Regulating luminescence thermal enhancement in negative thermal expansion metal-organic frameworks

Overcoming thermal quenching is generally essential for the practical application of luminescent materials. It has been recently found that frameworks with negative thermal expansion (NTE) could be a promising candidate to engineer unconventional luminescence thermal enhancement. However, the mechanism through which luminescence thermal enhancement can be well tuned remains an open issue. In this work, enabled by altering ligands in a series of UiO-66 derived Eu-based metal-organic frameworks, it was revealed that the changes in the thermal expansion are closely related to luminescence thermal enhancement. The NTE of the aromatic ring part favors luminescence thermal enhancement, while contraction of the carboxylic acid part plays the opposite role. Modulation of functional groups in ligands can change the thermal vibration of aromatic rings and then achieve luminescence thermal enhancement in a wide temperature window. Our findings pave the way to manipulate the NTE and luminescence thermal enhancement based on ligand engineering.

Base-Directed Formation of Isostructural Lanthanide-Sulfate-Glutarate Coordination Polymers with Photoluminescence

A series of five isostructural 3D lanthanide-based coordination polymers [LnIII2(H2O)6(glu)(SO4)2]n [Ln = Pr(1), Nd(2), Sm(3), Eu(4), and Gd(5)] was effortlessly obtained within a few minutes via the microwave-heating method. The employment of auxiliary bases, that is, sodium hydroxide, 4,4'-bipyridine, and 1,4-diazabicyclo[2.2.2]octane, led to the formation of the title complex, whereas base-free synthesis yielded a three-dimensional inorganic coordination polymer, [Ln2(H2O)4(SO4)3]n·nH2O, Ln = Nd (2a). The robustness of the synthetic method was illustrated as both microwave-heating and conventional hydrothermal techniques also enabled the formation of a high-crystalline phase-pure complex 1-5. In the structure of 1-5, glutarato (glu2-) and sulfato ligands link dinuclear Ln(III) building units into three-dimensional frames. The glu2- ligands act as tethering linkers, expanding the structure into a neutral 3D coordination network. Hydrogen bonds were found to be the predominant intermolecular interactions in the crystal structures. Photoluminescence of the complex 1-5 was studied.

Fluorescence detection platform of metal-organic frameworks for biomarkers

Sensitive and selective detection of biomarkers is crucial in the study and early diagnosis of diseases. With the continuous development of biosensing technologies, fluorescent biosensors based on metal-organic frameworks have attracted increasing attention in the field of biomarker detection due to the combination of the advantages of MOFs, such as high specific surface area, large porosity, and structure with tunable functionality and the technical simplicity, sensitivity and efficiency and good applicability of fluorescent detection techniques. Therefore, researchers must understand the fluorescence response mechanism of such fluorescent biosensors and their specific applications in this field. Of all biomarkers applicable to such sensors, the chemical essence of nucleic acids, proteins, amino acids, dopamine, and other small molecules account for about a quarter of the total number of studies. This review systematically elaborates on four fluorescence response mechanisms: metal-centered emission (MC), ligand-centered emission (LC), charge transfer (CT), and guest-induced luminescence change (GI), presenting their applications in the detection of nucleic acids, proteins, amino acids, dopamine, and other small molecule biomarkers. In addition, the current challenges of MOFs-based fluorescent biosensors are also discussed, and their further development prospects are concerned.

[α-AsW9O33]9- bridged hexagonal clusters of Ln(III) showing field induced SMM behavior: experimental and theoretical insight

Polyoxometalates (POM), as inorganic polydentate oxygen donors, provide binding opportunities for oxophilic lanthanide metal centers to construct novel Ln-substituted POM materials with exciting structures and attractive properties. Herein, we have reported four arsenotungstate [α-AsW₉O₃₃]^9- based lanthanide-containing polyoxometalates [Cs_xK_36-x{Ln₆(H₂O)₁₂(α-AsW₉O₃₃)₆}]·yH₂O (Ln = Er (1), Gd (2), Ho (3), and Tb (4)), which are synthesized in an alkaline medium. Complexes 1-3 are the dimeric structures of [Ln₃(H₂O)₆(α-AsW₉O₃₃)₃]^18- polyanions, whereas complex 4 is a hexamer of the polyanion [Tb (H₂O)₂(α-AsW₉O₃₃)]^6- as a building unit. In all the complexes, [α-AsW₉O₃₃]^9- units are staggered up and down and give rise to the chair conformation, where one [α-AsW₉O₃₃]^9- unit bridges two Ln(III) centers through four μ₂-oxygen and two terminal oxygen atoms, resulting in the hexagonal arrangement of lanthanides. The dynamic magnetic measurement indicates that only complex 1 exhibits slow relaxation of magnetization with an applied dc field (1500 Oe). To gain insight into the slow relaxation of magnetization in complex 1, the ligand-field parameters and the splitting of the ground-state multiplet of the Er(III) ions have been estimated. The ab initio calculation results confirm that the ground state wave function of these molecules (1, 3, and 4) is mainly composed of a mixture of m_J states, and the non-axial crystal field (CF) terms are more predominant than the axial CF term. The solid-state fluorescence spectra of 1-4 reveal that the photoexcitation O → M ligand-to-metal charge-transfer (LMCT) of arsenotungstate fragments is effectively quenched due to the spatial coordination environment around the Ln(III) ion.

