Two-Dimensional Lanthanide Metal-Organic Frameworks as a Platform for Sensing Pollutant and Nitrophenols Reduction.

The discharge of harmful and toxic pollutants in water is destroying the ecosystem balance and human being health at an alarming rate. Therefore, the detection and removal of water pollutants by using stable and efficient materials are significant but challenging. Herein, three novel lanthanide metal-organic frameworks (Ln-MOFs), [La(L)(DMF)2(H2O)2]·H2O (LCUH-104), [Nd(L)(DMF)2(H2O)2]·H2O (LCUH-105), and [Pr(L)(DMF)2(H2O)2]·H2O (LCUH-106) [H3L = 5-(4-(tetrazol-5-yl)phenyl)isophthalic acid (H3TZI)] were solvothermally constructed and structurally characterized. In the three Ln-MOFs, dinuclear metallic clusters {Ln2} were connected by deprotonated tetrazol-containing dicarboxylate TZI3- to obtain a 2D layered framework with a point symbol of {42·84}·{46}. Their excellent chemical and thermal stabilities were beneficial to carry out fluorescence sensing and achieve the catalytic nitrophenols (NPs) reduction. Especially, the incorporation of the nitrogen-rich tetrazole ring into their 2D layered frameworks enables the fabrication of Pd nanocatalysts (Pd NPs@LCUH-104/105/106) and have dramatically enhanced catalytic activity by using the unique metal-support interactions between three Ln-MOFs and the encapsulating palladium nanoparticles (Pd NPs). Specifically, the reduction of NPs (2-NP, 3-NP, and 4-NP) in aqueous solution by Pd NPs@LCUH-104 exhibits exceptional conversion efficiency, remarkable rate constants (k), and outstanding cycling stability. The catalytic rate of Pd NPs@LCUH-104 for 4-NP is nearly 8.5 times more than that of Pd/C (wt 5%) and its turnover frequency value is 0.051 s-1, which indicate its excellent catalytic activity. Meanwhile, LCUH-105, as a multifunctional fluorescence sensor, exhibited excellent fluorescence detection of norfloxacin (NFX) (turn on) and Cr2O72- (turn off) with high selectivity and sensitivity at a low concentration, and the corresponding fluorescence enhancement/quenching mechanism has also been systematically investigated through various detection means and theoretical calculations.

A Multifunctional Co-Based Metal-Organic Framework as a Platform for Proton Conduction and Ni trophenols Reduction.

The design and development of proton conduction materials for clean energy-related applications is obviously important and highly desired but challenging. An ultrastable cobalt-based metal-organic framework Co-MOF, formulated as [Co2(btzip)2(µ2-OH2)] (namely, LCUH-103, H2btzip = 4, 6-bis(triazol-1-yl)-isophthalic acid) had been successfully synthesized via the hydrothermal method. LCUH-103 exhibits a three-dimensional framework and a one-dimensional microporous channel structure with scu topology based on the binuclear metallic cluster {Co2}. LCUH-103 indicated excellent chemical and thermal stability; peculiarly, it can retain its entire framework in acid and alkali solutions with different pH values for 24 h. The excellent stability is a prerequisite for studying its proton conductivity, and its proton conductivity σ can reach up to 1.25 × 10-3 S·cm-1 at 80 °C and 100% relative humidity (RH). In order to enhance its proton conductivity, the proton-conducting material Im@LCUH-103 had been prepared by encapsulating imidazole molecules into the channels of LCUH-103. Im@LCUH-103 indicated an excellent proton conductivity of 3.18 × 10-2 S·cm-1 at 80 °C and 100% RH, which is 1 order of magnitude higher than that of original LCUH-103. The proton conduction mechanism was systematically studied by various detection means and theoretical calculations. Meanwhile, LCUH-103 is also an excellent carrier for palladium nanoparticles (Pd NPs) via a wetness impregnation strategy, and the nitrophenols (4/3/2-NP) reduction in aqueous solution by Pd@LCUH-103 indicated an outstanding conversion efficiency, high rate constant (k), and exceptional cycling stability. Specifically, the k value of 4-NP reduction by Pd@LCUH-103 is superior to many other reported catalysts, and its k value is as high as 1.34 min-1 and the cycling stability can reach up to 6 cycles. Notably, its turnover frequency (TOF) value is nearly 196.88 times more than that of Pd/C (wt 5%) in the reaction, indicating its excellent stability and catalytic activity.

