Functionalization of Microporous Lanthanide-Based Metal–Organic Frameworks by Dicarboxylate Ligands with Methyl-Substituted Thieno[2,3-b]thiophene Groups: Sensing Activities and Magnetic Properties

Two Thiophene-Functionalized Co-MOFs as Green Heterogeneous Catalysts for the Biginelli Reaction

Two Co(II) metal-organic frameworks (Co-MOFs), namely, [Co(DMTDC)(bimb)]n (Co-MOF-1) and {[Co(DPTDC)(bimb)(H2O)]·2DMF}n (Co-MOF-2) (H2DMTDC = 3,4-dimethylthieno[2,3-b]thiophene-2,5-dicarboxylic acid, H2DPTDC = 3,4-diphenylthieno[2,3-b]thiophene-2,5-dicarboxylic acid, bimb = 1,4-bis((1H-imidazol-1-yl)methyl)benzene), were obtained by the reaction of flexible N-containing ligand bimb and two structurally related thiophene-containing ligands H2DMTDC and H2DPTDC, respectively. These Co-MOFs displayed a 3D framework and porous structure, respectively. Co-MOF-1 and the activated sample Co-MOF-2' could act as green heterogeneous catalysts for the one-pot multicomponent Biginelli reaction, specifically the dehydration condensation process involving aldehydes, acetoacetates, and urea to yield dihydropyrimidin-2(1H)-ones. The reaction has advantages such as solvent-free conditions, water as only byproduct, readily accessible starting materials, excellent functional group compatibility, and simple operation. Both catalysts exhibited a wide substrate scope and maintained significant catalytic activity over five cycles. The special catalytic performance may be ascribed to functional groups within the ligand.

Thiophene-Functionalized Cadmium(II)-Based Metal-Organic Frameworks for CO2 Adsorption with Gate-Opening Effect, Separation, and Catalytic Conversion

Two new porous three-dimensional cadmium(II) metal-organic frameworks (MOFs) containing thiophene-appended carboxylate acid ligands, formulated as [Cd(L1)(4,4'-Bipy)]n.2n(DMF) (1) and [Cd(L2)(4,4'-Bipy)]n.2n(DMF) (2) [where L1 = 5-{(thiophen-2-ylmethyl)amino}isophthalate, L2 = 5-{(thiophen-3-ylmethyl)amino}isophthalate, 4,4'-Bipy = 4,4'-bipyridine, and DMF = N,N'-dimethylformamide] have been synthesized and structurally characterized. The gas adsorption analysis of the activated MOFs shows that they specifically capture CO2 (uptake amount 4.36 mmol/g under 1 bar at 195 K) over N2 and CH4. Moreover, both MOFs show a gate-opening-closing phenomenon, which features the S-shaped isotherms with impressive hysteretic desorption during the CO2 adsorption-desorption process at 195 K. Ideal adsorbed solution theory (IAST) calculations of these MOFs displayed that the obtained selectivity values for CO2/CH4 (50:50) and CO2/N2 (15:85) are approximately 8.6-23 and 93-565, respectively. Configurational bias Monte Carlo simulation was performed to understand the mechanism behind the better CO2 adsorption by these MOFs. Catalytic activity of the MOFs for the CO2 fixation reactions with different epoxides to form cyclic carbonates were tested. These MOFs demonstrated a significantly high conversion (94-99%) of epichlorohydrin to the corresponding cyclic carbonate within 8 h of reaction time at 1 bar of CO2 pressure, at 70 °C, and they can be reused up to five cycles without losing considerably their activity.

Magnetic properties and magnetocaloric effect of Ln = Dy, Tb carborane-based metal-organic frameworks

