Structural diversity and fluorescent properties of CdII coordination polymers with 5-halonicotinates regulated by solvent and ligand halogen-substituting effect

Seven Cd-II coordination polymers have been prepared from CdCl2 and 5-halonicotinic acids (HL-X, X = F or Cl) in different solvent media using a similar layered diffusion method. A pair of polymorphic isomers [Cd(L-F)(2)](n) (1 and 2) can be assembled from CH3CN-H2O and CH3OH-H2O systems, respectively, featuring the 3-D (3,5)-connected (4.6(2))(4.6(7).8(2)) network (5-connected node for each Cd-II ion and 2- or 3-connected linker for the two different types of L-F- ligand) and the 3-D (3,6)-connected ant framework with the point symbol of (4.6(2))(2)(4(4).6(2).8(8).10). While in DMF-H2O solvent, a 2-D layered complex [Cd(L-F)Cl(DMF)](n) (3) is obtained with the (3,5)-connected net of (3.4.5)(3(2).4.5.6(2).7(4)) topology, where the chloride anion is involved in coordination. When the HL-Cl ligand is utilized instead of HL-F, the assembling reactions in CH3CN-H2O and DMF-H2O media lead to the 3-D (3,5)-connected network of [Cd(L-Cl)(2)](n) (4) and the 2-D (3,5)-connected net of [Cd(L-Cl)Cl(DMF)](n) (6), which are isostructural to complexes 1 and 3, respectively. [Cd(L-Cl)(2)(H2O)(2)](n) (5) can be generated from the CH3OH-H2O medium, showing a 2-D (4,4) layered structure, and the similar reaction in the C2H5OH-H2O solvent will produce a 3-D coordination framework {[Cd(L-Cl)(2)(H2O)(0.5)](C2H5OH)(0.75)(H2O)(0.25)}(n) (7) with the (3,6)-connected (3.4.5)(3(2).4(4).5(5).6(2).7(2)) net. These structural divergences can be ascribed to the significant solvent modulation and halogen-substituting effect of 5-halonicotinates. Furthermore, their solid-state properties such as thermal stability and fluorescence have also been investigated.