Series of Dual Functional Two-Dimensional RE-OFs for Nitrophenol Reduction and Dye Separation.

The rational design and preparation of stable and multifunctional metal-organic frameworks (MOFs) with excellent catalysis and adsorption properties are desirable but are great challenges. The nitrophenol (NP) reduction to aminophenols (APs) by using the catalyst Pd@MOFs is an effective strategy, which has attracted extensive attention in recent years. Here, we report four stable isostructural two-dimensional (2D) rare earth metal-organic frameworks [RE4(AAPA)6(DMA)2 (H2O)4][DMA]3[H2O]8 (namely LCUH-101, RE = Eu, Gd, Tb, Y; AAPA2- = 5-[(anthracen-9-yl-methyl)-amino]-1,3-isophthalate), which feature a 2D layer structure with sql topology of point symbol {44·62} and exhibit excellent chemical stability and thermostability. The as-synthesized Pd@LCUH-101 was utilized for the catalytic reduction of 2/3/4-nitrophenol, which indicates high catalytic activity and recyclability attributed to the synergistic effect between Pd nanoparticles and the 2D layered structure. Of note, the turnover frequency (TOF), the reaction rate constant (k), and the activation energy (Ea) of Pd@LCUH-101 (Eu) in the reduction of 4-NP, respectively, are 1.09 s-1, 2.17 min-1, and 50.2 kJ·mol-1, which show that it has superior catalytic activity. Remarkably, LCUH-101 (Eu, Gd, Tb, and Y) are multifunctional MOFs that can effectively absorb and separate mixed dyes. The appropriate interlayer spacing enables them to efficiently adsorb methylene blue (MB) and rhodamine B (RhB) in aqueous solution, with adsorption capacities of 0.97 and 0.41 g·g-1, respectively, which is one of the highest values among those of the reported MOF-based adsorbers. Meanwhile, LCUH-101 (Eu) can be used for the separation of the dye mixture MB/MO and RhB/MO, and the excellent reusability enables LCUH-101 (Eu) to be used as chromatographic column filters to quickly separate and recover dyes. Therefore, this work provides a new strategy for the exploitation of stable and efficient catalysts for NP reduction and adsorbents for dyes.

Series of Stable Anionic Lanthanide Metal-Organic Frameworks as a Platform for Pollutant Separation and Efficient Nanoparticle Catalysis.

Eight new stable porous lanthanide metal-organic frameworks (Ln-OFs), namely, [Ln2(BPTC)2][(CH3)2NH2]2 [Ln = Ho (1), Eu (2), Gd (3), Dy (4), Er (5), Tm (6), Yb (7), Lu (8)], were prepared by 3,3',5,5'-biphenyltetracarboxylic acid (H4BPTC) and lanthanide ions by solvothermal reactions. Complexes 1-8 show a three-dimensional (3D) 6,6-connected network {412·63}·{48·66·8} topology based on binuclear (Ln2) clusters and feature a one-dimensional curving porous channel occupied by exchangeable dimethylamine cations ([(CH3)2NH2]+) in the 3D anionic frameworks. The occupied [(CH3)2NH2]+ in the anionic channels exhibited excellent ion-exchange ability, which is favorable to Pd2+ and cationic dye adsorption. Consequently, 1-8 were used to load Pd nanoparticles to catalyze the reduction of nitrophenols and adsorb and desorb methyl blue (MB). The catalytic reaction efficiencies of Pd@1-8 were higher than that of Pd/C (5 wt %) in the hydrogenation reaction of p-nitrophenol (p-NP). Moreover, Pd@1 exhibited good cycle stability and achieved nearly 100% p-NP conversion after eight cycles. Meanwhile, compound 1 also exhibited a high adsorption ability of MB, possessing an adsorption capacity of 1.41 g·g-1 (second only to 1.49 g·g-1 reported in the literature) selectively over rhodamine B (RhB) and methyl orange (MO) in aqueous solutions. Remarkably, the skeleton of 1 remained stable after four adsorption-desorption cycles of MB in aqueous solution.