We present the synthesis and magneto-thermal properties of carborane-based lanthanide metal-organic frameworks (MOFs) with the formula {[(Ln)3(mCB-L)4(NO3)(DMF)n]·Solv}, where Ln = Dy or Tb, characterized by dc and ac susceptibility, X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD) and heat capacity measurements. The MOF structure is formed by polymeric 1D chains of Ln ions with three different coordination environments (Ln1, Ln2, Ln3) running along the b-axis, linked by carborane-based linkers thus to provide a 3D structure. Static magnetic measurements reveal that these MOFs behave at low temperature as a system of S* = 1/2 Ising spins, weakly interacting ferromagnetically along the 1D polymeric chain (J*/kB = +0.45 K (+0.5 K) interaction constant estimated for Dy-MOF (Tb-MOF)) and coupled to Ln ions in adjacent chains through dipolar antiferromagnetic interactions. The Dy MOF exhibits slow relaxation of magnetization through a thermally activated process, transitioning to quantum tunneling of the magnetization at low temperatures, while both compounds exhibit field-induced relaxation through a very slow, direct process. The maximum magnetic entropy changes (-ΔSmaxm) for an applied magnetic field change of 2-0 T are 5.71 J kg-1 K-1 and 4.78 J kg-1 K-1, for Dy and Tb MOFs, respectively, while the magnetocaloric effect (MCE) peak for both occurs at T ∼ 1.6 K, approximately double that for the Gd counterpart.

A PEDOT enhanced covalent organic framework (COF) fluorescent probe for in vivo detection and imaging of Fe3

Simple and accurate in vivo monitoring of Fe3+ is essential for gaining a better understanding of its role in physiological and pathological processes. A novel fluorescent probe was synthesized via in situ solid-state polymerization of 3,4-ethylenedioxythiophene (PEDOT) in the pore channels of a covalent organic framework (COF). The PEDOT@COF fluorescent probe exhibited an absolute quantum yield (QY) 3 times higher than COF. In the presence of Fe3+ the PEDOT@COF 475 nm fluorescence emission, 365 nm excitation, is quenched within 180 s. Fluorescence quenching is linear with Fe3+ in the concentration range of 0-960 μM, with a detection limit of 0.82 μM. The fluorescence quenching mechanism was attributed to inner filter effect (IEF), photoinduced electron transfer (PET) and static quenching (SQE) between PEDOT@COF and Fe3+. A paper strip-based detector was designed to facilitate practical applicability, and the PEDOT@COF probe successfully applied to fluorescence imaging of Fe3+ levels in vivo. This work details a tool of great promise for enabling detailed investigations into the role of Fe3+ in physiological and pathological diseases.

One Luminescent Cadmium Iodide with Free Bifunctional Azole Sites as a Triple Sensor for Cu2+, Fe3+, and Cr2O72- Ions

The exploration of an excellent triple sensor for monitoring Cu²⁺, Fe³⁺, and Cr₂O₇^2- ions is of exceeding significance because of their serious effects on the human body. Herein, optically active 1H-3,5-bis(pyrazinyl)-1,2,4-triazole (Hbpt) with triazolyl and pyrazinyl groups was applied for the construction of a new type of organic hybrid cadmium iodide [Cd₆I₈(bpt)₄(H₂O)₄]·2H₂O (1) incorporating a hitherto-unknown [Cd₃I₄(H₂O)₂]²⁺ trimeric-cationic unit, which shows an orange light emission at 589 nm with a large Stokes shift of 246 nm. In virtue of the existence of free bifunctional azole sites as the receptors, 1 exhibits a highly selective and sensitive sensing property toward Cu²⁺, Fe³⁺, and Cr₂O₇^2- ions in aqueous solution with lower detection limits of 0.70∼4.46 ppm, which offers the sole example of cadmium iodide as an excellent triple sensor for detecting Cu²⁺, Fe³⁺, and Cr₂O₇^2- ions. Moreover, temperature-dependent luminescent determinations also reveal that 1 can be used as the potential luminescent molecular thermometer.

Influence of the Synthesis and Crystallization Processes on the Cation Distribution in a Series of Multivariate Rare-Earth Metal-Organic Frameworks and Their Magnetic Characterization

The incorporation of multiple metal atoms in multivariate metal-organic frameworks is typically carried out through a one-pot synthesis procedure that involves the simultaneous reaction of the selected elements with the organic linkers. In order to attain control over the distribution of the elements and to be able to produce materials with controllable metal combinations, it is required to understand the synthetic and crystallization processes. In this work, we have completed a study with the RPF-4 MOF family, which is made of various rare-earth elements, to investigate and determine how the different initial combinations of metal cations result in different atomic distributions in the obtained materials. Thus, we have found that for equimolar combinations involving lanthanum and another rare-earth element, such as ytterbium, gadolinium, or dysprosium, a compositional segregation takes place in the products, resulting in crystals with different compositions. On the contrary, binary combinations of ytterbium, gadolinium, erbium, and dysprosium result in homogeneous distributions. This dissimilar behavior is ascribed to differences in the crystallization pathways through which the MOF is formed. Along with the synthetic and crystallization study and considering the structural features of this MOF family, we also disclose here a comprehensive characterization of the magnetic properties of the compounds and the heat capacity behavior under different external magnetic fields.

