Metal-Organic Frameworks Based on Different Benzimidazole Derivatives: Effect of Length and Substituent Groups of the Ligands on the Structures

Seven coordination polymers constructed from Structurally related ligands, namely, [Cd-2(ODPT)(L1)(H2O)(2)]center dot H2O (1), [Cd-2(ODPT)(L2)(H2O)(2)] (2), [Zn-2(BPTC)(L3)]center dot(H2O)(3) (3), [Cd(m-BDC)(L4)] (4), [CdL5] (5), [CdL6]center dot H2O (6), and [ZnL6]center dot H2O (7) (H4ODPT = 4,4'-oxidiphthalic acid, H4BPTC = 3,3',4,4'-benzophenone tetracarboxylate ligand, H(2)m-BDC = 1,4-benzenedicarboxylate acid, L1 = 1,4-di(1H-benzo[d]imidazol-2-yl)butane, L2 = bis((1H-benzo[d]imidazol-2-yl)methyl)amine, L3 = 1,4-bis(1-(pyridin-4-ylmethyl)-1H-benzo[d]imidazol-2-yl)butane, L4 = bis((1-(pyridin-4-ylmethyl)-1H-benzo[d]imidazol-2-yl)methyl)amine, H(2)L5 = 4,4'-(2,2'-(butane-1,4-diyl)bis(1H-benzo[d](imidazole-2,1-diyl))bis(methylene)dibenzoic acid, and H(2)L6 = 2,2'-(2,2'-azanediylbis(methylene)bis(1H-benzo[(imidazole-2,1-diyl))diacetic acid) have been synthesized under hydrothermal conditions. Their structures have been determined by single crystal X-ray diffraction analyses and further characterized by elemental analyses, I R spectra, and thermogravimetric (TG) analyses. In 1, one kind of phthalate group of ODPT4- links Cd-II cations to form a Cd-O helical chain which is connected by L1 ligand and the other kind of phthalate group to form it two-dimensional (2D) layer. These layers are further connected by ether O atoms of ODPT4- anions to generate a three-dimensional (3D) network with (4(2).5(2).6(2))(4(2).5(2).6(4).7(2)) topology. Each ODPT4- anion links all Cd-II cations to form a 3D framework with (4(5).6(5))(4(7).6(8)) topological type, in which each L2 ligand coordinates to Cd-II with two imidazole nitrogen atoms and one imine nitrogen atom as a terminal ligand in 2. For 3, BPTC4- ligands link Zn1 and Zn2 cations to generate it right-handed helical chain. L3 ligands connect Zn cations from helical chains to extend to a 3D open framework, showing it (4(3).8(3))(2)(4(2).8(4))(4.8(5)) topology. L4 as terminal ligands coordinate to metal centers in it tridentate mode, and the m-BDC anion coordinates to metal to generate an infinite chain, which is linked by pi center dot center dot center dot pi interactions, giving a 2D supramolecular layer in 4. Each L5(2-) ligand shows a bis(monodentate) and bis(bidentate) coordination mode and connects four Cd-II cations to generate it PtS topological net in 5. Compounds 6 and 7 are isostructural and show 3D supramolecular nets constructed through pi center dot center dot center dot pi interactions between adjacent layers formed by L6(2-) and metal centers. By careful inspection of the structures of 1-7, we believe that the different lengths and substituent groups of N-donor ligands adopting various coordination modes are crucial factors for the formation of the different structures. The photoluminescent properties of L1-H(2)L6 and 1-7 have been studied in the solid state at room temperature.