Series of TM-OFs as a Platform for Efficient Catalysis and Multifunctional Luminescence Sensing.

Three novel porous transition-metal-organic frameworks (TM-OFs), formulated as [Co3(DCPN)2(µ2-OH2)4(H2O)4](DMF)2 (1), [Cd3(DCPN)2(µ2-OH2)4(H2O)4](DMF)2 (2), and [CdK(DCPN)(DMA)] (3), have been successfully prepared via solvothermal conditions based on a 5-(3',6'-dicarboxylic phenyl) nicotinic carboxylic acid (H3DCPN) ligand. 1 and 2 both have the same porous 3D network structure with the point symbol of {410·614·84}·{45·6}2 based on trinuclear ({Co3} or {Cd3}) clusters, indicating a one-dimensional porous channel, and possess excellent water and thermal stability; 3 also displays a porous 3D network structure with a 4-connected sra topology based on the heteronuclear metal cluster {CdK}. Complex 1 can be used to load Pd nanoparticles (Pd NPs) via a wetness impregnation strategy to obtain Pd@1. The reduction of nitrophenols (2-NP, 3-NP, 4-NP) by Pd@1 in aqueous solution shows outstanding conversion, excellent rate constants (k), and remarkable cycling stability due to the synergistic effect of complex 1 and Pd NPs. Luminescence sensing tests confirmed that 2 is a reliable multifunctional chemical sensor with high selectivity and sensitivity for low concentrations of Fe3+, Cr2O72-, CPFX, and NFX. Specifically, 2 shows a fluorescence enhancement behavior toward fluoroquinolone antibiotics (CPFX and NFX), which has not been reported previously in the literature. Moreover, the rational mechanism of fluorescence sensing was also systematically investigated by various detection means and theoretical calculations.

Synthesis and Visualization of Entangled 3D Covalent Organic Frameworks with High-Valency Stereoscopic Molecular Nodes for Gas Separation.

The structural diversity of three-dimensional (3D) covalent organic frameworks (COFs) are limited as there are only a few choices of building units with multiple symmetrically distributed connection sites. To date, 4 and 6-connected stereoscopic nodes with Td , D3h , D3d and C3 symmetries have been mostly reported, delivering limited 3D topologies. We propose an efficient approach to expand the 3D COF repertoire by introducing a high-valency quadrangular prism (D4h ) stereoscopic node with a connectivity of eight, based on which two isoreticular 3D imine-linked COFs can be created. Low-dose electron microscopy allows the direct visualization of their 2-fold interpenetrated bcu networks. These 3D COFs are endowed with unique pore architectures and strong molecular binding sites, and exhibit excellent performance in separating C2 H2 /CO2 and C2 H2 /CH4 gas pairs. The introduction of high-valency stereoscopic nodes would lead to an outburst of new topologies for 3D COFs.

Substoichiometric 3D Covalent Organic Frameworks Based on Hexagonal Linkers.

Covalent organic frameworks (COFs), a fast-growing field in crystalline porous materials, have achieved tremendous success in structure development and application exploration over the past decade. The vast majority of COFs reported to date are designed according to the basic concept of reticular chemistry, which is rooted in the idea that building blocks are fully connected within the frameworks. We demonstrate here that sub-stoichiometric construction of 2D/3D COFs can be accomplished by the condensation of a hexagonal linker with 4-connected building units. It is worth noting that the partially connected frameworks were successfully reticulated for 3D COFs for the first time, representing the highest BET surface area among imine-linked 3D COFs to data. The unreacted benzaldehydes in COF frameworks can enhance C2H2 and CO2 adsorption capacity and selectivities between C2H2/CH4 and C2H2/CO2 for sub-stoichiometric 2D COFs, while the reserved benzaldehydes control the interpenetrated architectures for the 3D case, achieving a rare non-interpenetrated pts topology for 3D COFs. This work not only paves a new avenue to build new COFs and endows residual function groups with further applications but also prompts redetermination of reticular frameworks in highly connected and symmetrical COFs.

