Sql Topology Research Articles

Regulating the Topologies and Photoresponsive Properties of Lanthanum-Organic Frameworks.

Metal-organic frameworks (MOFs) show potential application in many domains, in which photochromic MOFs (PMOFs) have received enormous attention. Researchers mainly utilize photoactive ligands to build PMOFs. Recently, the mixed electron donating and accepting ligands strategies have also been used to construct PMOFs driven by the electron transfer between nonphotochromic moieties. However, the potential interligand competition inhibits the formation of PMOFs. Therefore, the exploration of single-ligand-guided assembly is conductive for building PMOFs. Considering the existing electron accepting and donating role of pyridyl and carboxyl, the pyridinecarboxyate derived from the fusion of pyridyl and carboxyl units may serve as single ligand to yield PMOFs (Figure 1d). In this work, the coordination assembly of bipyridinedicarboxylate (2,2'-bipyridine-4,4'-dicarboxylic acid, H2bpdc; 1,10-phenanthroline-2,9-dicarboxylic acid, H2pda) and LaCl3 generate two PMOFs, [La(bpdc)(H2O)Cl] (1) and [La(pda)(H2O)2Cl]⋅2H2O (2). Both complexes feature dinuclear lanthanum as building blocks with differences in the connecting number of likers, in which 1 has (4,8)-connected topology and 2 exhibits sql topology. Their structural differences result in the diversities of photoresponsive functionalities. Compared with reported PMOFs built from photoactive ligands and mixed ligands, this study provides new available categories of single ligand for generating PMOFs and tuning the structure and photoresponsive properties via ligand substitution and external photostimulus.

Self‐Calibration Temperature Sensing and Color Tunable Emission in a Bimetallic Lanthanide Metal–Organic Framework

ABSTRACTTemperature in various scientific and industrial applications requires accurate detection and measurement. Herein, a range of novel isostructural lanthanide‐based metal–organic frameworks (Ln‐MOFs), [EuxTb2−x(3,5‐pdc)3(phen)2(H2O)2]n (x = 0, Tb‐MOF; x = 2, Eu‐MOF; x = 0.002, 0.010, 0.020, 0.040, 0.080, EuxTb2−x‐MOF), were solvothermally synthesized using 3,5‐pyridinedicarboxylic acid (3,5‐H2pdc) and 1,10‐phenanthroline (phen) as ligands. Based on binuclear second building units, Ln‐MOFs exhibited 2D layered structure with sql topology. The luminescent properties of series Ln‐MOFs show systematic tuning shifted from green to red by adjusting the ratio of Eu3+ to Tb3+. The temperature sensing experiments showed that Eu0.020Tb1.980‐MOF exhibited self‐calibration temperature response in a range of 293–413 K, achieving maximum relative sensitivity (Sr) 2.46%·K−1 at 413 K, outscoring many state‐of‐the‐art temperature sensors reported in literature. This study poses great promise of the newly designed Eu0.020Tb1.980‐MOF for the ultra‐sensitive temperature sensing in diverse and large‐scale applications.

Stable Cd(II)-based coordination polymer as a multifunctional fluorescent sensor for ascorbic acid, acetylacetone and nitrofuran antibiotics

The concentrations of hazardous volatile organic compounds (VOCs), pharmaceutical antibiotics and biomolecules in water systems are closely related with public health and ecological security. Thus, the convenient and accurate detection of these harmful items can not only reflect the state of human health but also evaluate the level of homologous contamination in the environment. To this end, a new Cd(II)-CP ({[Cd3L2(bmoe)]·DMF}n) with excellent luminescence properties was designed by employing the semi-rigid tricarboxylic acid 4-(2′,3′-dicarboxylphenoxy) (H3L) and N-donor ligand 1,1′-bis(1H-benzimidazolyl) oxydiethane (bmoe). The as-prepared Cd-CP features the unique uninodal sql topology. Benefiting from its great stability in the aqueous system, Cd-CP serves as a versatile multifunctional fluorescent sensor for different analytes, ascorbic acid (AA), nitrofuran antibiotics nitrofurantoin (NFT) and nitrofurazone (NFZ) and acetylacetone (ACAC). The established methods are characterized with impressive low detection limits, ultrafast response time, high sensitivity, strong anti-interference ability, as well as reliable reproducibility. Experimental and theoretical calculation reveals that the collaborative effects of Förster resonance energy transfer (FRET), inner-filter effect (IFE) and photoinduced electron transfer (PET) are the most probable causes behind the quenching of the CP's fluorescence signal.

