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

Three new Cd(II) coordination polymers, [Cd(hbdmbm)(SO4)](n) (1), {[Cd-3(hbdmbm)(4)(5-SSPIA)(2)]center dot(H2O)(2)}(n). (2) and [Cd-3(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 I 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 Schlafli symbol of (6(3))(2)(6(5).8)(6(8).8(2))(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 20 layer with polygon geometry, in which 5-SSPIA anions act as three-connected nodes. Complex 3 shows more complicated 3D framework with Schlafli symbol (4.6(4)-8)(4-8(2))(4(2-).5(3).6(3).7.8)(4(2).5(3).6)(5-6.7-8(2).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. (C) 2012 Elsevier Ltd. All rights reserved.