Designed synthesis of an sp2 carbon-conjugated fluorescent covalent organic framework for selective detection of Fe3

A new fully conjugated covalent organic framework material (COF_TFPPy-ThDAN) has been synthesized via the Knoevenagel condensation reaction using 1,3,6,8-tetra(4-formylphenyl)pyrene (TFPPy) as the chromogenic unit and 2,2'-([2,2'-bithiophene]-5,5'-diyl)diacetonitrile (ThDAN) as the linker. The COF_TFPPy-ThDAN has been successfully prepared under the optimized conditions and showed excellent crystallinity and chemical stability. Especially, it was able to maintain its crystallinity even when immersed under harsh conditions such as HCl (3 M) and NaOH (3 M). Meanwhile, COF_TFPPy-ThDAN exhibited good fluorescence properties, which could remain relatively stable under different pH conditions. Moreover, COF_TFPPy-ThDAN was further employed for the detection of Fe³⁺ with high sensitivity and selectivity with a limit of detection (LOD) of 1.26 μM. COF_TFPPy-ThDAN with high stability and fluorescence is a promising material for chemical sensing.

Two Multiresponsive Luminescent Zn-MOFs for the Detection of Different Chemicals in Simulated Urine and Antibiotics/Cations/Anions in Aqueous Media

Two Zn-MOFs, namely, {[Zn(L)_0.5(bpea)]·0.5H₂O·0.5DMF}_n [LCU-113 (for Liaocheng University)] and {[Zn(L)_0.5(ibpt)]·H₂O·DMF}_n (LCU-114), were synthesized based on flexible tetracarboxylic acid 1,3-bis(3,5-dicarboxyphenoxy)benzene (H₄L) and different N-ligands [bpea = 1,2-dipyridyl ethane; ibpt = 3-(4'-imidazolobenzene)-5-(pyridine-4'-yl)-1,2,4-triazole]. LCU-113 and LCU-114 possess twofold interpenetrating three-dimensional pillared layer structures, in which a two-dimensional layer formed by carboxylic acid and Zn²⁺ ions was pillared by bpea and ibpt, respectively. The two complexes show high water stability and high luminescence sensing performance toward organic solvents, ions, and antibiotics, as well as chemicals, in simulated urine. The investigation showed that (1) LCU-113 and LCU-114 could detect uric acid (UA, 2,6,8-trihydroxypurine, metabolite of purine) and p-aminophenol (PAP, biomarker of phenamine) in simulated urine by luminescence quenching, respectively, and (2) luminescence quenching of LCU-113 and LCU-114 occurred in aqueous solutions of nitrofurazone (NZF), Fe³⁺, and CrO₄^2-/Cr₂O₇^2-. All the above detections have excellent anti-interference ability and recyclability. The luminescence mechanism analysis indicates that weak interactions between the framework structures and the target analytes as well as the energy competition (inner filter effect) play an important role in sensing the above analytes. The practical application for monitoring NZF/Fe³⁺ in water samples was also tested.

A Water-Stable 2-Fold Interpenetrating cds Net as a Bifunctional Fluorescence-Responsive Sensor for Selective Detection of Cr(III) and Cr(VI) Ions

