Xi-Yan Dong

Highly selective Fe3+ sensing and proton conduction in a water-stable sulfonate–carboxylate Tb–organic-framework

A new 3D porous terbium–organic framework {[Tb4(OH)4(DSOA)2(H2O)8]·(H2O)8}n (Tb-DSOA) has been successfully assembled by Tb3+ ions and a sulfonate–carboxylate linker disodium-2,2′-disulfonate-4,4′-oxydibenzoic acid (Na2H2DSOA). In this metal–organic framework (MOF), tetranuclear terbium clusters can be sensitized by the organic linker to generate the characteristic photoluminescence of TbIII ions. Noncoordinated sulfonate oxygen atoms functionalize its channels, which act as basic sites leading to highly selective Fe3+ ion sensing by luminescence quenching, and also act as hopping sites for proton transfer, resulting in a proton conductivity of 1.66 × 10−4 S cm−1 at 98% RH. Exceptional water-stability makes this MOF compatible for these applications in aqueous solution.

Hypersensitive dual-function luminescence switching of a silver-chalcogenolate cluster-based metal–organic framework

Silver(i) chalcogenide/chalcogenolate clusters are promising photofunctional materials for sensing, optoelectronics and solar energy harvesting applications. However, their instability and poor room-temperature luminescent quantum yields have hampered more extensive study. Here, we graft such clusters to adaptable bridging ligands, enabling their interconnection and the formation of rigid metal-organic frameworks. By controlling the spatial separation and orientation of the clusters, they then exhibit enhanced stability (over one year) and quantum yield (12.1%). Ultrafast dual-function fluorescence switching (<1 s) is also achieved, with turn-off triggered by O2 and multicoloured turn-on by volatile organic compounds. Single-crystal X-ray diffraction of the inclusion materials, obtained by single-crystal-to-single-crystal transformation, enables precise determination of the position of the small molecules within the framework, elucidating the switching mechanism. The work enriches the cluster-based metal-organic framework portfolio, bridges the gap between silver chalcogenide/chalcogenolate clusters and metal-organic frameworks, and provides a foundation for further development of functional silver-cluster-based materials.

Ferroelectric switchable behavior through fast reversible de/adsorption of water spirals in a chiral 3D metal-organic framework.

A polar homochiral 3D MOF [{Co2(L)(bpe)(H2O)}·5H2O]n constructed with cobalt(II) and a new ligand N-(1,3-dicarboxy-5-benzyl)-carboxymethylglycine (H4L) accommodates ordered helical water streams in its helical grooves. It provides the first example of switchable ferroelectric and optical behavior through two-step reversible single-crystal to single-crystal transformation (SCSC) upon desorption/adsorption of water spirals and coordinated water molecules, respectively.

Aqueous- and vapor-phase detection of nitroaromatic explosives by a water-stable fluorescent microporous MOF directed by an ionic liquid

A water-stable fluorescent microporous metal–organic framework (MOF), [Tb(L)(OH)]·x(solv) (1), has been designed and successfully synthesized under a combination of hydro/solvothermal and ionothermal conditions (H2L = 5-(4-carboxyphenyl)pyridine-2-carboxylate). The crystal structure reveals that complex 1 consists of cubane-shaped tetranuclear terbium building units, which are further bridged by the multicarboxylate ligands to give a (3,12)-connected topology with the point symbol (420·628·818)(43)4. More importantly, the excellent hydrolytic stability allows it to be used in an aquatic system, which is highly desirable for practical applications. Activated 1 shows high selectivity and sensitivity towards nitroaromatic explosives in both aqueous and vapor phases. The sizes of the pore windows (11.2 × 11.2 A2) in 1, which are larger than the sizes of the selected nitroaromatics, could permit easy diffusion of analytes inside the channel, keeping the electron rich framework and electron deficient analytes in close proximity.

A tetranuclear Cu4(μ3-OH)2-based metal–organic framework (MOF) with sulfonate–carboxylate ligands for proton conduction

A new tetranuclear Cu4(μ3-OH)2-based metal-organic framework (MOF) with sulfonate-carboxylate ligands features large hydrophilic channels. This MOF exhibits proton conductivity over 10(-3) S cm(-1) at 85-100 °C and 98% relative humidity and colossal dielectric constant.

Unique Proton Dynamics in an Efficient MOF-Based Proton Conductor

Recently, research on metal-organic frameworks (MOFs) serving as a new type of proton conductive material has resulted in many exciting achievements. However, direct observation of a well-established proton-transfer mechanism still remains challenging in MOFs and other crystalline compounds, let alone other conductive materials. Herein we report the solvothermal synthesis of a new proton-conducting MOF, (Me2NH2)[Eu(L)] (H4L = 5-(phosphonomethyl)isophthalic acid). The compound consists of a layered anionic framework [Eu(L)]- and interlayer-embedded counter cations (Me2NH2)+, which interact with adjacent uncoordinated O atoms of phosphonate groups to form strongly (N-H···O) hydrogen-bonded chains aligned parallel to the c-axis. Facile proton transfer along these chains endows the compound with single-crystal anhydrous conductivity of 1.25 × 10-3 S·cm-1 at 150 °C, and water-assisted proton conductivity for a compacted pellet of microcrystalline crystals attains 3.76 × 10-3 S·cm-1 at 100 °C and 98% relative humidity (RH). Proton dynamics (vibrating and transfer) within N-H···O chains of the compound are directly observed using a combination of anisotropic conductivity measurements and control experiments using large single-crystals and pelletized samples, in situ variable-temperature characterization techniques including powder X-ray diffraction (PXRD), single-crystal X-ray diffraction (SCXRD), diffuse reflectance infrared Fourier transform spectrum (DRIFTS), and variable-temperature photoluminescence. In particular, a scarce single-crystal to single-crystal (SCSC) transformation accompanied by proton transfer between an anionic structure (Me2NH2)[Eu(L)] and an identical neutral framework [Eu(HL)] has been identified.

