Pillared-layer Metal-organic Framework Research Articles

A pillar-layered metal-organic framework as luminescent sensor for selective and reversible response of chloroform

A new 3D metal-organic framework, namely, {Zn4(H2BPTC)2(HCOO)4}n (SNNU-1, H4BPTC=biphenyl-3,3',5,5'-tetracarboxylic acid, SNNU=Shaanxi Normal University) has been solvothermal synthesized. Four independent tetrahedral Zn atoms are connected by organic ligands to form a 2D Zn-H2BPTC layer, which is further bridged by in-situ generated HCOO- to give the 3D pillar-layered framework of SNNU-1. Unique Zn and H2BPTC all act as 4-connected nodes leading to a new 4,4,4-connected topological net with point symbol of {4·5·62·82}{4·52·62·8}{52·63·7}. Notably, intense blue emission band is observed for SNNU-1, which exhibits solvent-dependent effect. Compared to other common organic solvents, chloroform can specially improve the photoluminescent intensity of SNNU-1. Further repeated response and release experiments clearly showed that SNNU-1 can act as luminescent sensor for selective and reversible detection of chloroform.

A luminescent two-fold interpenetrated pillared-layer metal-organic framework for highly selective and sensitive sensing of Fe3 +

A luminescent three-dimensional metal-organic framework generally formulated as [Zn2(OH)(sip)(bpe)(H2O)]H2O (1), has been hydrothermally synthesized and characterized. It represents a new two-fold interpenetrated pillared-layer framework with (63)(69·8) topology constructed from π-electron-rich rigid ligand 5-sulfoisophthalic acid coupled with auxiliary ligand 1,2-bis(4-pyridyl)ethane. Interestingly, the strong emission of 1 could be quenched efficiently by trace amounts of Fe3+ at room temperature, even in the presence of other competing analogues, which indicated that 1 can serve as an excellent sensor for specific selective identification and quantification of Fe3+.

Positional isomerism-driven two 3D pillar-layered metal-organic frameworks: Syntheses, topological structures and photoluminescence properties

Two novel three-dimensional (3D) pillar-layered metal-organic frameworks (MOFs), namely [Zn2(μ2-OH)(boaba)(1,4-bmimb)]n (1) and {[Zn5K2(μ2-H2O)2(boaba)4(1,2-bmimb)2(H2O)2]·H2O}n (2), were prepared by hydrothermal reactions (H3boaba=3,5-bis-oxyacetate-benzoic acid; 1,4-bmimb=1,4-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene; 1,2-bmimb =1,2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene). Notably, 1 exhibits a (3,5)-connected binodal (63)(69·8)-gra net with binuclear [Zn2(μ2-OH)(COO)]2+ clusters, while 2 shows a novel (4,4,5,9)-connected 4-nodal net constructed from the unique Zn(II)-K(I) heterometal rod-like substructures. The results indicate that the disposition of the 2-methylimidazolyl groups of bis(imidazole) ligands have a significant effect on structural diversity. Moreover, the photoluminescence properties of 1 and 2 have been investigated.

Selective Sorption of Light Hydrocarbons on a Family of Metal-Organic Frameworks with Different Imidazolate Pillars.

Four isostructural pillared-layer metal-organic frameworks (as 1-ims series) are successfully synthesized via the charge-balance approach, where trigonal [Zn2(CO2)3] cluster-based cationic layers [Zn2(NH2-BTB)](+) (NH2-H3BTB = 1,3,5-(3-benzoic acid) aniline) are connected by a series of 2-substituted imidazolates. The 1-ims supply a systematic platform to explore the adsorption of light hydrocarbons. Especially, 1-ims shows good adsorption selectivity of C3/C1 and C2/C1, and the selectivities of C3H8/CH4 are all over 100 at room temperature. These results demonstrate that introduction of functional group plays a key role on tuning the channel and pore size as well as improving the adsorption selectivity.

The construction, structures, and functions of pillared layer metal–organic frameworks

Pillared layer metal–organic frameworks (PL-MOFs), belonging to one representative of porous materials, have witnessed major advances in the past few years.

Visible-light-induced controlled radical polymerization of methacrylates mediated by a pillared-layer metal–organic framework

A visible light responsive MOF material has been constructed by the pillared-layer approach to conduct atom transfer radical polymerization. The as-prepared polymers show narrow molecular weight distribution and high retention of chain-end activity.

