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), [Co4(TPOM)2(L1)4(H2O)4]·H2O (1), [Ni2(TPOM)(L2)2(H2O)2]·2H2O (2), [Co2(TPOM)(L2)2(H2O)2]·H2O (3), [Cu4(TPOM)2(L3)4]·3H2O (4), [Co2(TPOM)0.5(L4)] (5), and [Cd(TPOM)(L3)3]·7H2O (6), where TPOM = tetrakis(4-pyridyloxymethylene)methane, H2L1 = 1,3-benzenedicarboxylic acid, H2L2 = 5-hydroxyisophthalic acid, H3L3 = 1,3,5-benzenetricarboxylic acid, and H4L4 = 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 (84·62) topology. Compounds 2 and 3 are isostructural and display 3D 2-fold interpenetrating frameworks with (64·82)(66)2 topologies. Compound 4 exhibits a 2-fold interpenetrating structure with a scarce trinodal (3,4,5)-connected (4·62)(4·69)66 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 π–π 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.