 1–4 indicate that the N-containing ligands have significant effects on the formation of the final network structures. In addition, the thermal stabilities, structure comparison, and photoluminescence properties of the complexes have been investigated.