Reactions of ZnSO₄∙7H₂O, N-(pyridin-3-ylmethyl)-4-(pyridin-4-yl)-1,8-naphthalimide (NI-mbpy-34), and 5-bromobenzene-1,3-dicarboxylic acid (Br-1,3-H₂bdc) afforded a luminescent coordination polymer, [Zn(Br-1,3-bdc)(NI-mbpy-34)]_n (1), under hydro(solvo)thermal conditions. Single-crystal X-ray structure analysis revealed that 1 features a three-dimensional (3-D) 2-fold interpenetrating cds (or CdSO₄) net topology with the point symbol of (6⁵·8), where the Zn(II) centers are considered as 4-connected square-planar nodes. X-ray powder diffraction (XRPD) patterns and thermogravimetric (TG) analysis confirmed that 1 shows high chemical and thermal stabilities. Notably, 1 displayed solvent dependent photoluminescence properties; the fluorescence intensity and emission maximum of 1 in different solvent suspensions varied when a solvent was changed. Furthermore, the H₂O suspension of 1 exhibited blue fluorescence emission and thus can be treated as a selective and sensitive fluorescent probe for turn-on detection of Cr³⁺ cations through absorbance caused enhancement (ACE) mechanism and turn-off detection of Cr₂O₇²⁻/CrO₄²⁻ anions through collaboration of the absorption competition and energy transfer process, with limit of detection (LOD) as low as μM scale.

Gd(III)-based metal-organic frameworks and coordination polymers for magnetic refrigeration

As the alternatives of expensive and increasingly shortage 3He for ultralow-temperaturerefrigeration, molecule-based magnetorefrigerant materials have attracted much attention in the past decades. Among them, Gd(III)-based metal-organic frameworks and coordination polymers...

Three Silver(I) Coordination Polymers Based on Pyridyl Ligands and Auxiliary Carboxylic Ligands: Luminescence and Efficient Sensing Properties

Easily producible sensors for harmful industrial waste compounds are of significant interest for both human health and the environment. Three novel coordination polymers, [Ag(μ-aca)(μ₄-bztpy)_1/2] (1), [Ag(μ-bza)(μ-bpa)] (2), and [Ag₂(μ-aca)₂(μ-bpa)₂]·EtOH·2H₂O (3), were assembled in this study by reactions using Ag⁺ as a node with the pyridyl ligand 1,2,4,5-tetrakis(4-pyridyl)benzene (bztpy) or 9,10-bis(4-pyridyl)anthracene (bpa) and an auxiliary chelating carboxylic ligand. Single-crystal X-ray structural analyses revealed that compound 1 has a 3D framework consisting of 1D [Ag(aca)]_∞ chains and bztpy linkers, while 2 and 3 have 2D layered structures consisting of binuclear Ag-carboxylate units and bpa linkers, respectively. Topological studies revealed that 1 has a bbf topology, while 2 and 3 are 2D [4,4] rhombic grids. The compounds were further characterized by powder X-ray diffraction, IR, elemental analysis, thermogravimetric analysis, and a luminescence study. The solids of 1-3 exhibited intense photoluminescent emission with λ_em^max at ca. 493, 472, and 500 nm, respectively. Remarkably, due to their excellent framework stability, 1 and 2 can act as multiresponsive luminescent sensors for nitrobenzene, Fe³⁺, and Cr₂O₇^2- with a high selectivity and sensitivity ascribed to their quenching effect.

An investigation of affecting factors on MOF characteristics for biomedical applications: A systematic review

Metal-organic frameworks (MOFs) are a fascinating class of crystalline porous materials composed of metal ions and organic ligands. Due to their attractive properties, MOFs can potentially offer biomedical field applications, such as drug delivery and imaging. This study aimed to systematically identify the affecting factors on the MOF characteristics and their effects on structural and biological characteristics. An electronic search was performed in four databases containing PubMed, Scopus, Web of Science, and Embase, using the relevant keywords. After analyzing the studies, 20 eligible studies were included in this review. As a result, various factors such as additives and organic ligand can influence the size and structure of MOFs. Additives are materials that can compete with ligand and may affect the nucleation and growth processes and, consequently, particle size. The nature and structure of ligand are influential in determining the size and structure of MOF. Moreover, synthesis parameters like the reaction time and initial reagents ratio are critical factors that should be optimized to regulate the size and structure. Of note is that the nature of the ligand and using a suitable additive can control the porosity of MOF. The more extended ligands aid in forming large pores. The choice of metallic nodes and organic ligand, and the MOF concentration are important factors since they can determine toxicity and biocompatibility of the final structure. The physicochemical properties of MOFs, such as hydrophobicity, affect the toxicity of nanoparticles. An increase in hydrophobicity causes increased toxicity of MOF. The biodegradability of MOF, as another property, depends on the organic ligand and metal ion and environmental conditions like pH. Photocleavable ligands can be served for controlled degradation of MOFs. Generally, by optimizing these affecting factors, MOFs with desirable properties will be obtained for biomedical applications.

