A Series of 2D and 3D Metal-Organic Frameworks Based on a Flexible Tetrakis(4-pyridyloxymethylene)methane Ligand and Polycarboxylates: Syntheses, Structures, and Photoluminescent Properties

A series of structurally diverse metal-organic frameworks (MOFs), [Co-4(TPOM)(2)(L1)(4)(H2O)(4)]center dot H2O (1), [Ni-2(TPOM)(L2)(2)-(H2O)(2)]center dot 2H(2)O (2), [Co-2(TPOM)(L2)(2)(H2O)(2)]center dot H2O (3), [Cu-4(TPOM)(2)-(L3)(4)]center dot 3H(2)O (4), [Co-2(TPOM)(0.5)(L4)] (5), and [Cd(TPOM)(L3)(3)]center dot 7H(2)O (6), where TPOM = tetrakis(4-pyridyloxymethylene)methane, H(2)L1 = 1,3-benzenedicarboxylic acid, H(2)L2 = 5-hydroxyisophthalic acid, H(3)L3 = 1,3,5-benzenetricarboxylic acid, and H(4)L4 = 1,2,4,5-benzenetetracarboxylic acid, have been hydrothermally synthesized. These complexes were structurally characterized by X-ray diffraction analyses and further characterized by infrared spectra (IR), elemental analyses, powder X-ray diffraction (PXRD), and thermogravimetric (TG) analyses. Compound 1 shows a 3D 4-connected framework with a rare (8(4).6(2)) topology. Compounds 2 and 3 are isostructural and display 3D 2-fold interpenetrating frameworks with (6(4).8(2))(6(6))(2) topologies. Compound 4 exhibits a 2-fold interpenetrating structure with a scarce trinodal (3,4,5)-connected (4.6(2))(4.6(9))6(6) topology. Compound 5 possesses a 3D 4-connected net with the TPOM ligands located in the 3D channels. Compound 6 features 2D square layers (sql). The free TPOM ligands and L3 anions form discrete fragments through hydrogen bonds and pi-pi interactions. Interestingly, the fragments penetrate the 2D networks above and below to yield a unique 2D -> 3D polythreading framework. The structural differences among such compounds show the effects of the carboxylates and central metals on the complex structures. The UV-vis absorption spectra, optical energy gap, and luminescent properties were also investigated for the compounds.