Mixed-linker solid solutions of functionalized pillared-layer MOFs - adjusting structural flexibility, gas sorption, and thermal responsiveness.

Flexible metal-organic frameworks (MOFs) can undergo fascinating structural transitions triggered by external stimuli, such as adsorption/desorption of specific guest molecules or temperature changes. In this detailed study we investigate the potentials and limitations of tuning framework flexibility systematically by exploiting the powerful concept of mixed-linker solid solutions. We chose the prototypical family of functionalized pillared-layer MOFs of the general type Zn2(fu(1)-bdc)2x(fu(2)-bdc)(2-2x)dabco (with x = 1.00, 0.75, 0.50, 0.25 and 0.00; fu-bdc = 2,5-dialkoxy-1,4-benzenedicarboxylate with varying alkoxy chain length, dabco = 1,4-diazabicyclo[2.2.2]octane) and examined their guest responsive, as well as intrinsic temperature dependent structural flexibility by X-ray diffraction, gas physisorption and calorimetric measurements. The ratio of the different fu-bdc linkers can be adjusted freely, offering opportunity for a targeted design of these functional materials by modulating their key features, such as magnitude of framework contraction upon guest removal, breathing behaviour upon CO2 adsorption/desorption, thermoresponsive phase behaviour, and their general thermal expansivity, by the careful choice of fu-bdc linkers and their combination.

A pillared-layer framework with high uptake and selective sorption of light hydrocarbons.

A new pillared-layer metal-organic framework [Zn2(NH2-BTB)(2-nim)] () was successfully synthesized based on mixed ligands, where binuclear [Zn2(CO2)3](+) cluster-based cationic layers [Zn2(NH2-BTB)](+) (NH2-H3BTB = 1,3,5-(three-benzoic acid)aniline) are connected by 2-nitroimidazoles. Compound shows high uptake and good adsorption selectivities for C3/C1 and C2/C1. Particularly, the C2H2 uptake capacity of is up to 152 cm(3) g(-1) at 273 K and the selectivity for C3H8/CH4 is over 85 at room temperature.

A new Co-nitroimidazolate–dicarboxylate pillared-layer network with various types of channels and ultra-large cages for gas uptake

A 3-D pillared-layer metal–organic framework constructed from unprecedented Co3-Co2-bdc-based layers and 2-nitroimidazole as pillars exhibits various types of pores and a nanometer-sized cavity along with a high CO2 uptake capacity (73.3 cm3 g−1 at 273 K and 1 atm).

Influence of Co-adsorbates on CO2 induced phase transition in functionalized pillared-layered metal–organic frameworks

Co-adsorption measurements reveal the flexible and gas separation behavior of functionalized pillared-layered MOFs when exposed to gas mixtures.

Syntheses, structures and investigation of the properties of mercury coordination polymers based on 5-amino-tetrazolate ligands

Four new mercury coordination polymers were successfully synthesized under solvothermal conditions and characterized by elemental analysis, IR spectroscopy, thermal analysis, powder X-ray diffraction and single-crystal X-ray diffraction. In these complexes, the chemical valence of mercury is +2, except for complex 1 which is +1. 1 contains [Hg2]2+ metal–metal bonded cores which are bounded by atz− (Hatz = 5-amino-tetrazolate) ligands and features a two-dimensional (2D) uninodal 3-connected ‘hcb’ network. 2 exhibits a trinodal 3D (3,6)-connected ‘apo/alpha-PbO2’ topological net in which 2D [HgCl]nn+ inorganic cation layers are pillared by atz− ligands. In 3, the 2D [HgCl]nn+ cation layers are interconnected by atz− ligands, affording a trinodal 3D (3,6)-connected ‘flu/fluorite’ topological net. 4 is a 3D pillared-layer metal–organic framework based on mixed atz− and isonicotinic ligands, showing a binodal (4,6)-connected ‘fsc’ coordination network. In this work, 1 and 4 were synthesized from an in situ generated tetrazolate ligand, while 2 and 3 were prepared from a commercially available tetrazolate ligand. These results indicate that the final structures of the target complexes will highly depend on the synthetic conditions as well as the preparation methods. Moreover, the photoluminescence properties of these complexes were investigated. Impressively, the non-centrosymmetric complex 3 displays not only a second harmonic generation (SHG) response but also a ferroelectric behavior.