Detection of anthrax biomarker and metallic ions in aqueous media using spherical-shaped lanthanide infinite coordination polymers

We report a lanthanide-based infinite coordination polymer (ICP) system synthesized using pyrazole-3,5-dicarboxylic acid as linker, malonic acid as coordination modulator and water as solvent. The precursors self-assembly into microspherical particles, which are water-stable and exhibit excellent dispersibility. Bimetallic samples based on Tb³⁺ doped with Eu³⁺ were investigated as ratiometric dipicolinic acid (DPA) sensors, which is a biomarker for Bacillus anthracis spores. Along with the calibration curves, a detection in a real sample extracted from Bacillus subtilis (model organism) was performed. The samples proved to be highly sensitive and selective for ratiometric DPA detection. In a secondary study, the monometallic sample containing only Tb³⁺ was also investigated as a sensor for ionic species in aqueous media. The Cr³⁺, Fe³⁺, Cu²⁺, and Cr₂O₇^2- ionic species could be detected in water by luminescence quenching mechanism. Therefore, we found that the reported ICP system can be judiciously constructed in order to act as a multimodal probe for several chemical species.

Color tunable of Ln-MOFs (Ln = Tb, Eu) and excellent stability for white light-emitting diode

White light-emitting diodes (WLEDs) possess the advantages of environmental friendliness, long lifetime, and energy saving. Recently, metal-organic frameworks (MOFs) have become one of the hot candidates for LEDs. However, the tunable color and thermal stability of MOFs are urgent problems for their actual applications. In this work, Ln-MOFs (Ln = Eu, Tb) were synthesized by a facile wet chemical route. A series of Ln-MOFs phosphors with tunable luminescence color showed potential applications in white LEDs. The emission color of the phosphors can be easily modulated by changing the molar ratio of the raw materials. The luminescence intensities of Ln-MOFs retained over 90.6% of the initial value, showing excellent thermal stability of Ln-MOFs. In order to explore the potential applications of Ln-MOFs in WLEDs, we mixed them with two kinds of blue phosphors and packaged them to obtain WLEDs. The CIE coordinates of both were (0.31, 0.33) and (0.31, 0.34), which were able to achieve white light emission. The peak shape and peak position in the EL spectrum of the WLEDs device remained stable when increasing the applied current of the device. Meanwhile, the white light with excellent color quality and visual performance was achieved. The results show that Ln-MOFs are potential materials for white light LED, and provide a novel idea for the application of Ln-MOFs materials in the luminescence field.

Four series of lanthanide coordination polymers based on the tetrabromobenzene-1,4-dicarboxylate ligand: structural diversity and multifunctional properties

Four series of lanthanide-based coordination polymers (LnCPs), namely [Ln(Br₄bdc)_1.5(MeOH)₃] (1Ln; Ln = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy), [Ln₂(Br₄bdc)₂(NO₃)₂(MeOH)₄] (2Ln; Ln = Ce, Pr, Nd, Sm), [Ln(Br₄bdc)(NO₃)(MeOH)] (3Ln; Ln = Gd, Tb, Dy), and [Ln₂(Br₄bdc)₃(H₂O)_2.3(MeOH)_2.7] (4Ln; Ln = Gd, Tb, Dy) have been synthesized by reacting hydrated lanthanide(III) salts with tetrabromobenzene-1,4-dicarboxylic acid (H₂Br₄bdc) in different solvents under solvothermal conditions. The structural diversity found in the system mainly resulted from the effects of anions, solvents, and the variation in the ionic radii of the lanthanide(III) ions. Compounds in series 1Ln feature a two-dimensional (2D) layered structure with sql topology based on {(Ln(COO)₂)₂(μ-COO)₂} secondary building units (SBUs). Compounds in series 2Ln and 3Ln comprise, respectively, infinite uniform and alternate chains of {Ln(COO)₂}_n SBUs that are assembled into a similar network topology to 1Ln. Meanwhile, compounds in series 4Ln feature 3D coordination networks of a pcu α-Po topological net consisting of binuclear {Ln₂(COO)₃} SBUs. The formation of polymeric networks in series 1Ln-4Ln is facilitated by the numerous coordination sites of the ligand Br₄bdc^2- and the fact that its bromine atoms can participate in the formation of various types of intermolecular interactions. The solid-state photoluminescence studies on Eu- (1Eu) and Tb- (1Tb, 3Tb, 4Tb) containing compounds indicate that the Br₄bdc^2- ligands can efficiently sensitize Eu³⁺ and Tb³⁺ emission. Notably, such compounds exhibit highly sensitive fluorescence sensing for acetone, water, and Fe³⁺ ions via the fluorescence quenching effect. As the representatives of the series, activated 1Eu, 2Pr, 3Tb, and 4Tb show the maximum CO₂ uptake capacities of 170.4, 273.7, 255.3, and 303.5 cm³ g^-1, respectively, at 50 bar and 298 K with good repeatability of the adsorption-desorption properties. Magnetic studies indicate that the Gd- and Dy-based compounds 1Gd, 1Dy, 3Gd, 3Dy, and 4Gd show simple paramagnetic behaviours, whereas compound 4Dy exhibits weak ferromagnetic interactions.

