Dual-Emitting Mixed-Lanthanide Metal-Organic Framework for Ratiometric and Quantitative Visual Detection of 2,6-Pyridine Dicarboxylic Acid

The detection of the major biomarker of Bacillus anthracis, 2,6-dipicolinic acid (DPA), has attracted great interest in recent years. In this work, mixed-lanthanide metal-organic frameworks (M'LnMOFs), TbxEu1-x-cppa (cppa = 5-(5-carboxypyridin-3-yl)isophthalic acid), with different Tb/Eu ratios, were solvothermally synthesized. The results reveal that ratiometric fluorescent probe [Tb0.533Eu0.467-(Hcppa)1.5(H2O)(DMF)]·3H2O is water and acid-base stable and exhibits excellent sensitivity (LOD = 2.286 μM), high selectivity, and fast response (<2 min) for the detection of DPA. Due to the blocked energy transfer from Tb3+ to Eu3+ and the inner filter effect upon the addition of DPA, the fluorescent probe shows a distinct color change from orange-red to green. Furthermore, the visual detection of DPA was realized by identifying the RGB values of MOF-based agarose hydrogel films via a smartphone, highlighting the practical application of the fluorescent probe for DPA detection under aqueous solution conditions.

Metal-organic framework as a mimetic enzyme with excellent adaptability for sensitive chemiluminescence detection of glutathione in cell lysate

A novel [Co(L)(H₂O)₂] (1) was obtained by hydrothermal method and it exhibited a 1D chain with exposed carboxyl groups, the unique coordination mode made it have unusual physical and chemical stability. Meanwhile, 1 showed peroxidase-like and weak oxidase-like activity. 1 as a peroxidase mimic enzyme had an excellent affinity for the substrates luminol and H₂O₂. Compared with HRP, 1 had catalytic activity in a wide pH range and showed the best catalytic activity at pH 7.4. Meanwhile, the catalysis process of 1 was reversible and recyclable, and the catalytic activity remained stable after different pH and temperatures and long-time storage. Based on the inhibition of glutathione on luminol-H₂O₂-MOF 1 chemiluminescence signal, a chemiluminescence method for the determination of glutathione has been proposed with high sensitivity and selectivity and had been applied for detecting glutathione in cell lysate with satisfactory results.

A ratiometric fluorescent sensor made of a terbium coordination polymer for the anthrax biomarker 2,6-dipicolinic acid with on-site detection assisted by a smartphone app

Tb-NDBC is a quantitative ratiometric fluorescence sensor for DPA detection with high sensitivity and selectivity, a rapid response, and durability.

Luminescence switch based on the acid/base induced reversibility of covalent bonds in lanthanide(III) complexes

We report an exceptional example of Tb(III) luminescence switching using a reversible covalent bond. The antenna and quencher moieties attached to a ligand of a Tb(III) complex undergo acid/base-driven exchange based on the reversible formation of a hemiaminal ether structure to achieve on-off regulation of luminescence.

Anti-diabetic and anti-parasitic properties of a family of luminescent zinc coordination compounds based on the 7-amino-5-methyl-1,2,4-triazolo[1,5-a]pyrimidine ligand

We report on the formation of a triazolopyrimidine derivative ligand, 7-amino-5-methyl-1,2,4-triazolo[1,5-a]pyrimidine (7-amtp), and a new family of coordination compounds based on this ligand and zinc as metal ion, synthesized by conventional routes. These materials possess different mononuclear structures, namely [ZnCl₂(7-amtp)₂] (1), [Zn(7-amtp)₂(H₂O)₄](NO₃)₂·2(7-amtp)·6H₂O (2) and [Zn(7-amtp)₂(H₂O)₄](SO₄)·1.5H₂O (3) derived from the use of different zinc (II) salts, in such a way that the counterions govern the crystallization to a large extent. These compounds present and show variable luminescent properties based on ligand-centred charge transfers which have been deeply studied by Time Dependent Density Functional Theory (TD-DFT) calculations. When these compounds are transferred to solution, preserving complex entities as corroborated by NMR studies, they present interesting anti-diabetic and anti-parasitic capabilities, with a comparatively higher selectivity index than other previously reported triazolopyrimidine-based materials. The results derived from in vivo experiments conducted in mice also confirm their promising activity as anti-diabetic drug being capable of dropping glucose levels after oral administration. Therefore, these new materials may be considered as excellent candidates to be further investigated in the field of luminescent coordination compounds with biomedical applications.

