No abstract

Five new flexible functionalized aluminum hydroxo terephthalates [Al(OH)(BDC-X)]·n(guests) (BDC = 1,4-benzene-dicarboxylate; X = -Cl, 1-Cl; -Br, 2-Br; -CH(3), 3-CH(3); -NO(2), 4-NO(2); -(OH)(2), 5-OH(2)) were synthesized under solvothermal conditions. The as synthesized (Al-MIL-53-X-AS) as well as the activated compounds were characterized by X-ray powder diffraction (XRPD), IR spectroscopy, thermogravimetric (TG), and elemental analysis. Activation, that is, removal of unreacted H(2)BDC-X molecules and/or occluded solvent molecules, followed by hydration in air at room temperature, led to the narrow pore (NP) form of the title compounds [Al(OH)(BDC-X)]·n(H(2)O) (Al-MIL-53-X). Thermogravimetric analysis (TGA) and temperature-dependent XRPD (TDXRPD) experiments performed on the NP-form of the compounds indicate high thermal stability in the range 325-500 °C. As verified by N(2), CO(2), or H(2)O sorption measurements, most of the thermally activated compounds exhibit significant microporosity. Similar to pristine Al-MIL-53, the present compounds retain their structural flexibility depending on the nature of guest molecules and temperature, as verified by cell parameter determination from XRPD data. The breathing behavior of the functionalized frameworks upon dehydration-rehydration, investigated by temperature and time-dependent XRPD measurements, differs significantly compared to parent Al-MIL-53.

A general synthetic strategy has been developed, which can be used for the preparation of all the known as well as five new functionalised UiO‐66‐X compounds [X = H, F, F2, Cl, Cl2, Br, Br2, I, CH3, (CH3)2, CF3, (CF3)2, NO2, NH2, OH, (OH)2, OCH3, (CO2H)2, SO3H, C6H4]. Starting from a reaction mixture of ZrOCl2·8H2O, H2BDC‐X (BDC: 1,4‐benzenedicarboxylate), formic acid and N,N‐dimethylacetamide (DMA) having a molar ratio of 1:1:100:104.44, all the UiO‐66‐X compounds, except UiO‐66‐CO2H, were obtained under solvothermal conditions (150 °C, 24 h). The phase purity of all the compounds was ascertained by X‐ray powder diffraction (XRPD) analysis, DRIFT spectroscopy and elemental analysis. Determination of lattice parameters from the XRPD patterns of the new thermally activated UiO‐66‐X {X = CF3 (1‐CF3), (CO2H)2 [2‐(CO2H)2], F2 (3‐F2), Cl2 (4‐Cl2), Br2 (5‐Br2)} compounds revealed their structural similarity with the unfunctionalised UiO‐66. Thermogravimetric analyses (TGA) indicate that the five new compounds are stable in the range 290–390 °C in air. Except for 3‐F2, the new compounds maintain their structural integrity in water, acetic acid and 1 M HCl, as verified by XRPD analysis of the samples recovered after suspending them in the respective liquids. As confirmed by N2 and CO2 sorption analyses, all of the new thermally activated compounds exhibit significant microporosity values (SLangmuir = 217–836 m2 g–1), which are lower than that of the parent UiO‐66. Comparative CO2 sorption studies reveal that the UiO‐66‐X compounds with X = NO2, NH2, OH, CH3 and (CH3)2 show enhanced CO2 uptake compared to that of the parent compound at 1 bar and 0 °C.

Two novel metal coordination polymers, [Zn5Cl4(BBTA)3].3 DMF (1), and [ZnCl(BBTA)(0.5)(DMA)] (2) {H2-BBTA = 1H,5H-benzo(1,2-d:4,5-d')bistriazole}, have been synthesized under solvothermal conditions using ZnCl2 and H2-BBTA in DMF (DMF = N,N'-dimethylformamide) or DMA (DMA = N,N'-dimethylacetamide). Moreover, a highly efficient microwave synthetic route has been developed for 1. The structures of both compounds have been determined by single crystal X-ray diffraction. Compound 1 represents the first example of a novel family of cubic microporous metal-organic frameworks (MFU-4; Metal-Organic Framework Ulm University-4), consisting of dianionic BBTA2- linkers and pentanuclear {Zn5Cl4}6+ secondary building units, whereas compound 2 forms a dense 2D layered framework. Phase purity of both compounds was confirmed by X-ray powder diffraction (XRPD), IR spectroscopy, and elemental analysis. TGA and variable temperature XRPD (VTXRPD) experiments carried out on 1 indicate that solvent molecules occluded in the large cavities of 1 can be removed at a temperature >250 degrees C in high vacuum without significant loss of crystallinity, giving rise to a metal-organic framework with void cavities. Due to the small diameter of the aperture joining the two types of cavities present in 1, the diffusion of guest molecules across the crystal lattice is largely restricted at ambient conditions. Compound 1 therefore exhibits a highly selective adsorption for hydrogen vs. nitrogen at -196 degrees C. The framework is stable against moisture and has a specific pore volume of 0.42 cm3 g(-1) estimated from the water adsorption isotherm.