Magnetic Order Transition of a Two-Dimensional Square-Lattice Electrocatalyst Assembled by Fe-N4 Units: Crucial Role on Oxygen Reduction.

Herein, we theoretically investigate the effect of magnetic orders on electrocatalytic oxygen reduction reaction (ORR) properties on the Fe-N4 site-embedded two-dimensional (2D) covalent organic framework (Fe-N4@COF-C3N2) under realistic environments. The Fe-N4@COF-C3N2 shows a 2D square-lattice (sql) topology with three magnetic order states: one ferromagnetic state (FM) and two antiferromagnetic states (AFM1 and AFM2). Specially, the electrocatalyst in the AFM2 state shows a remarkable onset potential of 0.80 V/reversible hydrogen electrode (RHE) at pH 1, superior to the existing most excellent noble-metal catalysts. Thermodynamically, the onset potential for the 4e- ORR is 0.64 V/RHE at pH 1, with a magnetic state transition process of FM → AFM1 → FM → FM → FM, while at pH 13, the onset potential for the 4e- ORR is 0.54 V/RHE, with the magnetic transition process of FM → FM → AFM1 → FM → FM. Generally, this finding will provide new avenues to rationally design the Fe-N4 electrocatalyst.

Topology Reconfiguration of Anion-Pillared Metal-Organic Framework from Flexibility to Rigidity for Enhanced Acetylene Separation.

Flexible metal-organic framework (MOF) adsorbents commonly encounter limitations in removing trace impurities below gate-opening threshold pressures. Topology reconfiguration can fundamentally eliminate intrinsic structural flexibility, yet remains a formidable challenge and is rarely achieved in practical applications. Herein, a solvent-mediated approach is presented to regulate the flexible CuSnF6-dpds-sql (dpds = 4,4''-dipyridyldisulfide) with sql topology into rigid CuSnF6-dpds-cds with cds topology. Notably, the cds topology is unprecedented and first obtained in anion-pillared MOF materials. As a result, rigid CuSnF6-dpds-cds exhibits enhanced C2H2 adsorption capacity of 48.61 cm3 g-1 at 0.01bar compared to flexible CuSnF6-dpds-sql (21.06 cm3 g-1). The topology transformation also facilitates the adsorption kinetics for C2H2, exhibiting a 6.5-fold enhanced diffusion time constant (D/r2) of 1.71 × 10-3 s-1 on CuSnF6-dpds-cds than that of CuSnF6-dpds-sql (2.64 × 10-4 s-1). Multiple computational simulations reveal the structural transformations and guest-host interactions in both adsorbents. Furthermore, dynamic breakthrough experiments demonstrate that high-purity C2H4 (>99.996%) effluent with a productivity of 93.9mmol g-1 can be directly collected from C2H2/C2H4 (1/99, v/v) gas-mixture in a single CuSnF6-dpds-cds column.

New Mn-CP as a multi-responsive fluorescent probe for ratiometric sensing toward ascorbic acid and turn-off sensing toward nitrofurazone and acetylacetone

The abuse of environmental and biological related molecules, such as small biomolecules, pharmaceutical antibiotics and volatile organic chemicals has become a hotspot issue of global concern. Thus, exploring accurate and effective techniques for monitoring these species remains a major challenge. Here, by employing semi-rigid tetracarboxylate ligand H4edda, one new 2D Mn-based coordination polymer with formula of [Mn2(edda)(phen)2(H2O)2]n (Mn-CP; H4edda = 5,5′-(ethane-1,2-diylbis(oxy)) diisophthalic acid); phen = 1,10-phenanthroline) has been hydrothermally fabricated. The prepared Mn-CP possesses a sql topology with Schläfli symbol of (44·62). Stability research for Mn-CP reveals that it maintains structural stability and initial fluorescence intensity after soaking in water for one week. Moreover, Mn-CP also displays high structural stability in acidic-basic aqueous solution of broad pH scope (1–13) for 48 h. Importantly, photoluminescence measurements indicate that it shows ratiometric fluorescence response to ascorbic acid (AA) as well as turn-off response toward nitrofurazone (NFZ) and acetylacetone (ACAC). The developed fluorescence probe based on Mn-CP shows merits of high selectivity and low detection limits (33.67 nM, 1.43 nM and 2.29 μM for AA, NFZ and ACAC, respectively). The possible mechanisms have been thoroughly explored through exhaustive experimental surveys and theories calculations. The CP-based multi-responsive fluorescent probe designed in this work extends the application of such materials in environmental and biological related fields.