An ultra-sensitive selective fluorescent sensor based on a 3D zinc-tetracarboxylic framework for the detection and enrichment of trace Cu2+ in aqueous media

Herein, a novel and fluorescent zinc-organic framework sensor [Zn₃(μ₃-Hbptc)₂(μ₂-4,4'-bpy)₂(H₂O)₄]_n·2nH₂O (1) (H₄bptc = 2,3,3',4'-biphenyl tetracarboxylic acid, 4,4'-bpy = 4,4'-bipyridine) is synthesized and characterized, demonstrating its excellent fluorescence performance for Cu²⁺ detection and the enrichment of Cu²⁺ in aqueous media. The fluorescence intensity of 1 can be selectively quenched by Cu²⁺ in a linear range of Cu²⁺ concentrations of 0-0.7 μM. The limit of detection (LOD) value is as low as 32.4 nM, which is superior to those of most of the fluorescent sensors based on metal-organic frameworks (MOFs). It is also far below the maximum allowable concentration of Cu²⁺ in drinking water as defined by the U.S. Environmental Protection Agency (EPA) and the World Health Organization (WHO), so it is employed for the detection of Cu²⁺ in actual water samples. More importantly, the nature of the interaction between the active coordination site (COO^-) of 1 and Cu²⁺ determines the quenching mechanism, that is Cu²⁺ in the analyte is captured by MOF 1, which has been investigated by ICP, luminescence, UV-vis, XPS, and lifetime studies. Besides, the chemosensor shows regeneration performance without the loss of performance in five consecutive cycles. So MOF 1 is a simple and convenient probe used not only for the rapid detection but also for the enrichment of trace amounts of Cu²⁺ in aqueous media, and the application can be further extended to a variety of environmental and biological analysis processes.

Engineered Bifunctional Luminescent Pillared-Layer Frameworks for Adsorption of CO2 and Sensitive Detection of Nitrobenzene in Aqueous Media

Through a dual-ligand synthetic approach, five isoreticular primitive cubic (pcu)-type pillared-layer metal-organic frameworks (MOFs), [Zn₂ (dicarboxylate)₂ (NI-bpy-44)]⋅x DMF⋅y H₂ O, in which dicarboxylate=1,4-bdc (1), Br-1,4-bdc (2), NH₂ -1,4-bdc (3), 2,6-ndc (4), and bpdc (5), have been engineered. MOFs 1-5 feature twofold degrees of interpenetration and have open pores of 27.0, 33.6, 36.8, 52.5, and 62.1 %, respectively. Nitrogen adsorption isotherms of activated MOFs 1'-5' at 77 K all displayed type I adsorption behavior, suggesting their microporous nature. Although 1' and 3'-5' exhibited type I adsorption isotherms of CO₂ at 195 K, MOF 2' showed a two-step gate-opening sorption isotherm of CO₂ . Furthermore, MOF 3' also had a significant influence of amine functions on CO₂ uptake at high temperature due to the CO₂ -framework interactions. MOFs 1-5 revealed solvent-dependent fluorescence properties; their strong blue-light emissions in aqueous suspensions were efficiently quenched by trace amounts of nitrobenzene (NB), with limits of detection of 4.54, 5.73, 1.88, 2.30, and 2.26 μm, respectively, and Stern-Volmer quenching constants (K_sv ) of 2.93×10³ , 1.79×10³ , 3.78×10³ , 4.04×10³ , and 3.21×10³  m^-1 , respectively. Of particular note, the NB-included framework, NB@3, provided direct evidence of the binding sites, which showed strong host-guest π-π and hydrogen-bonding interactions beneficial for donor-acceptor electron transfer and resulting in fluorescence quenching.

