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

Abstract

Seven CdII 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 (4·62)(4·67·82) network (5-connected node for each CdII 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 (4·62)2(44·62·88·10). 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)(32·4·5·62·74) 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)(32·44·55·62·72) 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.