Interfacial Mo-N-C Bond Endowed Hydrogen Evolution Reaction on MoSe2@N-Doped Carbon Hollow Nanoflowers.

Molybdenum diselenide (MoSe2) has been considered as promising electrocatalysts for catalyzing the hydrogen evolution reaction (HER) due to its narrow band gap and appropriate adsorption free energy. However, its catalytic performance is still impeded by inferior electrical conductivity and insufficient active sites, thus leading to unsatisfactory HER performance. Herein, MoSe2@N-doped carbon (NC) hollow nanoflowers with interfacial Mo-N-C bonds were controllably fabricated through the in situ selenization of the self-polymerized Mo-polydopamine precursor. Benefiting from the unique hollow structure, NC protective layer, and intimate interfacial interaction, the optimal MoSe2@NC displays good HER performance with low overpotentials (175 and 183 mV) and long-term stability (up to 12 h at -10 mA cm-2) in 0.5 M H2SO4 and 1.0 M KOH solutions, respectively. The theoretical results show that Mo-N-C bonds at the interface of MoSe2@NC give rise to relatively low unoccupied eg orbital density of states and ideal H2 adsorption free energy. This work presented here highlights the critical role of interfacial chemical bonds in regulating the electronic structure of nanomaterials and further improving the HER performance.

One-step Ethylene Purification from an Acetylene/Ethylene/Ethane Ternary Mixture by Cyclopentadiene Cobalt-Functionalized Metal-Organic Frameworks.

The separation of ethylene (C2 H4 ) from a mixture of ethane (C2 H6 ), ethylene (C2 H4 ), and acetylene (C2 H2 ) at normal temperature and pressure is a significant challenge. The sieving effect of pores is powerless due to the similar molecular size and kinetic diameter of these molecules. We report a new modification method based on a stable ftw topological Zr-MOF platform (MOF-525). Introduction of a cyclopentadiene cobalt functional group led to new ftw-type MOFs materials (UPC-612 and UPC-613), which increase the host-guest interaction and achieve efficient ethylene purification from the mixture of hydrocarbon gases. The high performance of UPC-612 and UPC-613 for C2 H2 /C2 H4 /C2 H6 separation has been verified by gas sorption isotherms, density functional theory (DFT), and experimentally determined breakthrough curves. This work provides a one-step separation of the ternary gas mixture and can further serve as a blueprint for the design and construction of function-oriented porous structures for such applications.

Optimizing Multivariate Metal-Organic Frameworks for Efficient C2H2/CO2 Separation.

Adsorptive separation of acetylene (C2H2) from carbon dioxide (CO2) promises a practical way to produce high-purity C2H2 required for industrial applications. However, challenges exist in the pore environment engineering of porous materials to recognize two molecules due to their similar molecular sizes and physical properties. Herein, we report a strategy to optimize pore environments of multivariate metal-organic frameworks (MOFs) for efficient C2H2/CO2 separation by tuning metal components, functionalized linkers, and terminal ligands. The optimized material UPC-200(Al)-F-BIM, constructed from Al3+ clusters, fluorine-functionalized organic linkers, and benzimidazole terminal ligands, demonstrated the highest separation efficiency (C2H2/CO2 uptake ratio of 2.6) and highest C2H2 productivity among UPC-200 systems. Experimental and computational studies revealed the contribution of small pore size and polar functional groups on the C2H2/CO2 selectivity and indicated the practical C2H2/CO2 separation of UPC-200(Al)-F-BIM.