A series of lanthanide(III) metal-organic frameworks derived from a pyridyl-dicarboxylate ligand: single-molecule magnet behaviour and luminescence properties

The reactions of LnIII ions with a versatile pyridyl-decorated dicarboxylic acid ligand lead to the formation of a series of novel three-dimensional (3D) Ln-MOFs, [Ln3(pta)4(Hpta)(H2O)]·xH2O (Ln = Dy (1), Eu (2), Gd (3), Tb (4), H2pta = 2-(4-pyridyl)-terephthalic acid, x = 6 for 1, 2.5 for 2, 1.5 for 3 and 2 for 4). The Ln3+ ions act as nine-coordinated muffin spheres, linking to each other to generate trinuclear {Ln3(OOC)6N2} SBUs, which are further extended to be interesting 3D topological architectures. To the best of our knowledge, the Dy-MOF exhibits zero-field single-molecule magnet (SMM) behaviour with the largest effective energy barrier among the previously reported 3D MOF-based Dy-SMMs. The combined analyses of a diluted sample (1@Y) and ab initio calculations demonstrate that the thermally assisted slow relaxation is mainly attributed to the single-ion magnetism. Furthermore, fluorescence measurements reveal that H2pta can sensitize EuIII and TbIII characteristic luminescence.

Magnetic Tunability in RE-DOBDC MOFs via NOx Acid Gas Adsorption

The magnetic susceptibility of NO_x-loaded RE-DOBDC (rare earth (RE): Y, Eu, Tb, Yb; DOBDC: 2,5-dihydroxyterephthalic acid) metal-organic frameworks (MOFs) is unique to the MOF metal center. RE-DOBDC samples were synthesized, activated, and subsequently exposed to humid NO_x. Each NO_x-loaded MOF was characterized by powder X-ray diffraction, and the magnetic characteristics were probed by using a VersaLab vibrating sample magnetometer (VSM). Lanthanide-containing RE-DOBDC (Eu, Tb, Yb) are paramagnetic with a reduction in paramagnetism upon adsorption of NO_x. Y-DOBDC has a diamagnetic moment with a slight reduction upon adsorption of NO_x. The magnetic susceptibility of the MOF is determined by the magnetism imparted by the framework metal center. The electronic population of orbitals contributes to determining the extent of magnetism and change with NO_x (electron acceptor) adsorption. Eu-DOBDC results in the largest mass magnetization change upon adsorption of NO_x due to more available unpaired f electrons. Experimental changes in magnetic moment were supported by density functional theory (DFT) simulations of NO_x adsorbed in lanthanide Eu-DOBDC and transition metal Y-DOBDC MOFs.

Formation and Encapsulation of Lead Halide Perovskites in Lanthanide Metal-Organic Frameworks for Tunable Emission

Improving the stability of perovskite quantum dots and adjusting their optical properties are essential for their application in advanced optoelectronic equipment. We provide a simple synthetic method to hybridize perovskite quantum dots and metal-organic frameworks (MOFs) into a polymer matrix. The hybrid material is made by encapsulating perovskite CH₃NH₃PbBr₃ quantum dots in lanthanide-based metal-organic frameworks. A series of lanthanide-based metal-organic frameworks (LnMOFs), namely, [Ln(tpob)(DMF)(H₂O)]_n (Lntpob, Ln = Nd, Sm, Eu, Gd, Tb, Dy, H₃tpob = 1,3,5-tris(4-carbonylphenyloxy)benzene), have been synthesized under solvothermal conditions and fully characterized. Lntpobs display a three-dimensional (3D) pcu network with central-symmetric [Eu₂(COO)₄] structural building units (SBUs) linked by one-dimensional (1D) chains. CH₃NH₃PbBr₃@Eutpob hybrids were developed through a three-step process, in which the precursor PbBr₂@Eutpob was formed by immersing the Eutpob crystal synthesized in the first step into a PbBr₂ solution; then the composite materials could form quickly when CH₃NH₃Br was added to the precursor. Therefore, the hybrid composite material exhibits luminescent properties related to the excitation wavelength in the form of powders or thin films. In addition, the photoluminescence of the CH₃NH₃PbBr₃@Eutpob composite can be improved and maintained for a long time after it is introduced into the poly(methyl methacrylate) (PMMA) matrix. Moreover, the emission peak based on the perovskite quantum dots can still maintain about 85% of the original intensity after being left for 30 days. Also, the obtained PMMA films can achieve tunable emission from red to green.

