Structure-directing role of anionic ligands in the assembly of Cd(II) coordination polymers based on SO42−/3,5-dicarboxybenzenesulfonate and flexible bis(benzimidazole) derivatives

Abstract

Three new Cd(II) coordination polymers, [Cd(hbdmbm)(SO4)]n (1), {[Cd3(hbdmbm)4(5-SSPIA)2]·(H2O)2}n (2) and [Cd3(bbdmbm)4(5-SSPIA)2]n (3), based on different O-containing anionic ligands and flexible bis(benzimidazole) derivatives (hbdmbm=1,1′-(1,6-hexanediyl)bis(5,6-dimethylbenzimidazole), bbdmbm=1,1′-(1,4-butanediyl)bis(5,6-dimethylbenzimidazole), 5-SSPIA=sodium 3,5-dicarboxybenzenesulfonate), have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Structure analysis illustrates that complex 1 possesses a 2D (4, 4) network constructed from the binuclear [Cd(SO4)]2 secondary building unit (SBU) and the hbdmbm. Complex 2 shows a 2D/3D crossed 3D framework with Schläfli symbol of (63)2(65·8)(68·82)2. In 2, Cd(II) ions are connected by hbdmbm ligands to construct a 3D framework showing a topological octagon geometry, and also linked by 5-SSPIA to construct a 2D layer with polygon geometry, in which 5-SSPIA anions act as three-connected nodes. Complex 3 shows more complicated 3D framework with Schläfli symbol (4·64·8)(4·82)(42·53·63·7·8)(42·53·6)(5·6·7·82·9), which contains two kinds of SBUs built by 5-SSPIA and bbdmbm. 5-SSPIA anions act as three-connected nodes and four-connected nodes in 3. The structure-directing role of anionic ligands and the effects of conformations of N-donor ligands on the final structures are discussed. In addition, fluorescence properties of complexes 1–3 are also reported in this paper.