Metal-Organic Framework-Based Materials for Adsorption and Detection of Uranium(VI) from Aqueous Solution

The steady supply of uranium resources and the reduction or elimination of the ecological and human health hazards of wastewater containing uranium make the recovery and detection of uranium in water greatly important. Thus, the development of effective adsorbents and sensors has received growing attention. Metal-organic frameworks (MOFs) possessing fascinating characteristics such as high surface area, high porosity, adjustable pore size, and luminescence have been widely used for either uranium adsorption or sensing. Now pertinent research has transited slowly into simultaneous uranium adsorption and detection. In this review, the progress on the research of MOF-based materials used for both adsorption and detection of uranium in water is first summarized. The adsorption mechanisms between uranium species in aqueous solution and MOF-based materials are elaborated by macroscopic batch experiments combined with microscopic spectral technology. Moreover, the application of MOF-based materials as uranium sensors is focused on their typical structures, sensing mechanisms, and the representative examples. Furthermore, the bifunctional MOF-based materials used for simultaneous detection and adsorption of U(VI) from aqueous solution are introduced. Finally, we also discuss the challenges and perspectives of MOF-based materials for uranium adsorption and detection to provide a useful inspiration and significant reference for further developing better adsorbents and sensors for uranium containment and detection.

Lanthanide-mediated tuning of electronic and magnetic properties in heterotrimetallic cyclooctatetraenyl multidecker self-assemblies

The synthesis of a novel family of homoleptic COT-based heterotrimetallic self-assemblies bearing the formula [LnKCa(COT)₃(THF)₃] (Ln(iii) = Gd, Tb, Dy, Ho, Er, Tm, and Yb) is reported followed by their X-ray crystallographic and magnetic characterization. All crystals conform to the monoclinic P2₁/c space group with a slight compression of the unit cell from 3396.4(2) ų to 3373.2(4) ų along the series. All complexes exhibit a triple-decker structure having the Ln(iii) and K(i) ions sandwiched by three COT²⁻ ligands with an end-bound {Ca²⁺(THF)₃} moiety to form a non-linear (153.5°) arrangement of three different metals. The COT²⁻ ligands act in a η⁸-mode with respect to all metal centers. A detailed structural comparison of this unique set of heterotrimetallic complexes has revealed consistent trends along the series. From Gd to Yb, the Ln to ring-centroid distance decreases from 1.961(3) Å to 1.827(2) Å. In contrast, the separation of K(i) and Ca(ii) ions from the COT-centroid (2.443(3) and 1.914(3) Å, respectively) is not affected by the change of Ln(iii) ions. The magnetic property investigation of the [LnKCa(COT)₃(THF)₃] series (Ln(iii) = Gd, Tb, Dy, Ho, Er, and Tm) reveals that the Dy, Er, and Tm complexes display slow relaxation of their magnetization, in other words, single-molecule magnet (SMM) properties. This behaviour is dominated by thermally activated (Orbach-like) and quantum tunneling processes for [DyKCa(COT)₃(THF)₃] in contrast to [ErKCa(COT)₃(THF)₃], in which the thermally activated and Raman processes appear to be relevant. Details of the electronic structures and magnetic properties of these complexes are further clarified with the help of DFT and ab initio theoretical calculations.

A new class of heterotrimetallic COT-based self-assemblies accommodates metals from groups I–III in three different oxidation states and enables tuning of electronic and magnetic properties.

Highly luminescent mixed-ligand bimetallic lanthanoid(III) complexes for photovoltaic applications

Six new mixed-ligand bimetallic complexes [Eu₂(bz)₄(tta)₂(phen)₂] (1), [Gd₂(bz)₄(tta)₂(phen)₂] (2), [EuTb(bz)₄(tta)₂(phen)₂] (3), [EuGd(bz)₄(tta)₂(phen)₂] (4), [Eu_1,2Gd_0,8(bz)₄(tta)₂(phen)₂] (5) and [Eu_1,6Gd_0,4(bz)₄(tta)₂(phen)₂] (6) have been prepared with the Eu³⁺, Gd³⁺ and Tb³⁺ ions and the benzoate (bz^-), 2-thenoyltrifluoroacetonate (tta^-) and the 1,10-phenanthroline (phen) ligands. The compounds combine highly efficient antennas to obtain highly luminescent complexes to enhance solar cell efficiency. The benzoate ligand has been chosen to take its advantage as a bridging ligand to end up with bimetallic complexes to study the effect of combining two metal ions in the luminescent molecule. The structure of 1 was obtained by single-crystal X-ray diffraction, and 1-6 were found to be isostructural by powder X-ray diffraction analysis. The photophysical properties were studied by the absorbance and emission spectra and emission lifetimes. The magnetic properties of 2 were studied, and we found intramolecular antiferromagnetic interactions between the Gd³⁺ ions. We prepared luminescent down-shifting layers (LDSL) with the 1, 3-6 complexes embedded in ethylene-vinyl-acetate and studied their effect in the external quantum efficiency (EQE) and intensity-voltage (I-V) plots of a solar mini-module. We found that LDSL containing the bimetallic complexes 3 and 6 enhance the efficiency of the solar mini-module from 11.26(3)% to 11.76(4)% (+0.52%) and to 11.44(2)% (+0.21%), respectively.