Novel alkaline earth metal–organic frameworks with thiophene groups for selective detection of Fe3+

This work demonstrates that the alkaline earth ion radii play an important role in coordination numbers and topologies for constructing MOFs, and these MOFs can be used as fast-response fluorescence sensors for the detection of Fe³⁺.

Dual-responsive luminescent sensors based on two Cd-MOFs: rare enhancement toward acac and quenching toward Cr2O72−

Two luminescent Cd-MOFs were employed as dual-responsive luminescence sensors to detect acac and Cr₂O₇²⁻ through turn-on and turn-off mechanisms.

A highly robust heterometallic TbIII/NiII-organic framework for C2 hydrocarbon separation and capture

The exquisite combination of hetreometallic [TbIIINiII(COO)3(H2O)] clusters with a designed hexatopic ligand generates one highly robust three-dimensional heterometallic TbIII/NiII-organic framework material {[TbNi(HTDP)(H2O)]·3DMF·2H2O}n (NUC-2; H6TDP = 2,4,6-tri(2,4-dicarboxyphenyl)pyridine). Gas adsorption measurements reveal that the activated NUC-2 exhibits ultrahigh C2H2 adsorption capacity but negligible uptake of C2H4, which is ascribed to its high stability and ultrahigh functional internal surface. Furthermore, dynamic breakthrough experiments confirm that NUC-2 can effectively fulfill the separation of a C2H2/C2H4 (1 : 99) mixture. Such excellent performance makes NUC-2 a promising adsorbent for practical C2H2/C2H4 separation and provides new insights into heterometallic MOFs for gas separation.

From lamellar net to bilayered-lamella and to porous pillared-bilayer: reversible crystal-to-crystal transformation, CO2 adsorption, and fluorescence detection of Fe3+, Al3+, Cr3+, MnO4−, and Cr2O72− in water

Layered coordination polymers of different network topologies have showed reversible structural transformations and fluorescence detection toward Fe³⁺, Al³⁺, Cr³⁺, MnO₄^–, and Cr₂O₇^2– in water.

A new 3D four-fold interpenetrated dia-like luminescent Zn(ii)-based metal–organic framework: the sensitive detection of Fe3+, Cr2O72−, and CrO42− in water, and nitrobenzene in ethanol

A four-fold interpenetrating Zn-MOF as a multi-responsive fluorescent sensor for Fe³⁺, Cr₂O₇²⁻, and CrO₄²⁻ ions in water, and NB in ethanol is reported.

Assembly of four new cobalt coordination polymers modulated by N-coligands: sensitive and selective sensing of nitroaromatics, Fe3+and Cr2O72−in water

Four new Co-CPs (1to4) have been obtained with the modulation of N-coligands.2and3can serve as multi-responsive sensors for rapid and sensitive detection of nitroaromatics, Fe³⁺and Cr₂O₇²⁻in water.

A novel (3,6)-connected CdII coordination polymer based on an ether-linked tricarboxylate ligand: synthesis, topology and luminescence sensing properties in aqueous solution

A novel three-dimensional coordination polymer, namely, poly[[diaquabis(μ-4,4'-bipyridine)bis{μ₃-5-[(2-carboxyphenoxy)methyl]isophthalato}tricadmium(III)] dimethylformamide monosolvate 2.5-hydrate], {[Cd₃(C₁₆H₉O₇)₂(C₁₀H₈N₂)₂(H₂O)₂]·2C₃H₇NO·5H₂O}_n, was obtained by the reaction of ether-linked 5-[(2-carboxyphenoxy)methyl]isophthalic acid (H₃L) with Cd^II salts in the presence of 4,4'-bipyridine (bpy) under solvothermal conditions. In this complex, the Cd^II centres are connected by the carboxylate ligands to form two-dimensional wave-like layers, which are pillared by bpy ligands and extended into a rare three-dimensional (3,6)-connected sqc27 framework. The complex demonstrated good water stability and strong luminescence emissions. It not only possesses excellent luminescence sensing activities toward Fe³⁺ and Cr₂O₇^2- in aqueous solution, but can also distinguish between Cr₂O₇^2- and CrO₄^2- by luminescence. Furthermore, it could be simply and quickly regenerated at least five times. A study of the sensing mechanism indicated that luminescence quenching may be related to the energy competition between the complex and sensing analytes.