Accurately Regulating the Electronic Structure of Nix Sey @NC Core-Shell Nanohybrids through Controllable Selenization of a Ni-MOF for pH-Universal Hydrogen Evolution Reaction.

N-doped carbon-encapsulated transition metal selenides (TMSs) have garnered increasing attention as promising electrocatalysts for hydrogen evolution reaction (HER). Accurately regulating the electronic structure of these nanohybrids to reveal the underlying mechanism for enhanced HER performances is still challenging and thus requires deep excavation. Herein, a series of pomegranate-like Nix Sey @NC core-shell nanohybrids (including Ni0.85 Se @ NC, NiSe2 @NC, and NiSe@NC) through controllable selenization of a Ni-MOF precursor is reported. The component of the nanohybrids can be fine-tuned by tailoring the selenization temperature and feed ratio, through which the electronic structure can be synchronously regulated. Among these nanohybrids, the Ni0.85 Se @ NC exhibits the optimum pH-universal HER performance with overpotentials of 131, 135, and 183 mV in 0.5 m H2 SO4 , 1.0 m KOH, and 1.0 m PBS, respectively, at 10 mA cm-2 , which are attributed to the increased partial density of state at the Fermi level and effective van der Waals interactions between Ni0.85 Se and NC matrix explained by density functional theory calculations.

Sequential Solid-State Transformations Involving Consecutive Rearrangements of Secondary Building Units in a Metal-Organic Framework.

Solid-state transformations in metal-organic framework (MOF) systems are important phenomena and have led to the creation of new MOF structures. Solid-state transformations from interpenetrated to non-interpenetrated networks involving rearrangement of secondary building units (SBUs) in a single-crystal-to-single-crystal (SCSC) fashion have not been explored to date. Herein, we report the sequential, thermally stimulated solid-state transformations in a barium-organic framework ( UPC-600 ). The two-fold interpenetrated framework of  UPC-600  is converted at 373 K to UPC-601 , a non-interpenetrated framework. This proceeds in a SCSC fashion and involves the rearrangement of two proximate rod-shaped SBUs in different nets to generate a new rod-shaped SBU. At 473 K, a continuous solid-state transformation involving a second rearrangement occurred,  UPC-601  converted to UPC-602  by the rearrangement of the 1D rod-shaped SBU to a 2D layer SBU. This is the first example of such a thermally-driven stepwise transformation involving simultaneous cleavage and regeneration of multiple bonds. This result will enable detailed studies of solid-state transformations, and encourages a deep understanding of the role of solid-state transformations in the synthesis of MOF materials.

Sequential Solid-State Transformations Involving Consecutive Rearrangements of Secondary Building Units in a Metal-Organic Framework (MOF).

Solid-state transformations in metal-organic frameworks (MOFs) are important and have led to the creation of new MOF structures. Solid-state transformations from interpenetrated to non-interpenetrated networks involving rearrangement of secondary building units (SBUs) in a single-crystal-to-single-crystal (SCSC) fashion have not been explored to date. Herein, we report the sequential, thermally stimulated solid-state transformations in a barium-organic framework (UPC-600). The two-fold interpenetrated framework of UPC-600 is converted at 373 K into UPC-601, a non-interpenetrated framework. This proceeds in a SCSC fashion and involves the rearrangement of two proximate rod-shaped SBUs in different nets to generate a new rod-shaped SBU. At 473 K, a continuous solid-state transformation involving a second rearrangement occurred, UPC-601 converted into UPC-602 by the rearrangement of the 1D rod-shaped SBU to a 2D layer SBU. This is the first example of such a thermally driven stepwise transformation involving simultaneous cleavage and regeneration of multiple bonds.

Topology Exploration in Highly Connected Rare-Earth Metal-Organic Frameworks via Continuous Hindrance Control.