A Crystalline Copper(II) Coordination Polymer for the Efficient Visible-Light-Driven Generation of Hydrogen

A crystalline coordination polymer (CP) photocatalyst (Cu-RSH) which combines redox-active copper centers with photoactive rhodamine-derived ligands remains stable in acid and basic solutions from pH 2 to 14, and efficiently catalyzes dihydrogen evolution at a maximum rate of 7.88 mmol g(-1)  h(-1) in the absence of a mediator and a co-catalyst. Cyclic voltammetry, control experiments, and DFT calculations established that copper nodes with open coordination sites and favorable redox potentials, aided by spatially ordered stacking of rhodamine-based linkers, account for the high catalytic performance of Cu-RSH. Emission quenching, time-resolved fluorescence decay, and transient photocurrent experiments disclosed the charge separation and transfer process in the catalytic system. The present study demonstrates the potential of crystalline copper CPs for the practical utilization of light.

MOF‐Derived Bifunctional Cu3P Nanoparticles Coated by a N,P‐Codoped Carbon Shell for Hydrogen Evolution and Oxygen Reduction

Metal-organic frameworks (MOFs) have recently emerged as a type of uniformly and periodically atom-distributed precursor and efficient self-sacrificial template to fabricate hierarchical porous-carbon-related nanostructured functional materials. For the first time, a Cu-based MOF, i.e., Cu-NPMOF is used, whose linkers contain nitrogen and phosphorus heteroatoms, as a single precursor and template to prepare novel Cu3 P nanoparticles (NPs) coated by a N,P-codoped carbon shell that is extended to a hierarchical porous carbon matrix with identical uniform N and P doping (termed Cu3 P@NPPC) as an electrocatalyst. Cu3 P@NPPC demonstrates outstanding activity for both the hydrogen evolution and oxygen reduction reaction, representing the first example of a Cu3 P-based bifunctional catalyst for energy-conversion reactions. The high performances are ascribed to the high specific surface area, the synergistic effects of the Cu3 P NPs with intrinsic activity, the protection of the carbon shell, and the hierarchical porous carbon matrix doped by multiheteroatoms. This strategy of using a diverse MOF as a structural and compositional material to create a new multifunctional composite/hybrid may expand the opportunities to explore highly efficient and robust non-noble-metal catalysts for energy-conversion reactions.

Tuning the functional substituent group and guest of metal–organic frameworks in hybrid membranes for improved interface compatibility and proton conduction

The incorporation of metal–organic frameworks (MOFs) into polymers would be a very promising strategy for overcoming the disadvantage of MOF brittleness and for extending the application of MOFs in proton-conducting materials. Here, we prepare a series of hybrid membranes composed of MOFs and chitosan (CS, very cheap polymer), and systemically study the effect of the incorporation of pure MIL-101 ([Cr3O(H2O)3(bdc)3], bdc = terephthalic acid), the ligand-modified MIL-101, namely S-MIL-101 ([Cr3O(H2O)3(STA)3]·nH2O, STA = 2-sulfoterephthalic acid), and the non-volatile acid-loaded MIL-101, namely acids@MIL-101 (acids = H2SO4, H3PO4 or CF3SO3H), on the interface compatibility and proton conduction of the hybrid membrane. The experimental results revealed the well compatible interfaces between MOF-based materials and the CS matrix because of the hydrogen bond interaction between them, which greatly improved the proton conductivity, activation energy, thermal and mechanical stability, and swelling property of the hybrid membranes. The functionality of MIL-101 is less than that of S-MIL-101 and acids@MIL-101 because of the presence of more hydrogen-bonding sites, proton hopping sites and proton carriers in the latter two types of materials. All MOF-based materials tested (MIL-101, S-MIL-101, and acids@MIL-101) and their hybrid membranes with CS are characterized using field emission scanning electron microscopy (FE-SEM), TEM, EDS, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), and DSC. Fuel cell performances based on these hybrid membranes have been measured. The investigation provides important information for the design of hybrid membranes containing MOFs and polymers.

Robust multifunctional Zr-based metal–organic polyhedra for high proton conductivity and selective CO2 capture

New stable Zr-based metal–organic polyhedra (MOPs) have been designed and constructed through the self-assembly of a designed flexible sulfonate–carboxylate ligand, 1,2-bis(sodium-2-sulfonate-4-carboxyphenoxy)ethane (NaH2L), and the secondary building units (SBUs) of Cp3Zr3(μ3-O)(μ2-OH)3, (Cp = η5-C5H5). The MOPs feature candy-like cages and the anionic sulfonic groups on the organic ligand strengthened the stability of the MOPs (thermal stability and acid and alkali resistance) by forming strong multiple charge-assisted hydrogen bonds with the cationic SBUs. The unique cavities of this 3D porous framework endowed the MOPs with highly selective CO2 capture. The 2D H-bond networks obtained by the connection of coordinated water molecules and free water molecules between the discrete MOPs enabled a high proton conductivity of 1.41 × 10−3 S cm−1 at 30 °C, 98% relative humidity (RH) and a low activation energy of 0.225 eV for the proton transfer.