A Copper-Based Metal-Organic Framework for Selective Separation of C2 Hydrocarbons from Methane at Ambient Conditions: Experiment and Simulation.

C2 hydrocarbon separation from methane represents a technological challenge for natural gas upgrading. Herein, we report a new metal-organic framework, [Cu2L(DEF)2]·2DEF (UNT-14; H4L = 4,4',4″,4‴-((1E,1'E,1″E,1‴E)-benzene-1,2,4,5-tetrayltetrakis(ethene-2,1-diyl))tetrabenzoic acid; DEF = N,N-diethylformamide; UNT = University of North Texas). The linker design will potentially increase the surface area and adsorption energy owing to π(hydrocarbon)-π(linker)/M interactions, hence increasing C2 hydrocarbon/CH4 separation. Crystallographic data unravel an sql topology for UNT-14, whereby [Cu2(COO)4]···[L]4- paddle-wheel units afford two-dimensional porous sheets. Activated UNT-14a exhibits moderate porosity with an experimental Brunauer-Emmett-Teller (BET) surface area of 480 m2 g-1 (vs 1868 m2 g-1 from the crystallographic data). UNT-14a exhibits considerable C2 uptake capacity under ambient conditions vs CH4. GCMC simulations reveal higher isosteric heats of adsorption (Qst) and Henry's coefficients (KH) for UNT-14a vs related literature MOFs. Ideal adsorbed solution theory yields favorable adsorption selectivity of UNT-14a for equimolar C2Hn/CH4 gas mixtures, attaining 31.1, 11.9, and 14.8 for equimolar mixtures of C2H6/CH4, C2H4/CH4, and C2H2/CH4, respectively, manifesting efficient C2 hydrocarbon/CH4 separation. The highest C2 uptake and Qst being for ethane are also desirable technologically; it is attributed to the greatest number of "agostic" or other dispersion C-H bond interactions (6) vs 4/2/4 for ethylene/acetylene/methane.

Effect of Polymorphism on the Sorption Properties of a Flexible Square-Lattice Topology Coordination Network.

The stimulus-responsive behavior of coordination networks (CNs), which switch between closed (nonporous) and open (porous) phases, is of interest because of its potential utility in gas storage and separation. Herein, we report two polymorphs of a new square-lattice (sql) topology CN, X-sql-1-Cu, of formula [Cu(Imibz)2]n (HImibz = {[4-(1H-imidazol-1-yl)phenylimino]methyl}benzoic acid), isolated from the as-synthesized CN X-sql-1-Cu-(MeOH)2·2MeOH, which subsequently transformed to a narrow pore solvate, X-sql-1-Cu-A·MeOH, upon mild activation (drying in air or heating at 333 K under nitrogen). X-sql-1-Cu-A·MeOH contains MeOH in cavities, which was removed through exposure to vacuum for 2 h, yielding the nonporous (closed) phase X-sql-1-Cu-A. In contrast, a more dense polymorph, X-sql-1-Cu-B, was obtained by exposing X-sql-1-Cu-(MeOH)2·2MeOH directly to vacuum for 2 h. Gas sorption studies conducted on X-sql-1-Cu-A and X-sql-1-Cu-B revealed different switching behaviors to two open phases (X-sql-1-Cu·CO2 and X-sql-1-Cu·C2H2), with different gate-opening threshold pressures for CO2 at 195 K and C2H2 at 278 K. Coincident CO2 sorption and in situ powder X-ray diffraction studies at 195 K revealed that X-sql-1-Cu-A transformed to X-sql-1-Cu-B after the first sorption cycle and that the CO2-induced switching transformation was thereafter reversible. The results presented herein provide insights into the relationship between two polymorphs of a CN and the effect of polymorphism upon gas sorption properties. To the best of our knowledge, whereas sql networks such as X-sql-1-Cu are widely studied in terms of their structural and sorption properties, this study represents only the second example of an in-depth study of the sorption properties of polymorphic sql networks.

