Two new CoII coordination polymers with multifunctional 5-amino-2,4,6-tribromoisophthalic acid and flexible isomeric bis(imidazole) ligands: preparation, crystal structure and characterization

Abstract

Two new CoII coordination polymers (CPs), namely, catena-poly[[[(5-amino-2,4,6-tribromobenzene-1,3-dicarboxylato-κO)aquacobalt(II)]-bis[μ-1,3-bis(imidazol-1-ylmethyl)benzene-κ2 N:N′]] 4.75-hydrate], {[Co(C8H2Br3NO4)(C14H14N4)2(H2O)]·4.75H2O} n , (1), and poly[(μ-5-amino-2,4,6-tribromobenzene-1,3-dicarboxylato-κ2 O 1:O 3)[μ-1,2-bis(imidazol-1-ylmethyl)benzene-κ2 N:N′]cobalt(II)], [Co(C8H2Br3NO4)(C14H14N4)] n , (2), have been synthesized successfully by the assembly of multifunctional 5-amino-2,4,6-tribromoisophthalic acid (H2ATBIP) and CoII ions in the presence of the flexible isomeric bis(imidazole) ligands 1,3-bis(imidazol-1-ylmethyl)benzene (mbix) and 1,2-bis(imidazol-1-ylmethyl)benzene (obix). The isomeric mbix and obix ligands have a big influence on the structures of CPs (1) and (2). CP (1) is composed of chains of nanometre-sized elliptical rings, in which the CoII atom exhibits a distorted octahedral coordination geometry and ATBIP2− acts as a monodentate ligand. Two adjacent chains are interlinked by π–π stacking interactions and hydrogen bonds, resulting in a supramolecular double chain. Hydrogen-bonded R 8 6(16) rings extend adjacent supramolecular double chains into a two-dimensional supramolecular layer. Halogen bonding and a hydrogen-bonded R 4 2(8) ring further link the two-dimensional supramolecular layers, leading to the formation of a three-dimensional supramolecular network. The CoII ion in CP (2) is tetracoordinated, exhibiting a distorted tetrahedral configuration. The ATBIP2− ligand exhibits a bis(monodentate) coordination bridging mode, linking adjacent CoII ions into zigzag chains, which are further bridged by the auxiliary bridging obix ligand, resulting in a two-dimensional (4,4) topological network. Interlayer hydrogen and halogen–halogen bonding further extend the two-dimensional layers into a three-dimensional supramolecular network. A detailed analysis of the solid-state UV–Vis–NIR diffuse-reflectance spectra of (1) and (2) indicates that a wide optical band gap exists in both (1) and (2). CP (1) exhibits an irreversible dehydration–rehydration behaviour.