Understanding the ZIF-L to ZIF-8 transformation from fundamentals to fully costed kilogram-scale production

The production of MOFs at large scale in a sustainable way is key if these materials are to be exploited for their promised widespread application. Much of the published literature has focused on demonstrations of preparation routes using difficult or expensive methodologies to scale. One such MOF is nano-zeolitic imidazolate framework-8 (ZIF-8) - a material of interest for a range of possible applications. Work presented here shows how the synthesis of ZIF-8 can be tracked by a range of methods including X-ray diffraction, thermo gravimetric analysis and inelastic neutron scattering - which offer the prospect of in-line monitoring of the synthesis reaction. Herein we disclose how the production of nano-ZIF-8 can be conducted at scale using the intermediate phase ZIF-L. By understanding the economics and demonstrating the production of 1 kg of nano-ZIF-8 at pilot scale we have shown how this once difficult to make material can be produced to specification in a scalable and cost-efficient fashion.

Recent advancement in bimetallic metal organic frameworks (M’MOFs): Synthetic challenges and applications

Metal-organic frameworks (MOFs) is a burgeoning research field and has received increasing interest in recent years due to their inherent advantages of inorganic metal ions, range of organic linkers, tunable...

Structure, magnetic properties and spin density of two alternative Mn(II) coordination polymers based on 1,4-bis(2'-carboxyphenoxy)benzene

Two novel manganese coordination polymers [Mn2(µ2-bcpb)(µ4-bcpb)(2,2’-bipy)2]n (1) and [Mn2(µ3-bcpb)2(2,2’-bipy)2(H2O)]n (2) (H2bcpb=1,4-bis(2’-carboxylato phenoxy)-benzene; 2,2’-bipy=2,2’-bipyridine), have been synthesized successfully from the same reactants but for different filling degrees of Teflon tubes used...

Photochromism and photoswitchable luminescence in a Zn7 cluster-based metal-organic framework with an organic guest

Photochromic materials coupled with photoswitchable luminescence functionalities are of particular interest due to their potential applications in switches and optical memory devices. However, the construction of such materials, especially those with two-color emission states, is still challenging. In this context, a rare Zn₇ cluster-based host-guest MOF material, (bbmp)[Zn₇(IPA)₆(OH)₄(H₂O)₂] (1) (H₂IPA = isophthalic acid, bbmp·2I = 4,4'-([1,1'-biphenyl]-4,4'-diyl)bis(1-methylpyridin-1-ium) diiodide), was prepared by encapsulating an organic cation into an anionic MOF produced from zinc cations and isophthalic acid ligands, which exhibits reversible naked detectable photochromic properties varying from yellow to green upon UV-Vis light irradiation. The photoactive guest bbmp²⁺ and the short O⋯N⁺ distances between the oxygen atoms of the carboxylate groups and the pyridine ring play a crucial role in the photochromism of this compound. More interestingly, the luminescence color of this cluster-based host-guest material can be reversibly switched from green to blue upon irradiation, exhibiting photoswitchable luminescence properties.

Lanthanide-Organic Frameworks Featuring Three-Dimensional Inorganic Connectivity for Multipurpose Hydrocarbon Separation

Implementation of lanthanide-organic frameworks (LOFs) as solid adsorbents has been frequently handicapped by their permanent porosity being difficult to establish owing to the remarkable flexibility and diversity of lanthanide ions in terms of coordination number and geometry. Construction of robust LOFs with permanent porosity for industrially important hydrocarbon separation will greatly expand their application potential. In this work, by distributing N and O donors into an m-terphenyl skeleton, we rationally synthesized a heterofunctional linker, and constructed a pair of isostructural LOFs. Due to the inclusion of a rarely observed three-dimensional metal-carboxylate backbone serving as a highly connected inorganic secondary building unit, their permanent porosities were successfully established by diverse gas isotherms. They can be applied as separating media not only for natural gas purification and removal of carbon dioxide from C₂ hydrocarbons but also more importantly for single-step ethylene (C₂H₄) purification from a three-component C₂H_n mixture during the adsorption process. The latter separation is very challenging and has been less reported in the literature. This work provides a unique example of LOFs featuring three-dimensional inorganic connectivity applied to multipurpose hydrocarbon separations.

Tb3+-Doped Ag-MOFs for fluorescent detection of formaldehyde in a novel smartphone platform and its removal applications in milk products and wastewater

As one kind of reactive carbonyl species (RCS), formaldehyde (FA) with a high concentration could be extremely toxic to living bodies as well as the environment. This paper reports a three-dimensional (3D) Tb3+@Ag-MOFs-based fluorescent probe for fast sensing of FA, which uses a novel turn-on mechanism based on the luminescence induced by Tb3+. The MOF sensor shows broad dynamic ranges of 0.1-1 mM for FA with the detection limit of 1.9 μM. For online and real-time detection of FA, a portable smartphone platform was employed to analyze the RGB values of the fluorescence by a smartphone application. By incorporating this probe into a polyacrylonitrile (PAN) layer, we synthesized a film composite that could effectively remove FA in real samples including milk and chemical factory wastewater, and the removal rate reached 98.52% and 95.38% respectively. Moreover, the potential of the film to remove gaseous FA was confirmed by experiments as well.

