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

Abstract

Six new three-dimensional (3D) Cd(II) coordination polymers, {[Cd₂(L)₃](NO₃)₄·6H₂O}_n (1), {[Cd₂(L)₃](ClO₄)₄·2H₂O}_n (2), {[Cd₂(L)₃](BF₄)₄·2H₂O}_n (3), {[Cd(L)Cl₂]·2H₂O}_n (4), {[Cd₂(L)₂(SO₄)₂(H₂O)]·2H₂O}_n (5) and {[Cd₂(L)(SO₄)₂(H₂O)₃]·4H₂O}_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 (4⁶·6⁶·8³)₂(4²·6³·8)₃ topology. Complex 4 has a different 3D framework structure with (6⁵·8) 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.