Metal–organic frameworks (MOFs) display a wide range of luminescent behaviors resulting from the multifaceted nature of their structure. In this critical review we discuss the origins of MOF luminosity, which include the linker, the coordinated metal ions, antenna effects, excimer and exciplex formation, and guest molecules. The literature describing these effects is comprehensively surveyed, including a categorization of each report according to the type of luminescence observed. Finally, we discuss potential applications of luminescent MOFs. This review will be of interest to researchers and synthetic chemists attempting to design luminescent MOFs, and those engaged in the extension of MOFs to applications such as chemical, biological, and radiation detection, medical imaging, and electro-optical devices (141 references).

Luminescent Metal–Organic Frameworks

Among the recent developments in metal-organic frameworks (MOFs), porous layered coordination polymers (CPs) have garnered attention due to their modular nature and tunable structures. These factors enable a number of properties and applications, including gas and guest sorption, storage and separation of gases and small molecules, catalysis, luminescence, sensing, magnetism, and energy storage and conversion. Among MOFs, two-dimensional (2D) compounds are also known as 2D CPs or 2D MOFs. Since the discovery of graphene in 2004, 2D materials have also been widely studied. Several 2D MOFs are suitable for exfoliation as ultrathin nanosheets similar to graphene and other 2D materials, making these layered structures useful and unique for various technological applications. Furthermore, these layered structures have fascinating topological networks and entanglements. This review provides an overview of different aspects of 2D MOF layered architectures such as topology, interpenetration, structural transformations, properties, and applications.

Two-Dimensional Metal-Organic Framework Materials: Synthesis, Structures, Properties and Applications.

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 to...

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

Ten new coordination polymers constructed from two structurally related ligands, 1,1′-(1,5-pentanedidyl)bis(imidazole) (biim-5) and 2,2′-bis(1H-imidazolyl)ether (BIE), have been synthesized: [Co(L1)(biim-5)] (1), [Co(L2)(biim-5)]·H2O (2), [Co(L3)(biim-5)] (3), [Co(L4)(biim-5)]·4H2O (4), [Co(L5)0.5(biim-5)] (5), [Co2(L6)(BIE)2]·1.5H2O (6), [Zn2(L6)(BIE)2]·2.5H2O (7), [Cd(L6)0.5(BIE)(H2O)]·H2O (8), [Zn2(L7)(BIE)2]·H2O (9) and [Cd(L8)0.5(BIE)(H2O)] (10), where H2L1 = 1,2-benzenedicarboxylic acid, H2L2 = 1,3-benzenedicarboxylic acid, H2L3 = 5-OH-1,3-benzenedicarboxylic acid, H2L4 = DL-camphoric acid, H4L5 = 1,2,3,4-butanetetracarboxylic acid, H4L6 = 4,4′-oxidiphthalic acid, H4L7 = 4,4′-(hexafluoroisopropylidene)diphthalic acid, and H4L8 = 1,2,3,4-benzenetetracarboxylic acid. Compounds 1 and 4 display the same 2D layer structures with 63-hcb nets, but in 4 the water tetramers extend the layers to a 3D supramolecular framework by intermolecular hydrogen bonds. Compound 2 is an uncommon example of 2D double laye...

1D, 2D, and 3D Metal−Organic Frameworks Based on Bis(imidazole) Ligands and Polycarboxylates: Syntheses, Structures, and Photoluminescent Properties

Self-assembly of N,N,N′,N′-tetra(4-pyridyl)-1,4-phenylenediamine (L1) and N,N-di(2-pyridyl)-N′,N′-di(4-pyridyl)-1,4-phenylenediamine (L2) with MX2 (M = Zn, Cd, and Hg; X = Cl, Br, and I) generated novel supramolecular structures with a rich structural diversity. In the crystal of L1, all pyridyl rings are involved in intermolecular π···π stacking and T-shaped C−H···π interactions to form a two-dimensional (2D) network. [CdL1Cl2]n·nH2O (4), [CdL1I2]n (6), [HgL1Cl2]n (7), [HgL1Br2]n (8), [Cd4(L2)4Cl8]n·2nDMF (13), [CdL2Br2]n (14), [CdL2I2]n (15), and [HgL2Cl2]n·0.5nDMF (16) are coordination polymers. In complex 4, L1 utilizes all its pyridyl nitrogens to coordinate with Cd(II) centers to afford an unprecedented three-dimensional (3D) binodal (3,4)-connected network with the Schlafli symbol of (8.102)2(84.102). Complexes 6, 7, 8, 14, and 15 have zigzag or centipede-like 1D coordination structures. For complex 13, each Cd has an octahedral coordination environment, and the Cd centers are linked by dichloro-br...

Synthesis, Structures, and Photoluminescence of Zinc(II), Cadmium(II), and Mercury(II) Coordination Polymers Constructed from Two Novel Tetrapyridyl Ligands

A blue luminescent inorganic–organic hybrid with infinite [Cd3(μ3-OH)2(μ2-Cl)2] connectivity

The two new metal-organic coordination frameworks [Ni2(pydc)2(4,4′-bpy)(H2O)4]n·0.5n(4,4′-bpy)2H2O (1) and [Ni2(pydc)2(2,2′-bpy)2(H2O)2]n·2nH2O (2) (H2pydc = pyridine-3,4-dicarboxylic acid; bpy = bipyridine) have been synthesised under hydrothermal conditions and characterised by single-crystal X-ray diffraction analysis. The structure of 1 contains parallel rectangular channels that accommodate large 4,4′-bpy guests while that of 2 contains vertical channels coordinated to 2,2′-bpy ligands. Their magnetic analyses show that they exhibit different magnetic interactions. The red shifts of the peak in their emission spectra relative to those of the the free ligands could be attributable to the metal–ligand coordination. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Anjian Lan

Papers

A blue luminescent inorganic–organic hybrid with infinite [Cd3(μ3-OH)2(μ2-Cl)2] connectivity

Nickel-organic coordination layers with different directional cavities

Three-component reactions leading to 2D and 3D metal–organic frameworks assembled on dinickel-carboxylate secondary building units