Tuning structural topologies of five photoluminescent Cd(II) coordination polymers through modifying the substitute group of organic ligand

Five new Cd(II) coordination polymers based on mixed 5-position substituted 1,3-benzenedicarboxylate ligands (R=NO2/OH/CH3) and 1,4-bis(imidazol-1-yl)benzene (L1)or 1,4-bis(1-imidazol-yl) -2,5- dimethyl benzene (L2), namely [Cd(5-NO2-ip)(L1)·H2O] (1), [Cd(5-OH-ip)(L1)]n (2), [Cd(5-NO2-ip) (L1)0.5(H2O)2]n (3), {[Cd(5-NO2-ip)(L2)0.5(H2O)]·H2O} (4), [Cd(5-CH3-ip)(L2)(H2O)2]n (5), have been synthesized hydrothermally and structurally characterized. With different substituted groups in the organic ligands, five compounds exhibit five distinct framework structures. By changing the pH value, compound 1 with 2-fold interpenetrating (4,4)-layer structure and compound 3 with three-dimensional diamond-type framework are obtained, respectively, from the assembly of Cd(NO3)2·4H2O, 5-NO2-ip and L1 ligand. The replacement of 5-NO2-ip with 5-OH-ip leads to a compound 2 which features a doubly pillared layered structure with pcu topology. Compounds 4 and 5 are constructed from L2 ligand with 5-NO2-ip or 5-CH3-ip, respectively. Compound 4 has non-interpenetrating (4,4) layer, while compound 5 shows unusual 2D->3D polycatenation of bilayers. The results reveal a new approach toward tuning structural topologies of coordination polymers through modifying the substitute groups in organic ligands. Furthermore, the photoluminescent properties of compounds 1–5 have been studied in the solid state at room temperature.