Engineering Near-Infrared-Excitable Metal-Organic Framework for Tumor Microenvironment Responsive Therapy

Luminescent metal-organic frameworks (MOFs), which incorporate some guest luminescent molecules/ions into MOFs, have attracted extensive attention because of their exceptional optical properties. However, traditional luminescent MOFs are mainly responsive to ultraviolet (UV) or visible light, which has limited their bioapplications due to the restrained tissue penetration depths. In this study, we have constructed a diagnostic nanoplatform UCNP@MOF consisting of upconverting metal-organic frameworks, which combine the photo-upconverting characteristics of the upconversion nanoparticles (UCNPs) with the unique physicochemical properties of Al-MOFs. Specifically, the core-shell structured UCNP@MOF nanocomposites were prepared by poly(vinylpyrrolidone) (PVP)-regulated nucleation of Al-MOF layer on the UCNP surface. When excited by a 980 nm laser light, the green signal released from UCNPs can trigger the photosensitive Al-MOFs to produce a large amount of singlet oxygen (¹O₂) for photodynamic therapy (PDT). Meanwhile, the anticancer drug, doxorubicin hydrochloride (DOX), was further incorporated into the porous structures of Al-MOFs and demonstrated the pH-responsive drug release behavior. Our results show that the near-infrared (NIR) light-induced PDT with chemotherapy (CMT) exhibits excellent antitumor effects. It is believed that the present work highlights the potential of the combination of UCNPs and MOFs and holds great promise for biomedical applications.

The coordination chemistry of benzhydrazide with lanthanide(iii) ions: hydrothermal in situ ligand formation, structures, magnetic and photoluminescence sensing properties

The influence of synthetic conditions on the solid-state structural formation of lanthanide(iii) complexes based on a hydrazide ligand have been investigated and reported. Depending on the solvents and reaction temperatures, the reactions of hydrated Ln(NO₃)₃ with a benzohydrazide (bzz) ligand afforded three classes of lanthanide(iii) coordination complexes viz. [Ln(bzz)(NO₃)](NO₃)₂ (1Ln; Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5)), [Ln(bzz)(ben)₃(H₂O)]·H₂O (2Ln; Ln = Pr (6), Nd (7), Sm (8), Eu (9), Gd (10), Tb (11), Dy (12), Er (13)), and [Ln₃(ben)₃] (3Ln; Ln = Eu (14), Gd (15), Tb (16), Dy (17), Er (18), Tm (19), Yb (20), Lu (21)). Complexes 1-5 in series 1Ln were isolated by slow evaporation of their isopropanol solutions at ambient temperature, and the complexes display similar discrete structures bearing distinct intermolecular N-H⋯O hydrogen bonds to generate a three-dimensional (3D) supramolecular architecture. Complexes 6-13 in series 2Ln were obtained under hydrothermal conditions at 110 °C where the in situ generated benzoate (ben) ligands participated in the formation of one-dimensional (1D) coordination polymers (CPs) with the bzz ligands. At a temperature of 145 °C the hydrothermal conditions result in the formation of the thermodynamically more stable products of 14-21 in series 3Ln, in which the bzz ligand underwent complete in situ hydrolysis to create the ben ligand. These coordination assemblies feature 1D zigzag chains that are formed by unusual low coordination numbers of the six- and seven-fold coordinated Ln³⁺ centers bridged by the ben ligands in μ ₂- and μ ₃-coordination modes. Notably, the chain structures of 2Ln can be transformed into the zigzag tape-like structures of 3Ln upon heating the crystalline samples to 400 °C in air. In the solid state at room temperature, the Eu- (2, 9, 14) and Tb- (4, 11, 16) containing complexes emit red and green light, respectively. The luminescence investigations show that the Eu- (9, 14) and Tb-(11, 16) based CPs could be used as fluorescent probes for acetone and Co²⁺ ions via an energy competition mechanism. Meanwhile, the Gd- (10, 15) and Dy- (12, 17) based CPs show typical antiferromagnetic interactions.

Structure-Property Relationships in Photoluminescent Bismuth Halide Organic Hybrid Materials