A dual-emitting Tb(iii)&Yb(iii)-functionalized coordination polymer: a "turn-on" sensor for N-methylformamide in urine and a "turn-off" sensor for methylglyoxal in serum

Fluorescent materials with lanthanide cations encapsulated in MOFs are currently used in numerous applications, especially in biosensors. Therefore, herein, two novel composites were designed and developed based on a Tb(iii)&Yb(iii)-functionalized Cu(ii)-coordination polymer, possessing higher thermal and water stability and fascinating fluorescence properties. The first bimetallic composite Tb@Cu-Hcbpp demonstrated broad ligand-centered emission and weak typical Tb³⁺ ion emission; moreover, it was used as an excellent ratiometric fluorescent sensor for the metabolic product NMF of DMF in the human body (LOD = 0.02 μM). In addition, the Yb³⁺ ions were doped into Tb@Cu-Hcbpp to improve the fluorescence performance of the green Tb³⁺ ion emission. Among the series of Tb_1-xYb_x@Cu-Hcbpp samples (x = 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35 and 0.40), Tb_0.85Yb_0.15@Cu-Hcbpp showed maximum enhanced fluorescence intensity (almost 9.6 times that of the pure terbium system), but exhibited high fluorescence quenching efficiency for methylglyoxal (MGO), which could be used for the sensitive detection of MGO (LOD = 0.25 μM). Furthermore, the developed biosensors were successfully applied for the detection of NMF and MGO in urine and serum samples, and satisfactory results were obtained, showing good potential of these biosensors in practical applications such as in disease diagnosis and biochemical research.

A nanoporous metal-organic framework as a renewable size-selective hydrogen-bonding catalyst in water

A novel squaramide-containing metal-organic framework (MOF) material has been designed and synthesized. A detailed X-ray crystal structure analysis showed that four squaramides of this MOF adopted two orientations in each dependent nanopore, confirming that two carbonyl and two N-H groups pointed simultaneously to the inside of the one-dimensional nanometer channel. The MOF was applied as an efficient bifunctional hydrogen-bonding catalyst for Michael additions of 1,3-dicarbonyl compounds to nitroalkenes in pure water, boosting the catalytic efficiency by up to approximately five times the value afforded by the homogeneous control and exhibiting a highly size-selective catalytic performance and good renewability. The catalytic mechanism was also discussed in detail. The present study provides a highly promising approach to achieving dual-activation catalytic centers in a single system, which function as microscopic chemical reactors that allow the interaction and fast transport of substrate molecules in their cavities.

Temperature-Controlled Assembly/Reassembly of Two Dicarboxylate-Based Three-Dimensional Co(II) Coordination Polymers with an Antiferromagnetic Metallic Layer and a Ferromagnetic Metallic Chain

Two new dicarboxylate-based three-dimensional cobalt coordination polymers, [Co(Me₂mal)(bpe)_0.5(H₂O)]_n (1) and [Co(Me₂mal)(bpe)_0.5]_n (2), were synthesized from dimethylmalonic acid (H₂-Me₂mal) in temperature-controlled solvothermal reactions. Lower temperatures (6080 °C) favored the formation of 1, while higher temperatures (120 °C) favored the production of 2. Compound 1 is comprised of Co(II) corrugated layers linked by syn-anti carboxylate bridges from the Me₂mal^2- ligands and pillared through bis-monodentate bpe groups. Compound 2 is comprised of a three-dimensional network involving one-dimensional Co-carboxylate chains bonded by antisymmetric µ₄-Me₂mal^2- ligands and aligned parallel to the [001] direction. The solvothermal retreatment of crystalline samples of 1 in a DMF/H₂O solvent at 120 °C allowed the structural reassembly, with complete conversion within 2 over 48 h. Magnetic analyses revealed that compound 1 exhibits both spin-orbital coupling and antiferromagnetic interactions through a syn-anti carboxylate (Me₂mal^2-) bridge exchange pathway [Co-Co separation of 5.478 Å] and compound 2 showed a ferromagnetic interaction resulting from the short Co-Co separation (3.150 Å) and the small Co-O-Co bridging angles (98.5° and 95.3°) exchange pathway which was provided by µ₄-Me₂mal^2- bridging ligand.