Phthalocyanine Covalent Organic Frameworks: Dimensionality Effect on Third‐Order Nonlinear Optical Properties

AbstractDimensionality of covalent organic frameworks (COFs), in terms of 2D and 3D, must greatly influence their properties and functionalities due to the different electronic and porous structures, but still less investigated in the 20 years history. Herein, on the basis of the imidization reaction of phthalocyanine‐based tetraanhydride monomers with either 1,4‐phenylenediamine or 1,3,5,7‐tetra(4‐aminophenyl)adamantine, 2D and 3D imide‐bonded COFs with sql and pts topology have been prepared to explore their third‐order nonlinear optical (NLO) properties. In contrast to metal‐free analogues, both 2D and 3D copper‐phthalocyanine COFs have the enhanced NLO behaviors according to the open aperture Z‐scan and optical limiting (OL) results recorded under a nanosecond laser at 532 nm. In particular, 2D COFs with strong π–π staking phthalocyanine units show the NLO property with bigger third‐order nonlinear susceptibility (Imχ(3)) and unique reverse saturation absorption response at 1064 nm than that of 3D species with dispersed conjugated modules. Furthermore, femtosecond transient absorption spectra disclose the longer excited lifetimes of copper COFs than metal free samples, helpful in their NLO property. These findings clearly disclose the materials advantages of 2D phthalocyanine COFs toward the NLO characteristics and provide new candidates for OL application.

1D Covalent Organic Frameworks Triggering Highly Efficient Photosynthesis of H2 O2 via Controllable Modular Design.

The topological diversity of covalent organic frameworks (COFs) enables considerable space for exploring their structure-performance relationships. In this study, we report a sequence of novel 1D COFs (EO, ES, and ESe-COF) with typical 4-c sql topology that can be interconnected with VIA group elements (O, S, and Se) via a modular design strategy. It is found that the electronic structures, charge delivery property, light harvesting ability, and hydrophilicity of these 1D COFs can be profoundly influenced by the bridge-linked atom ordinal. Finally, EO-COF, possessing the highest quantity of active sites, the longest lifetime of the active electron, the strongest interaction with O2 , and the lowest energy barrier of O2 reduction, exhibits exceptional photocatalytic O2 -to-H2 O2 activity under visible light, with a production rate of 2675 μmol g-1 h-1 and a high apparent quantum yield of 6.57 % at 450 nm. This is the first systematic report on 1D COFs for H2 O2 photosynthesis, which enriches the topological database in reticular chemistry and promotes the exploration of structure-catalysis correlation.

1D Covalent Organic Frameworks Triggering Highly Efficient Photosynthesis of H2O2 via Controllable Modular Design

AbstractThe topological diversity of covalent organic frameworks (COFs) enables considerable space for exploring their structure‐performance relationships. In this study, we report a sequence of novel 1D COFs (EO, ES, and ESe‐COF) with typical 4‐c sql topology that can be interconnected with VIA group elements (O, S, and Se) via a modular design strategy. It is found that the electronic structures, charge delivery property, light harvesting ability, and hydrophilicity of these 1D COFs can be profoundly influenced by the bridge‐linked atom ordinal. Finally, EO‐COF, possessing the highest quantity of active sites, the longest lifetime of the active electron, the strongest interaction with O2, and the lowest energy barrier of O2 reduction, exhibits exceptional photocatalytic O2‐to‐H2O2 activity under visible light, with a production rate of 2675 μmol g−1 h−1 and a high apparent quantum yield of 6.57 % at 450 nm. This is the first systematic report on 1D COFs for H2O2 photosynthesis, which enriches the topological database in reticular chemistry and promotes the exploration of structure‐catalysis correlation.