Seven novel bismuth(III)-halide phases, Bi₂Cl₆(terpy)₂·0.5(H₂O) (1), Bi₂Cl₄(terpy)₂(k₂-TC)₂(2) (TC = 2-thiophene monocarboxylate), BiCl(terpy)(k₂-TC)₂ (3A-Cl), BiBr(terpy)(k₂-TC)₂ (3A-Br), BiCl(terpy)(k₂-TC)₂ (3B-Cl), [BiCl(terpy)(k₂-TC)₂][Bi(terpy)(k₂-TC)₃]·0.55(TCA) (4), [BiBr₃(terpy)(MeOH)] (5), and [BiBr₂(terpy)(k₂-TC)][BiBr_1.16(terpy)(k₂-TC)_1.84] (6), were prepared under mild synthetic conditions from methanolic/aqueous solutions containing BiX₃ (X = Cl, Br) and 2,2':6',2″-terpyridine (terpy) and/or 2-thiophene monocarboxylic acid (TCA). A heterometallic series, 3A-Bi_1-xEu_xCl, with the general formula Bi_1-xEu_xCl(terpy)(k₂-TC)₂ (x = 0.001, 0.005, 0.01, 0.05) was also prepared through trace Eu doping of the 3A-Cl phase. The structures were determined through single-crystal X-ray diffraction and are built from a range of molecular units including monomeric and dimeric complexes. The solid-state photoluminescent properties of the compounds were examined through steady-state and time-resolved methods. While the homometallic phases exhibited broad green to yellow emission, the heterometallic phases displayed yellow, orange, and red emission that can be attributed to the simultaneous ligand/Bi-halide and Eu centered emissions. Photoluminescent color tuning was achieved by controlling the relative intensities of these concurrent emissions through compositional modifications including the Eu doping percentage. Notably, all emissive homo- and heterometallic phases exhibited rare visible excitation pathways that based on theoretical quantum mechanical calculations are attributed to halide-metal to ligand charge transfer (XMLCT). Through a combined experimental and computational approach, fundamental insight into the structure-property relationships within these Bi halide organic hybrid materials is provided.

Recent advances in colorimetry/fluorimetry-based dual-modal sensing technologies

Tailored to the increasing demands for sensing technologies, the fabrication of dual-modal sensing technologies through combining two signal transduction channels into one method has been proposed and drawn considerable attention. The integration of two sensing signals not only promotes the analytical efficiency with reduced assumption, but also improves the analytical performances with enlarged detection linear range, enhanced accuracy, and boosted application flexibility. The two top-rated output signals for developing dual-modal sensors are colorimetric and fluorescent signals because of their outstanding merits for point of care applications and real-time sensitive sensing. Given the rapid development of material chemistry and nanotechnology, the recent decade has witnessed great advance in colorimetric/fluorimetric signal based dual-modal sensing technologies. The new sensing strategy leads to a broad avenue for various applications in disease diagnosis, environmental monitoring and food safety because of the complementary and synergistic effects of the two output signals. In this state-of-the-art review, we comprehensively summarize different types of colorimetric/fluorimetric dual-modal sensing methods by highlighting representative research in the last 5 years, digging into their sensing methodologies, particularly the working principles of the signal transduction systems. Then, the challenges and future prospects for boosting further development of this research field are discussed.

Beyond structural motifs: the frontier of actinide-containing metal-organic frameworks

In this perspective, we feature recent advances in the field of actinide-containing metal-organic frameworks (An-MOFs) with a main focus on their electronic, catalytic, photophysical, and sorption properties. This discussion deviates from a strictly crystallographic analysis of An-MOFs, reported in several reviews, or synthesis of novel structural motifs, and instead delves into the remarkable potential of An-MOFs for evolving the nuclear waste administration sector. Currently, the An-MOF field is dominated by thorium- and uranium-containing structures, with only a few reports on transuranic frameworks. However, some of the reported properties in the field of An-MOFs foreshadow potential implementation of these materials and are the main focus of this report. Thus, this perspective intends to provide a glimpse into the challenges, triumphs, and future directions of An-MOFs in sectors ranging from the traditional realm of gas sorption and separation to recently emerging areas such as electronics and photophysics.

Statistic Replacement of Lanthanide Ions in Bis-salicylatoborate Coordination Polymers for the Deliberate Control of the Luminescence Chromaticity

Based on the strand-like coordination polymer (CP) type 1 ∞ [Ln(BSB)3 (py)2 ], [BSB]- =bis-salicylatoborate anion, mixed Eu/Tb-containing compounds of the constitution 1 ∞ [Eux Tb1-x (BSB)3 (py)2 ] were synthesised ionothermally for a phase width of (x=0.25-0.75) and characterized regarding structure and optical properties. Previously, known only for other lanthanides, the mixed 1D-Eu/Tb-CPs show excellent options for statistic replacement of the Ln-cations during synthesis yielding solid solutions. The products are highly luminescent, with the chromaticity being a direct function of the amount of the respective Ln-ions. Corresponding to an overall addition of emission intensities, the green Tb3+ emission and the red Eu3+ emission allow for a chromaticity control that also includes yellow emission. Control of the luminescence colour renders them suitable examples of the versatility of statistic replacement of metal ions in coordination chemistry. In addition, crystallization of [EMIm]2 [YCl5 (py)] illuminates possible other products of the ionothermal reactions of [EMIm][BSB] with LnCl3 constituted by components not being part of the main CPs.

The effect of terminal N-donor aromatic ligands on the sensitization and emission of lanthanide ions in Zn2Ln (Ln = Eu, Tb) complexes with 4-biphenylcarboxylate anions

The systematic series of trinuclear carboxylate complexes [Zn₂Ln(NO₃)(phbz)₆(L)₂] (Ln = Eu, Gd, and Tb, where phbz is the anion of 4-biphenylcarboxylic acid, and L is pyridine, 2,3-lutidine or 2,2′-bipyridine) were synthesized. Luminescence properties were investigated in detail.