The structural diversity of highly connected metal-organic frameworks (MOFs) has long been limited due to the scarcity of highly connected metal clusters and the corresponding available topology. Herein, we deliberately chose a series of tritopic linkers with multiple substituents to construct a series of highly connected rare-earth (RE) MOFs. The steric hindrance of these substituents can be systematically tuned to generate various linker rotamers with tunable configurations and symmetries. For example, the methyl-functionalized linker (L-CH3) with C2 v symmetry exhibits larger steric hindrance, forcing two peripheral phenyl rings perpendicular to the central one. The combination of C2 v linkers and 9-connected RE6 clusters leads to the formation of a new fascinating (3,9)-c sep topology. Unlike Zr-MOFs exhibiting Zr6 clusters in various linker configurations and corresponding different structures, the adaptable RE6 clusters can undergo metal insertion and rearrange into new RE9 clusters when connected to an unfunctionalized linker (L-H) with C1 symmetry, giving rise to a new (3,3,18)-c ytw topology. More interestingly, by judiciously combining the linkers with both small and bulky substituents through mixed-linker strategies, an RE9-based MOF with an engaging (3,3,12)-c flg topology could be obtained as a result of continuous steric hindrance control. In this case, the two mixed linkers adopt configurations with moderate steric hindrances. Molecular simulation demonstrates that the combination of substituents with various steric hindrances dictates the resulting MOF structures. This work provides insights into the discovery of unprecedented topologies through systematic and continuous steric tuning, which can further serve as a blueprint for the design and construction of highly complicated porous structures for sophisticated applications.

Molecular Pivot-Hinge Installation to Evolve Topology in Rare-Earth Metal-Organic Frameworks.

Linker desymmetrization has been witnessed as a powerful design strategy for the discovery of highly connected metal-organic frameworks (MOFs) with unprecedented topologies. Herein, we introduce molecular pivot-hinge installation as a linker desymmetrization strategy to evolve the topology of highly connected rare-earth (RE) MOFs, where a pivot group is placed in the center of a linker similar to a hinge. By tuning the composition of pivot groups and steric hindrances of the substituents on various linker rotamers, MOFs with various topologies can be obtained. The combination of L-SO2 with C2v symmetry and 12-connected RE9 clusters leads to the formation of a fascinating (4,12)-c dfs new topology. Interestingly, when replacing L-SO2 with a tetrahedra linker L-O, the stacking behaviors of RE-organic layers switch from an eclipsed mode to a staggered stacking mode, leading to the discovery of an intriguing hjz topology. Additionally, the combination of the RE cluster and a linker [(L-(CH3 )6 )] with more bulky groups gives rise to a flu topology with a new 8-c inorganic cluster. The diversity of these RE-MOFs was further enhanced through post-synthetic installation of linkers with various functional groups. Functionalization of each linker with acidic and basic units in the mesoporous RE-based PCN-905-SO2 allows for efficient cascade catalytic transformation within the functionalized channels.

An Amino-Functionalized Metal-Organic Framework, Based on a Rare Ba12 (COO)18 (NO3 )2 Cluster, for Efficient C3 /C2 /C1 Separation and Preferential Catalytic Performance.

A barium(II) metal-organic framework (MOF) based on a predesigned amino-functionalized ligand, namely [Ba2 (L)(DMF)(H2 O)(NO3 )1/3 ]⋅DMF⋅EtOH⋅2 H2 O (UPC-33) [H3 L=4,4'-((2-amino-5-carboxy-1,3-phenylene)bis(ethyne-2,1-diyl))dibenzoic acid] has been synthesized. UPC-33 is a 3-dimensional 3,18-connected network with fcu topology with a rare twelve-nuclear Ba12 (COO)18 (NO3 )2 cluster. UPC-33 shows permanent porosity and a high adsorption heat of CO2 (49.92 kJ mol-1 ), which can be used as a platform for selective adsorption of CO2 /CH4 (8.09). In addition, UPC-33 exhibits high separation selectivity for C3 light hydrocarbons with respect to CH4 (228.34, 151.40 for C3 H6 /CH4 , C3 H8 /CH4 at 273k and 1 bar), as shown by single component gas sorption and selectivity calculations. Due to the existence of -NH2 groups in the channels, UPC-33 can effectively catalyze Knoevenagel condensation reactions with high yield, and substrate size and electron dependency.

