Entangled Zn(ii)/Cd(ii) coordination complexes based on a flexible bis(methylbenzimidazole) ligand and different dicarboxylates

Abstract

Eight entangled coordination complexes, formulated as [M(hbmb)_0.5(o-phda)]_n [M = Zn (1), Cd (2)], {[M(hbmb)(p-phda)]·H₂O}_n [M = Zn (3), Cd (4)], [M(hbmb)_0.5(oba)]_n [M = Zn (5), Cd (6)], {[M(hbmb)(sdba)]_m}_n [M = Zn, m = 2 (7); m = 1, Cd (8)] (H₂phda = phenylenediacetic acid, H₂oba = 4,4′-oxybis(benzoic acid), H₂sdba = 4,4′-sulfonyldibenzoic acid), have been prepared by hydrothermal reactions of the flexible ligand 1,1′-(1,6-hexane)bis-(2-methylbenzimidazole)) (hbmb) with metal ions in the presence of various dicarboxylate coligands. Isostructural complexes 1 and 2 reveal 6-connected self-penetrating three-dimensional (3D) frameworks with (4⁴·6¹⁰·8)-roa topologies. 3 and 4 display 4-fold interpenetrating 3D frameworks with 6⁶-dia topologies. 5 and 6 exhibit 3D 2-fold interpenetrating 6-connected frameworks with (4¹²·6³)-pcu topologies. Both 7 and 8 are 3D frameworks constructed through unusual 2D → 3D parallel interpenetration of corrugated 2D (4,4) nets, of which 7 shows a 4-connected (4⁴·6²)₂ topology and 8 presents a 4-connected 4⁴·6² topology. A systematic structural comparison of four pairs of complexes shows that the frameworks can be tuned by various dicarboxylate coligands and changeable conformations of the hbmb ligand. In addition, the chemical stability, thermal stability and photoluminescent properties of complexes 1–8 have also been investigated.