Recent progress in lanthanide metal–organic frameworks and their derivatives in catalytic applications

Research progress in lanthanide metal–organic frameworks and their derivatives in the field of catalysis has been presented on the basis of different organic reactions.

A new 2D lanthanum based microporous MOF for efficient synthesis of cyclic carbonates through CO2 fixation

We report a new microporous La-MOF La-5-SIP-MOF through solvothermal reaction and it showed high catalytic activity for the synthesis of cyclic carbonates from epoxides via the CO₂ fixation reaction at room temperature.

Luminescent metal–organic frameworks as chemical sensors based on “mechanism–response”: a review

The comprehensive review systematically summarizes the recent developments in the study of LMOFs as chemical sensors based on “mechanism–response”.

Luminescence tuning and sensing properties of stable 2D lanthanide metal–organic frameworks built with symmetrical flexible tricarboxylic acid ligands containing ether oxygen bonds

New Ln-MOFs were yielded by a flexible ligand and lanthanide ions. The colors can be regulated by adjusting the molar ratios of Eu³⁺/Tb³⁺, showing promising applications in NB sensing, tunable photoluminescence and pH sensing.

A tetraphenylethylene-based covalent organic framework for waste gas adsorption and highly selective detection of Fe3+

A tetraphenylethylene-based covalent organic framework shows an outstanding performance for waste gas adsorption and has good selectivity and detection effect for Fe3+.

The role of metal–organic porous frameworks in dual catalysis

Metal–organic frameworks (MOFs) are a valuable group of porous crystalline solids with inorganic and organic parts that can be used in dual catalysis.

Visual Luminescent Probes Constructed by Eu3+ Complex-Functionalized Silica Nanocomposites and Their Langmuir-Blodgett Films at Interfaces

The trivalent europium ion (Eu³⁺) has garnered a great deal of interest for the design of luminescent materials possessing compound-independent emission bands, strong luminescent intensity, and long emission lifetimes. We herein introduce a synthetic methodology capable of constructing visual luminescent probes from Eu³⁺ complex-functionalized silica nanocomposites and their Langmuir-Blodgett (LB) films at interfaces. In order to facilitate the coordinative stabilization of Eu³⁺ over carrier surfaces, silica nanoparticles (nanoSiO₂) were pregrafted with terpyridyl (TPy) to make nanoSiO₂TPy linkers. Then, a well-designed coordination reaction of nanoSiO₂TPy with EuCl₃ and 2,6-pyridinedicarboxylic acid (DPA) was carried out at solid-liquid and air-water interfaces, where our desired material (denoted as nanoSiO₂TPy@EuDPA) and its corresponding LB film are obtained. The presence of TPy and DPA interacting with Eu³⁺ plays a key role in regulating the chemical nature of the particle surface, hence giving rise to closely packed nanocomposite arrays in the film. As a result, the improvement in uniformity and stability is achieved alongside the enhancement in emission intensity and lifetime. With such advantageous optical properties, we find them workable as facile, green, and affordable luminescent sensors, by which a range of common toxic anions (Cr₂O₇^2-, MnO₄^-, and PO₄^3-) can be visually and quantitatively recognized. Notably, the LB film-based material could afford a higher K_sv value (1.53 × 10⁵ M^-1), a lower detection limit (0.157 μM), and better recyclability than its original powder analogue, showcasing its utility as a more promising candidate for practical use.

Halogenated Terephthalic Acid "Antenna Effects" in Lanthanide-SURMOF Thin Films

Lanthanide-based crystalline coatings have a great potential for energy-conversion devices, but until now luminescent surface-anchored materials were difficult to fabricate. Thin films, called lanthanides surface-mounted metal-organic frameworks (SURMOFs) with tetrasubstituted halide (fluorine, chlorine, and bromine) terephthalic acid derivative linkers as a basic platform for optical devices, exhibit a high quantum yield of fluorescence visible to the naked eyes under ambient light. We show that we can tune the luminescent properties in thin films by halide substitution, which affords control over the molecular structure of the material. We rationalize the mechanism for the modulation of the photophysical properties by "antenna effect", which controls the energy transfer and quantum yields using experimental and theoretical techniques for chelated lanthanides as a function of the type of atom substitutions at the phenyl rings and the resulting dihedral angle between phenyl rings in the linkers and carboxylate groups.

Effect of Larger Pore Size on the Sorption Properties of Isoreticular Metal-Organic Frameworks with High Number of Open Metal Sites

Four isostructural CPO-54-M metal-organic frameworks based on the larger organic linker 1,5-dihydroxynaphthalene-2,6-dicarboxylic acid and divalent cations (M=Mn, Mg, Ni, Co) are shown to be isoreticular to the CPO-27 (MOF-74) materials. Desolvated CPO-54-Mn contains a very high concentration of open metal sites, which has a pronounced effect on the gas adsorption of N2 , H2 , CO2 and CO. Initial isosteric heats of adsorption are significantly higher than for MOFs without open metal sites and are slightly higher than for CPO-27. The plateau of high heat of adsorption decreases earlier in CPO-54-Mn as a function of loading per mole than in CPO-27-Mn. Cluster and periodic density functional theory based calculations of the adsorbate structures and energetics show that the larger adsorption energy at low loadings, when only open metal sites are occupied, is mainly due to larger contribution of dispersive interactions for the materials with the larger, more electron rich bridging ligand.

