Two new Cd MOFs of 1,4-bis(1H-benzimidazol-1-yl)butane and flexible dicarboxylate ligands: luminescence sensing towards Fe.

Two new Cd MOFs, namely, two-dimensional (2D) poly[[μ-1,4-bis(1H-benzimidazol-1-yl)butanecadmium(II)] tetrahydrate], {[Cd(CHO)(CHN)]·4HO} or {[Cd(Pim)(bbimb)]·4HO} (1), and 2D poly[diaquaμ-1,4-bis(1H-benzimidazol-1-yl)butane(μ-decanedioato)dicadmium(II)], [Cd(CHO)(CHN)(HO)] or [Cd(Seb)(bbimb)(HO)] (2), have been synthesized hydrothermally based on the 1,4-bis(1H-benzimidazol-1-yl)butane (bbimb) and pimelate (Pim, heptanedioate) or sebacate (Seb, decanedioate) ligands. Both MOFs were structurally characterized by single-crystal X-ray diffraction. In 1, the Cd centres are connected by bbimb and Pim ligands to generate a 2D sql layer structure with an octameric (HO) water cluster. The 2D layers are further connected by O-H...O hydrogen bonds, resulting in a three-dimensional (3D) supramolecular structure. In 2, the Cd centres are coordinated by Seb ligands to form binuclear Cd units which are linked by bbimb and Seb ligands into a 2D hxl layer. The 2D layers are further connected by O-H...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 Fe in aqueous solution.