A Stable Amino-Functionalized Interpenetrated Metal-Organic Framework Exhibiting Gas Selectivity and Pore-Size-Dependent Catalytic Performance.

An amino-functionalized doubly interpenetrated microporous zinc metal-organic framework (UPC-30) has been solvothermally synthesized. UPC-30 can be stable at 190 °C and confirmed by powder X-ray diffraction. Gas adsorption measurements indicate that UPC-30 exhibits high H2 adsorption heat and CO2/CH4 separation efficiency. After the exchange of Me2NH2+ by Li+ in the channels, the H2 adsorption heat increased by 19.7%. Because of the existence of -NH2 groups in the channels, UPC-30 can effectively catalyze Knoevenagel condensation reactions with high yield and pore-size-dependent selectivity.

Expanded Porous Metal-Organic Frameworks by SCSC: Organic Building Units Modifying and Enhanced Gas-Adsorption Properties.

Two amino-functional copper metal-organic frameworks of formula [Cu3(ATTCA)2(H2O)3]·2DMF·11H2O·12EtOH (1) (H3ATTCA = 2-amino-[1,1:3,1-terphenyl]-4,4,5-tricarboxylic acid, pyz = pyrazine, DMF = dimethylformamide) and [Cu3(ATTCA)2(pyz)(H2O)]·2DMF·12H2O·8EtOH (2) were synthesized under solvothermal conditions and characterized by single-crystal X-ray diffraction, infrared spectroscopy, elemental analyses, thermogravimetric analyses, and powder X-ray diffraction. Single-crystal X-ray diffraction analysis revealed that both complexes 1 and 2 are built of the Cu2(COO)4 paddlewheel secondary building units with an fmj topology. Importantly, complex 1 can be transformed into complex 2 by the single-crystal to single-crystal transformation of which the coordinated water molecules are replaced with pyz molecules. However, the adsorption abilities of 2 are obviously lower than those of 1, as its pores are partially blocked by pyz molecules. Moreover, gas-adsorption analysis showed that the amino-functional 1 possesses higher gas-adsorption capacity than UMCM-151 for N2, H2, CH4, and C2H2, especially for CO2.

Unprecedented Solvent-Dependent Sensitivities in Highly Efficient Detection of Metal Ions and Nitroaromatic Compounds by a Fluorescent Barium Metal-Organic Framework.

The assembly of a fluorescent dicarboxylate ligand with a barium ion resulted in the formation of a 3D metal-organic framework, Ba5(ADDA)5(EtOH)2(H2O)3·5DMF (UPC-17), based on a 1D rod-shaped secondary building unit. The unprecedented solvent-dependent sensitivities of UPC-17 for the detection of Fe(3+)/Al(3+) ions and 4-nitrophenol with high efficiency were observed for the first time. Significantly, UPC-17 exhibits superior "turn-off" detection for the Fe(3+) ion in methanol and acetone emulsions but shows "turn-on" detection in tetrahydrofuran emulsion. Furthermore, the visible color changes in the detection process make them easy to distinguish by the naked eye, which further increases its application potential.

Tuning the Dimensionality of Interpenetration in a Pair of Framework-Catenation Isomers To Achieve Selective Adsorption of CO2 and Fluorescent Sensing of Metal Ions.

A pair of framework-catenation isomers (UPC-19 and UPC-20) based on an anthracene-functionality dicarboxylate ligand were synthesized and characterized for the first time through tuning of the dimensionality of interpenetration. The interpenetration dimensionality significantly influences the properties including the porosity, gas-uptake capacity, and fluorescent sensing ability: UPC-19 with 5-fold interpenetration is nonporous, whereas the 3-fold interpenetration form of UPC-20 is porous and exhibits selective adsorption of CO2 and fluorescent sensing of Cu(2+) and Fe(3+) through fluorescence quenching.