Interplay of bipyridine and 4,4′-diaminodiphenylmethane ligands in crystal design of cadmium-based coordination polymers: Structures and unusual photoluminescence quenching

Starting from Cd(ClO4)2·2H2O, four positively charged coordination polymers were prepared and characterized by IR spectroscopic and single-crystal X-ray diffraction methods. The obtained crystalline solids included one-dimensional coordination polymers, {[Cd(dadpm)(2,2′-bpy)2](ClO4)2}n (1), and {[Cd(dadpm)(2,2′-bpy)2](ClO4)2·0.5(H2O)}n (2), and two-dimensional coordination polymers, {[Cd(4,4′-bpy)2(H2O)2](ClO4)2(dadpm)2}n (3), and {[Cd(4,4′-bpy)2(H2O)2](ClO4)2(4,4′-bpy)0.5(dadpm)·EtOH}n (4) (dadpm = 4,4′-diaminodiphenylmethane, 2,2′-bpy = 2,2′-bipyridine; 4,4′-bpy = 4,4′-bipyridine). The similar one-dimensional coordination backbones in 1 and 2 were originated from the mononuclear Cd(II) coordination cores with the N6 distorted octahedral geometries going from two terminal bidentate-chelate 2,2′-bpy and two bidentate-bridging dadpm ligands that mediated the successive metal atoms in coordination chains. The charge-balanced perchlorate anions were located in the interchain space complemented by water molecules in 2. The coordination chains were interconnected into H-bonded networks via NH(NH2)⋯O hydrogen bonds. The 2D coordination polymers 3 and 4 comprised the same positively charged square-grid infinite networks {[Cd(4,4′-bpy)2(H2O)2]2+}n with sql topology and with cadmium atom in the N4O2 tetragonally distorted octahedral coordination geometry as a single node. The charge-compensated ClO4− anions and the dadpm molecules were located in the interlayer space in 3 being complemented by the 4,4′-bpy and EtOH molecules in 4. The solid-state photoluminescence in all reported coordination polymers was significantly attenuated and redistributed along the spectrum in comparison with the pure dadpm which revealed the dual emission in the form of a strong narrow signal in the ultraviolet and a weak signal in the yellow regions of spectrum.

Cu(II) Coordination Polymers Containing Mixed Ligands with Different Flexibilities: Structural Diversity and Iodine Adsorption.

Reactions of N,N'-bis(3-methylpyridyl)oxalamide (L1), N,N'-bis(3-methylpyridyl)adipoamide (L2) and N,N'-bis(3-methylpyridyl)sebacoamide (L3) with tricarboxylic acids and Cu(II) salts afforded {[Cu(L1)(1,3,5-HBTC)]·H2O}n (1,3,5-H3BTC = 1,3,5-benzenetricarboxylic acid), 1, {[Cu1.5(L2)1.5(1,3,5-BTC)(H2O)2]·6.5H2O}n, 2, [Cu(L2)0.5(1,3,5-HBTB)]n (1,3,5-H3BTB = 1,3,5-tri(4-carboxyphenyl)benzene), 3, [Cu4(L3)(OH)2(1,3,5-BTC)2]n, 4, {[Cu3(L3)2(1,3,5-BTB)2]·2.5MeOH·2H2O}n, 5, and {[Cu3(L3)2(1,3,5-BTB)2 ]·DMF·2H2O}n, 6, which have been structurally characterized by using single crystal X-ray crystallography. Complexes 1-4 form a 2D layer with the {44.62}-sql topology, a 2D layer with the (4.62)2(42.62.82)-bex topology, a three-fold interpenetrated 3D net with the (412·63)-pcu topology and a 3D framework with the (410·632·83)(42·6)2(43·63) topology, respectively, whereas 5 and 6 are 3D frameworks with the (63)2(64·82)(68·85·102) topology. Complex 5 shows a better iodine adsorption factor of 290.0 mg g-1 at 60 °C for 360 min than the other ones, revealing that the flexibility of the spacer ligand governs the structural diversity and the adsorption capacity.

A cobalt(II) coordination polymer-derived catalyst engineered via temperature-induced semi-reversible single-crystal-to-single-crystal (SCSC) dehydration for efficient liquid-phase epoxidation of olefins.

