Cadmium(II) coordination polymers with flexible tetradentate ligand 1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene: anion effect and reversible anion exchange property

Six new three-dimensional (3D) Cd(II) coordination polymers, {[Cd-2(L)(3)](NO3)(4)center dot 6H(2)O}(n) (1), {[Cd-2(L)(3)](ClO4)(4)center dot 2H(2)O}(n) (2), {[Cd-2(L)(3)](BF4)(4)center dot 2H(2)O}(n) (3), {[Cd(L)Cl-2]center dot 2H(2)O}(n) (4), {[Cd-2(L)(2)(SO4)(2)(H2O)]center dot 2H(2)O}(n) (5) and {[Cd-2(L)(SO4)(2)(H2O)(3)]center dot 4H(2)O}(n) (6), have been solvothermally synthesized by reactions of the corresponding Cd( II) salts with flexible tetradentate ligand 1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene (L), respectively. The X-ray diffraction analysis revealed that the isostructural 1, 2 and 3 have 3D framework structures with (4(6).6(6).8(3))(2)(4(2).6(3).8)(3) topology. Complex 4 has a different 3D framework structure with (6(5).8) topology, while 5 and 6 possess pillared-layer and plywood-like 3D framework structures, respectively. The distinct structures of 1 (2, 3), 4 and 5 indicate that the counter anions with different coordination abilities play an important role in the formation of coordination polymers. Complexes 5 and 6, synthesized by the same reactants in the same solvent, have different structures due to the different metal/ligand ratio. In addition, the results also demonstrated that the flexible tetradentate ligand L can adopt varied conformations and coordination modes to form complexes with different structures. L adopts up, up, down, down-conformation in 1-3, while in 4, it has a up, down-conformation. It is interesting that two different conformations of up, down, down, up- and H-type of L coexist in 5. In the case of 6, L has H-type conformation. Furthermore, the reversible anion exchange property of 1 was studied.