aThree new functionalized UiO-66-X (X = -SO 3 H, 1; -CO 2 H, 2; -I; 3) frameworks incorporating BDC-X (BDC: 1,4-benzenedicarboxylate) linkers have been synthesized by a solvothermal method using conventional electric heating. The as-synthesized (AS) as well as the thermally activated compounds were characterized by X-ray powder diffraction (XRPD), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, thermogravimetric (TG), and elemental analysis. The occluded H 2 BDC-X molecules can be removed by exchange with polar solvent molecules followed by thermal treatment under vacuum leading to the empty-pore forms of the title compounds. Thermogravimetric analysis (TGA) and temperature-dependent XRPD (TDXRPD) experiments indicate that 1, 2 and 3 are stable up to 260, 340 and 360°C, respectively. The compounds maintain their structural integrity in water, acetic acid and 1 M HCl, as verified by XRPD analysis of the samples recovered after suspending them in the respective liquids. As confirmed by N 2 , CO 2 and CH 4 sorption analyses, all of the thermally activated compounds exhibit significant microporosity (S Langmuir : 769-842 m 2 g −1 ), which are comparable to that of the parent UiO-66 compound. Compared to the unfunctionalized UiO-66 compound, all the three functionalized solids possess higher ideal selectivity in adsorption of CO 2 over CH 4 at 33°C.

Para-disubstituted alkylaromatics such as p-xylene are preferentially adsorbed from an isomer mixture on three isostructural metal-organic frameworks: MIL-125(Ti) ([Ti(8)O(8)(OH)(4)(BDC)(6)]), MIL-125(Ti)-NH(2) ([Ti(8)O(8)(OH)(4)(BDC-NH(2))(6)]), and CAU-1(Al)-NH(2) ([Al(8)(OH)(4)(OCH(3))(8)(BDC-NH(2))(6)]) (BDC = 1,4-benzenedicarboxylate). Their unique structure contains octahedral cages, which can separate molecules on the basis of differences in packing and interaction with the pore walls, as well as smaller tetrahedral cages, which are capable of separating molecules by molecular sieving. These experimental data are in line with predictions by molecular simulations. Additional adsorption and microcalorimetric experiments provide insight in the complementary role of the two cage types in providing the para selectivity.

A vanadium based metal-organic framework (MOF), VO(BPDC) (BPDC(2-) = biphenyl-4,4'-dicarboxylate), adopting an expanded MIL-47 structure type, has been synthesized via solvothermal and microwave methods. Its structural and gas/vapor sorption properties have been studied. This compound displays a distinct breathing effect toward certain adsorptives at workable temperatures. The sorption isotherms of CO(2) and CH(4) indicate a different sorption behavior at specific temperatures. In situ synchrotron X-ray powder diffraction measurements and molecular simulations have been utilized to characterize the structural transition. The experimental measurements clearly suggest the existence of both narrow pore and large pore forms. A free energy profile along the pore angle was computationally determined for the empty host framework. Apart from a regular large pore and a regular narrow pore form, an overstretched narrow pore form has also been found. Additionally, a variety of spectroscopic techniques combined with N(2) adsorption/desorption isotherms measured at 77 K demonstrate that the existence of the mixed oxidation states V(III)/V(IV) in the titled MOF structure compared to pure V(IV) increases the difficulty in triggering the flexibility of the framework.

A new 3D fluorescent amide-functionalized Cd­(II)-based metal–organic framework (MOF) with molecular formula [Cd5Cl6(L)­(HL)2]·7H2O (1) was synthesized under solvothermal conditions using CdCl2·H2O and 4-(1H-tetrazol-5-yl)-N-[4-(1H-tetrazol-5-yl)­phenyl]­benzamide (H2 L) in DMF/methanol in the presence of conc. HCl. Single-crystal X-diffraction analysis reveals that the 3D framework structure of 1 is constructed from octahedrally coordinated Cd2+ ions interconncted by chloride anions and ditopic tetrazolate-based ligand molecules. The phase-purity of the compound was confirmed by X-ray powder diffraction (XRPD) analysis, infrared spectroscopy, and elemental analysis. Thermogravimetric analysis suggests that 1 is thermally stable up to 300 °C. Steady-state fluorescence titration experiments reveal that activated 1′ can selectively detect 2,4,6-trinitrophenol (TNP) in the presence of other competing nitroaromatic compounds with a detection limit of 42.84 ppb. Recyclability experiments reveal that 1′ retains its initial fluorescence intensity even after several cycles, suggesting high photostability and reusability for long-term sensing applications. The extraordinarily selective fluorescence quenching is assigned to the presence of energy and electron transfer processes as well as the electrostatic interactions of the MOF with TNP. This new 3D amide-functionalized MOF is a potential candidate that can be developed into a highly selective and sensitive sensing device for the in-field detection of TNP.