Single-crystal-to-single-crystal (SCSC) transformations provide more avenues for phase transitions, which have piqued great interest in crystal engineering. In this work, a 3D Co(II)-based coordination polymer (CP), {Co2(OH2)8(btec)}·4H2O (1), (where (btec)4- = 1,2,4,5-benzenetetracarboxylate) undergoes SCSC transition upon heating at 180 °C to afford an anhydrous phase [Co2(btec)] (1'). Room-temperature water-vapour induced semi-reversible SCSC transformation of 1' involves condensation of two water molecules coordinating to the metal cluster, yielding a new framework [Co2(OH2)2(btec)] (2). These SCSC transitions were accomplished through a sequential bond breaking and new bond formation process which was accompanied by colour changes from orange (1) → violet (1') → pink (2). All materials were structurally elucidated by single-crystal X-ray diffraction (SCXRD) and further established by various analytical techniques. According to SCXRD data, all the frameworks possess octahedral geometries around the cobalt(II) sphere. SCXRD studies further revealed that 1 is a polymeric architecture with a binodal 4-c sql topology while 1' and 2 possess (3,6)-c kgd and (4,6)-c scu 3D nets, respectively. By virtue of multitopicity exhibited by the tetracarboxylate, the coordination number of the linker around the Co(II) sphere increased from four (in 1) to eight (in 1') and then decreased to six (in 2). Most interestingly, permanent porosity could be observed for the dihydrate 2, originated from potential void space as substantiated by dinitrogen (N2) sorption isotherm. These porous frameworks were active catalysts for the aerobic epoxidation of the model substrate cyclohexene using molecular oxygen (O2) as the final oxidant in the presence of the sacrificial i-butyraldehyde (IBA) reductant. For using the dihydrous phase 2, cyclohexene and various other olefins were catalytically oxidised to their corresponding epoxides with up to 38.5% conversion and 99.0% selectivity. The catalyst 2 can be expediently recycled in four runs without significant loss of activity. This research demonstrates that a little innovation in the active-site-engineered organic-inorganic hybrid materials can significantly enhance the catalytic performance and selectivity of coordination polymer-derived heterogeneous catalysts.

New group IIIA metal phosphate-oxalates containing dimethylammonium cations with proton conductivity.

Three new group IIIA metal phosphate-oxalate (MPO) compounds, namely [(CH3)2NH2]2[M2(HPO4)2(H2PO4)2(C2O4)] (M = Al (1), Ga (2)) and [(CH3)2NH2]2[In2(HPO4)2(H2PO4)2(C2O4)]·H2O (3), have been synthesized. Their crystal structures feature an anionic layer with the sql topology net. In particular, 1 displays a proton conductivity (σ) of 9.09 × 10-3 S cm-1 at 85 °C and under 98% relative humidity, which is the highest among MPOs. This study not only endows the main group metal-based MPO family with new members, but also contributes to further understanding of the structure-directing roles of amines and provides a feasible idea for improving the proton conductivity of MPOs.

Construction of 2D layered metal‐organic frameworks based on the norbornene‐derived ligand with fascinating magnetic and luminescent properties

AbstractThree new two‐dimensional metal‐organic frameworks (MOFs), namely [Cu3(NDIC)3 ⋅ C2H5OH ⋅ 2H2O]n (1), [Co2(NDIC)2 ⋅ 2 C3H7NO ⋅ H2O]n ⋅ nC2H5OH (2) and [(Zn3O)2(Zn(H2O)4)(NDIC)6 ⋅ C3H7NO ⋅ C2H5OH ⋅ C2H5O ⋅ 7H2O]n (3) based on the ligand 5‐norbonene‐2,3‐dicarboximide isophthalic acid (H2NDIC) have been synthesized under solvothermal condition, which have been further characterized by single crystal X‐ray diffraction analysis, powder X‐ray diffraction ( PXRD) elemental analysis, ICP, TG and FT‐IR spectroscopy. The ligand displayed distinctive coordination modes to connect mononuclear metal ion, binuclear and trinuclear metal clusters to generate different 2D layered structures in compound 1–3. Compound 1 shows KGM type network based on paddle‐wheel Cu2(COO)4 as secondary building units (SBUs). Compounds 2 and 3 have the undulating 2D (4, 4) SQL topology with the point symbol (44 ⋅ 62) based on Co2(COO)4 and Zn3(μ3‐O)(COO)4 as SBUs, respectively. The magnetic properties of compound 1–2 and the luminescent property of compound 3 and its fluorescent detection for Fe3+ has been investigated and discussed.