Design of Pore Size and Functionality in Pillar-Layered Zn-Triazolate-Dicarboxylate Frameworks and Their High CO2/CH4 and C2 Hydrocarbons/CH4 Selectivity.

In the design of new materials, those with rare and exceptional compositional and structural features are often highly valued and sought after. On the other hand, materials with common and more accessible modes can often provide richer and unsurpassed compositional and structural variety that makes them a more suitable platform for systematically probing the composition-structure-property correlation. We focus here on one such class of materials, pillar-layered metal-organic frameworks (MOFs), because different pore size and shape as well as functionality can be controlled and adjusted by using pillars with different geometrical and chemical features. Our approach takes advantage of the readily accessible layered Zn-1,2,4-triazolate motif and diverse dicarboxylate ligands with variable length and functional groups, to prepare seven Zn-triazolate-dicarboxylate pillar-layered MOFs. Six different gases (N2, H2, CO2, C2H2, C2H4, and CH4) were used to systematically examine the dependency of gas sorption properties on chemical and geometrical properties of those MOFs as well as their potential applications in gas storage and separation. All of these pillar-layered MOFs show not only remarkable CO2 uptake capacity, but also high CO2 over CH4 and C2 hydrocarbons over CH4 selectivity. An interesting observation is that the BDC ligand (BDC = benzenedicarboxylate) led to a material with the CO2 uptake outperforming all other metal-triazolate-dicarboxylate MOFs, even though most of them are decorated with amino groups, generally believed to be a key factor for high CO2 uptake. Overall, the data show that the exploration of the synergistic effect resulting from combined tuning of functional groups and pore size may be a promising strategy to develop materials with the optimum integration of geometrical and chemical factors for the highest possible gas adsorption capacity and separation performance.

Direct and post-synthesis incorporation of chiral metallosalen catalysts into metal-organic frameworks for asymmetric organic transformations.

Two chiral porous metal-organic frameworks (MOFs) were constructed from [VO(salen)]-derived dicarboxylate and dipyridine bridging ligands. After oxidation of V(IV) to V(V) , they were found to be highly effective, recyclable, and reusable heterogeneous catalysts for the asymmetric cyanosilylation of aldehydes with up to 95 % ee. Solvent-assisted linker exchange (SALE) treatment of the pillared-layer MOF with [Cr(salen)Cl]- or [Al(salen)Cl]-derived dipyridine ligands led to the formation of mixed-linker metallosalen-based frameworks and incorporation of [Cr(salen)] enabled its use as a heterogeneous catalyst in the asymmetric epoxide ring-opening reaction.

Formation of a Syndiotactic Organic Polymer Inside a MOF by a [2+2] Photo-Polymerization Reaction.

Getting suitable crystals for single-crystal X-ray crystallographic analysis still remains an art. Obtaining single crystals of metal-organic frameworks (MOFs) containing organic polymers poses even greater challenges. Here we demonstrate the formation of a syndiotactic organic polymer ligand inside a MOF by quantitative [2+2] photopolymerization reaction in a single-crystal-to-single-crystal manner. The spacer ligands with trans,trans,trans-conformation in the pillared-layer MOF with guest water molecules in the channels, undergo pedal motion to trans,cis,trans-conformation prior to [2+2] photo-cycloaddition reaction and yield single crystals of MOF containing two-dimensional coordination polymers fused with the organic polymer ligands. We also show that the organic polymer in the single crystals can be depolymerized reversibly by cleaving the cyclobutane rings upon heating. These MOFs also show interesting photoluminescent properties and sensing of small organic molecules.

Evidence of Amine-CO2 Interactions in Two Pillared-Layer MOFs Probed by X-ray Crystallography.

Two pillared-layer metal-organic frameworks (MOFs; PMOF-55 and NH2 -PMOF-55) based on 1,2,4-triazole and terephthalic acid (bdc)/NH2 -bdc ligands were assembled and display framework stabilities, to a certain degree, in both acid/alkaline solutions and toward water. They exhibit high CO2 uptakes and selective CO2 /N2 adsorption capacities, with CO2 /N2 selectivity in the range of 24-27, as calculated by the ideal adsorbed solution theory method. More remarkably, the site and interactions between the host network and the CO2 molecules were investigated by single-crystal X-ray diffraction, which showed that the main interaction between the CO2 molecules and PMOF-55 is due to multipoint supramolecular interactions of C-H⋅⋅⋅O, C⋅⋅⋅O, and O⋅⋅⋅O. Amino functional groups were shown to enhance the CO2 adsorption and identified as strong adsorption sites for CO2 by X-ray crystallography.