Colorimetry of Luminescent Lanthanide Complexes

Europium, terbium, dysprosium, and samarium are the main trivalent lanthanide ions emitting in the visible spectrum. In this work, the potential of these ions for colorimetric applications and colour reproduction was studied. The conversion of spectral data to colour coordinates was undertaken for three sets of Ln complexes composed of different ligands. We showed that Eu is the most sensitive of the visible Ln ions, regarding ligand-induced colour shifts, due to its hypersensitive transition. Further investigation on the spectral bandwidth of the emission detector, on the wavelengths’ accuracy, on the instrumental correction function, and on the use of incorrect intensity units confirm that the instrumental correction function is the most important spectrophotometric parameter to take into account in order to produce accurate colour values. Finally, we established and discussed the entire colour range (gamut) that can be generated by combining a red-emitting Eu complex with a green-emitting Tb complex and a blue fluorescent compound. The importance of choosing a proper white point is demonstrated. The potential of using different sets of complexes with different spectral fingerprints in order to obtain metameric colours suitable for anti-counterfeiting is also highlighted. This work answers many questions that could arise during a colorimetric analysis of luminescent probes.

A dual emission metal-organic framework for rapid ratiometric fluorescence detection of CO3 2- in seawater

A dual emission metal-organic framework (IRMOF-10-Eu) was prepared and used as a ratiometric fluorescent sensor for CO₃ ^2- detection. IRMOF-10-Eu had good stability and excellent luminescence in aqueous solution. IRMOF-10-Eu showed dual fluorescence emission from the ligand and Eu³⁺ with single excitation. Upon treatment with CO₃ ^2-, the fluorescence ratio (I ₆₂₄/I ₃₅₈) of the probe displayed significant change. The relative fluorescence intensity ratio (I ₆₂₄/I ₃₅₈) and CO₃ ^2- concentration had a linear relationship in 50-300 μM range with a low detection limit of 9.58 μM. And the luminescence probe of CO₃ ^2- showed a fast detection time. The possible mechanism was investigated. CO₃ ^2- changed the structure of IRMOF-10-Eu and interrupted the energy transfer process. Thus, the fluorescence emission intensity of the ligand was increased and Eu³⁺ was decreased with the addition of CO₃ ^2-. IRMOF-10-Eu was used to detect CO₃ ^2- in seawater, which showed good prospect in practical application. Subsequently, a highly selective and sensitive probe, IRMOF-10-Eu, may pave an efficient way for CO₃ ^2- detection in seawater.

Dual-emitting barium based metal-organic nanosheets as a potential sensor for temperature and anthrax biomarkers

The development of novel 2D materials, due to the promising applications they have enabled through their unique properties, has attracted increasingly more research interest. In this regard, novel dual-emitting coordination polymer nanosheets were developed by doping Eu³⁺ and Tb³⁺ ions into the nanostructures of the [Ba(DPA)₂(H₂O)₂] _n (DPA = dipicolinic acid) coordination polymer (BCP). Single crystal x-ray crystallography revealed that BCP is a 1D coordination polymer and its three-dimensional supramolecular architecture is constructed with a relatively strong hydrogen bonding in the ac crystallographic plane and weak non-covalent interactions along the b axis. Using energetic ultrasound irradiations, synthesis of nanoscale BCP along with the unzipping of the weak interactions between the ac layers was accomplished. The resulting BCP nanosheets was used as the host lattice and was doped with Eu³⁺ and Tb³⁺ ions. Remarkably, the sensing ability of both Eu³⁺ and Tb³⁺ doped coordination polymer (Ln@BCP) nanosheets towards temperature and the DPA anthrax biomarker were investigate. The high relative sensitivity value of 2.42% K^-1 and their reusability, makes Ln@BCP nanosheets an ideal candidate for the nanothermometry. They also exhibited high selective detection characteristics towards the DPA anthrax biomarker with a 0.03 nM detection limit. Therefore, Ln@BCP nanosheets can also be considered as an efficient multi-responsive optical sensor.

Rational Construction of Porous Metal-Organic Frameworks for Uranium(VI) Extraction: The Strong Periodic Tendency with a Metal Node

Although metal-organic frameworks (MOFs) have been reported as important porous materials for the potential utility in metal ion separation, coordinating the functionality, structure, and component of MOFs remains a great challenge. Herein, a series of anionic rare earth MOFs (RE-MOFs) were synthesized via a solvothermal template reaction and for the first time explored for uranium(VI) capture from an acidic medium. The unusually high extraction capacity of UO₂²⁺ (e.g., 538 mg U per g of Y-MOF) was achieved through ion-exchange with the concomitant release of Me₂NH₂⁺, during which the uranium(VI) extraction in the series of isostructural RE-MOFs was found to be highly sensitive to the ionic radii of the metal nodes. That is, the uranium(VI) adsorption capacities continuously increased as the ionic radii decreased. In-depth mechanism insight was obtained from molecular dynamics simulations, suggesting that both the accessible pore volume of the MOFs and hydrogen-bonding interactions contribute to the strong periodic tendency of uranium(VI) extraction.