Multi-responsive fluorescent sensitivities of a novel 2D Cu-CP with visual turn-off sensing toward nitrofuran antibiotics, Cr(VI) and MnO4− in aqueous solutions

Herein, a novel fluorescent coordination polymer [Cu2(edda)(bpy)2]·6H2O (Cu-CP; H4edda = 5,5′-(ethane-1,2-diylbis(oxy)) diisophthalic acid; bpy = 2,2′-bipyridine) was designed and successfully architected using semi-rigid tetracarboxylic acid ligand H4edda combined with N,N′-donor linker bpy through a hydrothermal method. Single-crystal structural analysis reveals that the adjacent Cu1 centers are linked by 3′- and 5- carboxyl groups of edda4− linker to form a one-dimensional Cu(II)-edda4− chain, which is further strutted by 3- and 5′- carboxyl groups in edda4− ligand to generate a two-dimensional (2D) network with sql topology. Notably, bpy molecules do not actually dedicate to the formation of this 2D network, which merely saturate the configuration of Cu ions. Apart from the great thermal and acid/base stabilities, the π-conjugated nature of H4edda endows Cu-CP with the traits of strong fluorescent emission in both solid state and aqueous solution. Interestingly, Cu-CP can act as a multifunctional platform for effectively detecting nitrofurazone (NFZ), nitrofurantoin (NFT), Cr2O72−, CrO42− and MnO4− via fluorescence quenching effects in an aqueous system. The fabricated Cu-CP fluorescent sensor shows distinguished sensitivity and anti-interference performance as well as low detection limits (3.55 nM for NFZ; 1.02 nM for NFT; 0.58 μM for Cr2O72−, 0.68 μM for CrO42− and 4.59 μM for MnO4−). The underlying quenching mechanisms have been studied through in-depth experimental and computational researches.

Multiresponsive luminescent sensors for antibiotics and CrVI with two luminescent ZnII/CdII coordination complexes

Two new ZnII/CdII luminescent coordination polymers (CPs) based on the V-shaped bis(imidazole) ligand 3,6-bis (1H-benzo[d]imidazol-1-yl)-9-methyl-9H-carbazole (bbimc) with [1,1′-biphenyl]-4,4′-dicarboxylic acid ligand (H2bpdc) have been synthesized under solvothermal conditions: {[Zn(bbimc)(bpdc)]·DMF·2.5H2O} (CP 1), {[Cd(bbimc)(bpdc)]·2DMF} (CP 2). CP 1 and CP 2 both display a uninodal 4-c unimodal sql topology 2D framework with vertex symbols of {44·62}. In addition, the two identical 2D nets of CP 2 were interpenetrated each other to form a 2D + 2D → 3D and generate a 2-fold interpenetrating architecture. Moreover, sensing investigations of CP 1 and CP 2 revealed that both of compounds can be used as a highly sensitive and selective multi-responsive luminescent sensor for sensing Cr2O72−, CrO42− and antibiotics (TC: Tetracycline; CTC: Chlortetracycline) in H2O by exhibiting fluorescence quenching with significant quenching constants (Ksv = 1.369 × 104 M−1 (Cr2O72−), 2.003 × 104 M−1 (CrO42−), 5.343 × 104 M−1 (TC), 8.706 × 104 M−1 (CTC) for CP 1 and 4.452 × 104 M−1 (Cr2O72−), 2.119 × 104 M−1 (CrO42−), 4.175 × 104 M−1 (TC), 1.257 × 105 M−1 (CTC) for CP 2). The detection limit are 0.67 μM (Cr2O72−), 0.48 μM (Cr2O72−), 0.23 μM (TC), 0.14 μM (CTC) for CP 1 and 0.28 μM (Cr2O72−), 0.54 μM (CrO42−), 0.31 μM (TC), 0.098 μM (CTC) for CP 2, respectively. In addition, the probable fluorescence quenching mechanism was studied through experiment and theoretical calculation and the co-existance of competitive absorption (CA) and photoinduced electron transfer (PET) progress contributed to such sensing processes.

N-N-Bridged Polynuclear POM-Based Coordination Polymers Based on a V-Type Ligand: Proton Conduction and Magnetism.