A three-dimensional pillared-layer metal-organic framework: Synthesis, structure and gas adsorption studies

A stable 3D MOF, {[Zn3(L)3(DPB)1.5]·6DMF·H2O}n was synthesized using a partially methylated linear rigid linker (LH2) in the presence of the co-linker DPB (1,4-dipyridylbenzene) under solvothermal condition. The complex was found to have channels along the crystallographic a-axis with the pore surfaces aligned with –CH3 groups that resulted in a hydrophobic environment inside the cavity. Thermogravimetric analysis and variable temperature powder X-ray diffraction show high thermal stability of the framework. The solvent molecules in the cavity can be evacuated maintaining the structural integrity of the framework to afford a porous structure. Gas (N2, CH4, CO2 and H2) adsorptions were carried out for this MOF. The desolvated framework shows significant CO2 adsorption over N2 and CH4 at 273K with an isosteric heat of adsorption of ∼21kJ/mol, suggesting a strong interaction of the CO2 molecules with the framework walls.

Isolation of a structural intermediate during switching of degree of interpenetration in a metal-organic framework.

A known pillared layered metal-organic framework [Co2(ndc)2(bpy)] is shown to undergo a change in degree of interpenetration from a highly porous doubly-interpenetrated framework (2fa) to a less porous triply-interpenetrated framework (3fa). The transformation involves an intermediate empty doubly-interpenetrated phase (2fa') which has been isolated for the first time for this kind of phenomenon by altering the conditions of activation of the as-synthesized material. Interestingly, all the transformations occur in single-crystal to single-crystal fashion. Changes in degree of interpenetration have not been explored much to date and their implications with regard to the porosity of MOFs still remain largely unknown. The present study not only provides a better understanding of such dramatic structural changes in MOF materials, but also describes an original way of controlling interpenetration by carefully optimizing the temperature of activation. In addition to studying the structural mechanism of conversion from 2fa to 3fa, sorption analysis has been carried out on both the intermediate (2fa') and the triply-interpenetrated (3fa) forms to further explain the effect that switching of interpenetration mode has on the porosity of the MOF material.

High and selective CO2 uptake in a nitrogen-rich pillar-layered metal organic framework

A pillar-layered cobalt(ii) MOF exhibits high CO2 uptake and CO2/N2 selectivity, fast adsorption kinetics, easy regeneration and excellent stability.

A stable luminescent anionic porous metal–organic framework for moderate adsorption of CO2 and selective detection of nitro explosives

A new stable pillared-layer metal–organic framework was constructed, which showed moderate adsorption of CO2 and selective sensing of TNP.

Tuning Two-Dimensional Layer to Three-Dimensional Pillar-Layered Metal–Organic Frameworks: Polycatenation and Interpenetration Behaviors

A two-dimensional honeycomb network of {[Zn2(bpydb)2(H2O)2](DMA)3(H2O)}n (1) was solvothermally synthesized and structurally characterized. By employing 4,4′-bipyridine (bpy) as a pillar, two additional three-dimensional (3D) metal–organic frameworks (MOFs) of {[Zn2(bpydb)2(bpy)(EtO-H)2](DMF)(EtOH)}n (2) and {[Zn(bpydb)(bpy)](DMA)(EtOH)6}n (3) (bpydbH2 = 4,4′-(4,4′-bipyridine-2,6-diyl) dibenzoic acid, DMA = N,N- dimethylacetamide, DMF = N,N-dimethylformamide) were obtained. MOF 2 displays a 3D pillar-bilayered network generated from polycatenation of the 2D bilayers. By carefully adjusting the reaction condition, MOF 3 was harvested, showing a 2-fold interpenetrated (3,5)-connected hms net. The phase purity, thermal stability, and luminescent properties of the three MOFs were studied. In addition, N2 and CO2 adsorption behaviors of the activated 3 were investigated.