A Luminescent Mg-Metal-Organic Framework for Sustained Release of 5-Fluorouracil: Appropriate Host-Guest Interaction and Satisfied Acid-Base Resistance

It is important to achieve a moderate sustained release rate for drug delivery, so it is critical to regulate the host-guest interactions for the rational design of a carrier. In this work, a nano-sized biocompatible metal-organic framework (MOF), Mg(H₂TBAPy)(H₂O)₃·C₄H₈O₂ (TDL-Mg), was constructed by employing π-conjugated 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H₄TBAPy) as a ligand and used for 5-fluorouracil (5-FU) loading (28.2 wt %) and sustained slow release. TDL-Mg exhibits a 3D supramolecular architecture featuring a 1D rectangle channel with a size of 6.2 × 8.1 Ų and a Brunauer-Emmett-Teller surface area of 627 m²·g^-1. Channel microenvironment analysis shows that the rigid H₂TBAPy^2- ligand adopts special torsion to stabilize the channels and offer rich π-binding sites; the partially deprotonated carboxyls not only participate in the formation of strong hydrogen bonds but also create a mild pH buffer environment for biological applications. Suitable host-guest interactions are generated by the synergistic effect of polydirectional hydrogen bonds, multiple π-interactions, and confined channels, which allow 5-FU@TDL-Mg to release 76% of load in 72 h, a medically reasonable rate. Microcalorimetry was used to directly quantify these host-guest interactions with a moderate enthalpy of 22.3 kJ·mol^-1, which provides a distinctive thermodynamic interpretation for understanding the relationship between the MOF design and the drug release rate. Additionally, the nano-sized 5-FU@TDL-Mg can be taken up by mouse breast cancer cells (4T1 cells) for imaging based on the dramatic fluorescence change during the release of 5-FU, exhibiting potential applications in biological systems.

A lanthanide–organic crystalline framework material encapsulating 1,3,6,8-tetrakis(p-benzoic acid)pyrene: selective sensing of Fe3+, Cr2O72−and colchicine and white-light emission

A facile strategy was used to construct a series of composite materials with color-tunable and white light emission by encapsulating 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H₄TBAPy) into framework material [Eu(MCTCA)_1.5(H₂O)₂]·1.75H₂O.

A Series of Lanthanide-Based Metal-Organic Frameworks Derived from Furan-2,5-dicarboxylate and Glutarate: Structure-Corroborated Density Functional Theory Study, Magnetocaloric Effect, Slow Relaxation of Magnetization, and Luminescent Properties

Herein, through a dual-ligand strategy, we report eight isorecticular lanthanide(III) furan-2,5-dicarboxylic acid metal-organic frameworks (Ln-MOFs) with the general formula {[Ln(2,5-FDA)_0.5(Glu)(H₂O)₂]· xH₂O} _n [Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6), Er (7), and Yb (8); 2,5-FDA^2- = furan-2,5-dicarboxylate and Glu^2- = glutarate; x = 0.5 for 1, 2, and 4 and x = 0 for 3 and 5-8], synthesized under solvothermal conditions by using an N, N'-dimethylformamide/H₂O mixed solvent system. Crystallographic data reveal that all eight Ln-MOFs 1-8 crystallize in the orthorhombic Pnma space group. All of the MOFs are isostructural as well as isomorphous with distorted monocapped square-antiprismatic geometry around the Ln1 metal center. In Ln-MOFs 1-8, the 2,5-FDA^2- and Glu^2- ligands exhibit μ₂-κ⁴,η¹:η¹:η¹:η¹ and μ₃-κ⁵,η²:η¹:η¹:η¹ coordination modes, respectively. Topologically, assembled Ln-MOFs 1-8 consist of the 2D cem topological type. The designed Ln-MOFs 1-8 are further explored for structure-corroborated density functional theory study. Meanwhile, room temperature photoluminescence properties of Ln-MOFs 2 and 4 and magnetic properties of Ln-MOFs 3 and 5 have been explored in detail. A highly intense, ligand-sensitized, Ln³⁺ f-f photoluminescence emission is exhibited by Ln-MOFs 2 [Eu³⁺ (red emission)] and 4 [Tb³⁺ (green emission)]. Magnetic studies suggest weak antiferro- and ferromagnetic interactions between adjacent Gd^III ions in Ln-MOF 3, thereby displaying a large magnetocaloric effect. The magnetic data measured at T = 2 K and Δ H = 30 kOe depict that the -Δ S_m value per unit mass reaches 32.1 J kg^-1 K^-1, which is larger than most of the Gd^III-based complexes reported. The alternating-current susceptibility measurements on Ln-MOF 5 revealed that out-of-phase signals are frequency- and temperature-dependent under both 0 and 2 kOe direct-current fields, thereby suggesting a typical slow magnetic relaxation behavior with two relaxation processes. This is further supported by the Cole-Cole plots at 2.4-6 K.

