Two new CdII MOFs of 1,4-bis(1H-benzimidazol-1-yl)butane and flexible dicarboxylate ligands: luminescence sensing towards Fe3+

Two new Cd-II MOFs, namely, two-dimensional (2D) poly[[[mu(2)-1,4-bis(1H-benzimidazol-1-yl)butane](mu(2)-heptanedioato)cadmium(II)] tetrahydrate], {[Cd(C7H10O4)(C18H18N4)]center dot 4H2O}(n) or {[Cd(Pim)(bbimb)]center dot 4H(2)O}(n) (1), and 2D poly[diaqua[mu(2)-1,4-bis(1H-benzimidazol-1-yl)butane](mu(4)-decanedioato)(mu(2)-decanedioato)dicadmium(II)], [Cd-2(C10H16O4)(2)(C18H18N4)(H2O)(2)](n) or [Cd(Seb)(bbimb)(0.5)(H2O)](n) (2), have been synthesized hydrothermally based on the 1,4-bis(1H-benzimidazol-1-yl)butane (bbimb) and pimelate (Pim(2-), heptanedioate) or sebacate (Seb(2-), decanedioate) ligands. Both MOFs were structurally characterized by single-crystal X-ray diffraction. In 1, the Cd-II centres are connected by bbimb and Pim(2-) ligands to generate a 2D sql layer structure with an octameric (H2O)(8) water cluster. The 2D layers are further connected by O-H center dot center dot center dot O hydrogen bonds, resulting in a three-dimensional (3D) supramolecular structure. In 2, the Cd-II centres are coordinated by Seb(2-) ligands to form binuclear Cd-2 units which are linked by bbimb and Seb(2-) ligands into a 2D hxl layer. The 2D layers are further connected by O-H center dot center dot center dot O hydrogen bonds, leading to an 8-connected 3D hex supramolecular network. IR and UV-Vis spectroscopy, thermogravimetric analysis and solid-state photoluminescence analysis were carried out on both MOFs. Luminescence sensing experiments reveal that both MOFs have good selective sensing towards Fe3+ in aqueous solution.