The construction of polyoxometalate (POM)-based coordination polymers, in the presence of a nitrogen heterocyclic ligand, is intriguing due to the potential for obtaining diverse structures. These structures exhibit extensive application possibilities in the fields of proton conductivity and magnetism. Herein, four new POM-based polynuclear coordination polymers with the formulas of {[Fe2(btb)3(H2O)2(SiW12O40)]·3H2O}n (1), {[Cd2(btb)2(H2O)6(HPMoVI10MoV2O40)]·2H2O}n (2), {[Co3(OH)2(btb)2(H2O)5(HPMoVI10MoV2O40)]·7H2O}n (3), and {[Cu3(OH)(btb)2(H2O)(HP2Mo5O23)]·6H2O}n (4) have been prepared using the V-type 1,3-bis(4H-1,2,4-triazole-4-yl)benzene (btb) ligand. Compounds 1 and 2 feature similar two-dimensional (2D) structures, derived from the binuclear Fe2N6 and Cd2N4 subunits connected by tridentate btb ligands. Meanwhile, in compound 3, hexanuclear Co6(OH)4 units are bound by quadridentate btb ligands forming a 2D layer with the same 4-c sql topology simplification as compounds 1 and 2. In compound 1, Keggin-type polyoxoanions are monodentate-coordinated to metal ions and suspended on the 2D structure, while, in compounds 2 and 3, they act as discrete counterions residing in the interstitial spaces between two adjacent layers, thereby extending the 2D structures into 3D structures through hydrogen bonding interactions. In compound 4, trinuclear Cu3(OH) subunits are further constructed into a 3D framework through cooperation with four tridentate and quadridentate btb ligands as well as Strandberg-type anions. Furthermore, the proton conduction of the four compounds has been investigated. They display high proton conductivities at 358 K and 98% RH with powdered samples, which are 1.26 × 10-3, 1.24 × 10-3, 3.24 × 10-4, and 2.57 × 10-4 S cm-1, respectively. Interestingly, by mixing with Nafion, the composite membranes of compounds 2 and 4 exhibit enhanced proton conductivities, measuring at 4.87 × 10-2 and 1.28 × 10-2 S cm-1, respectively, at 358 K and 98% RH, which suggests excellent potential for applications. In addition, compounds 1, 3, and 4 display antiferromagnetic behaviors due to similar magnetic interactions. This work can provide research insights into the assembly of 2D POM-based coordination polymers with nitrogen heterocyclic ligands and Keggin-type POMs and further promote their research progress in proton conduction.

Construction of bifunctional CdII luminescent coordination complexes and efficient detection of Cr2O72− and 2,4,6-trinitrophenol

Three new CdII coordination polymers (CPs) based on a new flexible large π-electron-rich bis(pyridinyl-imidazole) ligand 9,10-bis((2-(pyridin-2-yl)-1H-imidazole-1-yl)methyl)anthracene (bpima) have been synthesized under solvothermal conditions using a mixed-ligand strategy: {[Cd(bpima)0.5(nda)(H2O)]·DMF} (CP 1), {[Cd(bpima)0.5(oba)]·DMF·2H2O} (CP 2), {[Cd(bpima)0.5(ipa)(H2O)]·DMF·2H2O} (CP 3), (H2nda = naphthalene-1,4-dicarboxylic acid; H2oba = 4,4′-oxydibenzoic acid and H2ipa = 5-(tert-butyl)isophthalic acid). CP 1 and CP 2 both feature 2D layer structures with hcb and sql topology, respectively. CP 3 shows 1D ladder-like double-chain structure. In additional, luminescent properties of CP 1 and CP 3 have been systematically investigated and demonstrated multi-responsive luminescent sensitivities. Two compounds can be used for detection of Cr2O72− and 2,4,6-trinitrophenol (TNP) with high sensitivity (High quenching efficiency Ksv: for Cr2O72−: 5.07 × 104 M−1 for CP 1 and 7.38 × 104 M−1 for CP 2; for TNP: 4.87 × 104 M−1 for CP 1 and 5.13 × 104 M−1 for CP 2. low detection limit values: for Cr2O72−: 0.56 μM for CP 1 and 0.38 μM for CP 2; for TNP: 0.63 μM for CP 1 and 0.52 μM for CP 2) and as well as good recyclability. In addition, the sensing mechanism for Cr2O72− and TNP is also discussed by experimental studies and theory calculations, which was attributed to the co-existence of competitive absorption (CA), fluorescence resonance energy transfer (FRET) and photoinduced electron transfer (PET) progress for TNP and CA progress for Cr2O72−, respectively. Moreover, simple fluorescent filter paper based on CP 1 has been developed to achieve detection of Cr2O72− and TNP via the unaided eye, which has great potential for practical applications.