Ratiometric fluorescence determination of the anthrax biomarker 2,6-dipicolinic acid using a Eu3+/Tb3+-doped nickel coordination polymer

Tb³⁺_0.6/Eu³⁺_0.4@Ni-BTC is a quantitative ratiometric fluorescence sensor for DPA detection with high sensitivity, anti-interference, rapid response and durability.

2,5-Furandicarboxylic acid as a linker for lanthanide coordination polymers: the role of heteroaromatic π–π stacking and hydrogen bonding

Heteroaromatic carboxylate ligands are very intriguing components of coordination assemblies such as coordination polymers (CPs) due to their inherently multitopic structures.

Stable Lanthanide-Organic Framework Materials Constructed by a Triazolyl Carboxylate Ligand: Multifunction Detection and White Luminescence Tuning

Under hydrothermal conditions, we have successfully synthesized six isostructural lanthanide coordination polymers, [LnL_1.5(H₂O)₂]·1.75H₂O (1-6; Ln = Eu, La, Pr, Nd, Sm, Gd), by the reaction of 5-methyl-1-(4-carboxylphenyl)-1 H-1,2,3-triazole-4-carboxylic acid (H₂L) and Ln(NO₃)₃·6H₂O. Structural analysis shows that polymers 1-6 show novel three-dimensional supramolecular network structures. The luminescent properties for polymer 1 have been investigated at room temperature. The results have shown that polymer 1 can be used as a chemical sensor for multifunctional testing such as UO₂²⁺, Fe³⁺ ion detection, and small organic molecule detection because of its strong fluorescence properties. In particular, polymer 1 exhibits extremely high selectivity and sensitivity for the detection of Fe³⁺ ions. In addition, white-light emission is achieved through a reasonable tuning proportion by mixing Gd³⁺ and Eu³⁺.

Assembly of ZnII and CdII coordination polymers with different dimensionalities based on the semi-flexible 3-(1H-benzimidazol-2-yl)propanoic acid ligand

Two new coordination polymers, namely, poly[[μ3-3-(1H-benzimidazol-2-yl)propionato]zinc(II)], [Zn(C10H8N2O2)] n , (1), and poly[bis-[μ2-3-(1H-benzimid-azol-2-yl)propionato]cadmium(II)], [Cd(C10H8N2O2)2] n , (2) have been synthesized from 3-(1H-benzoimidazol-2-yl)propanoic acid ligands through a mixed-ligand synthetic strategy under a solvothermal environment, and studied by single-crystal X-ray diffraction. Complex 1 crystallizes in the ortho-rhom-bic space group Pbca and features a two-dimensional structure formed by a binuclear Zn2O4 core. Complex 2, however, crystallizes in the monoclinic space group P21/c and forms a one-dimensional chain structure. The ZnII and CdII ions have different coordination numbers and the 3-(1H-benzoimidazol-2-yl)propano-ate ligands display different coordination modes. The structures reported here show the importance of the selection of metal ions and suitable ligands.

A thermosensitive fluorescent Eu-based metal–organic framework and its polyether sulfone composite film as a thermal sensor

Thermosensitive fluorescent [Eu(NDC)(H₂O)Cl] (1) (H₂NDC = 2,6-Naphthalene dicarboxylic acid) was fabricated with polyether sulfone (PES) into composite films. 40% 1@PES film showed highly sensitive and repeatable thermal sensor properties in an alarm device.

Novel anti-diabetic and luminescent coordination compounds based on vanadium

Novel vanadium coordination compounds have been synthesized. Both compounds exhibit intense photoluminescence emission and showin vivoantidiabetic activity.

Lanthanide MOFs constructed based on a difunctional ligand with bimodal emission and Eu3+ doped Dy3+ materials: white emission and color tuning

A new strategy for multicolor materials by Dy and Eu cations.

Design and synthesis of luminescent porous coordination polymers for chromaticity modulation, sensing of nitrobenzene and iodine encapsulation

A family of porous coordination polymers constructed from C_2v symmetry ligands with increased conjugation moieties was systematically designed and prepared, which is highly promising for chromaticity modulation, sensing of nitrobenzene, and I₂ encapsulation.

Metal-organic frameworks for artificial photosynthesis and photocatalysis

Solar energy is an alternative, sustainable energy source for mankind. Finding a convenient way to convert sunlight energy into chemical energy is a key step towards realizing large-scale solar energy utilization. Owing to their structural regularity and synthetic tunability, metal-organic frameworks (MOFs) provide an interesting platform to hierarchically organize light-harvesting antennae and catalytic centers to achieve solar energy conversion. Such photo-driven catalytic processes not only play a critical role in the solar to chemical energy conversion scheme, but also provide a novel methodology for the synthesis of fine chemicals. In this review, we summarize the fundamental principles of energy transfer and photocatalysis and provide an overview of the latest progress in energy transfer, light-harvesting, photocatalytic proton and CO2 reduction, and water oxidation using MOFs. The applications of MOFs in organic photocatalysis and degradation of model organic pollutants are also discussed.

Metal-controlled structural variations of coordination architectures constructed from flexible 1H-benzimidazole-1-propionic acid

Five low-dimensional coordination polymers and a novel discrete dodecametallic cage have been obtained from appropriate transition metals in combination with a flexible bifunctional benzimidazole carboxylic acid.

Structurally simple complexes of CO2

A wide range of structurally characterized adducts of CO₂are discussed in this review, from the strongly bound, charge assisted carbamate complexes through the weaker halide and pseudo-halide complexes to the weakest possible inclusion complexes.

Structure variations of a series of lanthanide complexes constructed from quinoline carboxylate ligands: photoluminescent properties and PMMA matrix doping

A series of lanthanide complexes constructed from H₂qldc are synthesized and the luminescence properties discussed.

Architectures varying from discrete molecular units to 2-dimensional coordination polymers and photoluminescence behavior of zinc and cadmium comprising an anionic zwitterion of rigid 4,5-dicarboxy-1,3-dimethyl-1H-imidazolium iodide

A rigid ligand, 4,5-dicarboxy-1,3-dimethyl-1H-imidazolium iodide (H₂DDII) and crystallized as zwitterion (1) and employed in the synthesis of anionic zwitterion complexes or coordination polymers (CPs)2–6of Zn(ii) and Cd(ii).

Preparation, crystal structures and conformations of six complexes based on 1,4-bis(benzimidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene

Six manganese(ii), cobalt(ii), copper(ii) and cadmium(ii) complexes based on dibenzimidazolyl ligands with the 1,2,4,5-tetramethylbenzene linker have been prepared and characterized.

A highly sensitive mixed lanthanide metal-organic framework self-calibrated luminescent thermometer

A new mixed lanthanide metal-organic framework thermometer Tb0.9Eu0.1PIA with the significantly high sensitivity of 3.53% per K has been realized by making use of an organic ligand, 5-(pyridin-4-yl)isophthalate, with higher triplet state energy.