Lanthanide Organic Frameworks Research Articles

Lanthanide-organic frameworks based on terphenyl-tetracarboxylate ligands: syntheses, structures, optical properties and selective sensing of nitro explosives

Three isostructural three-dimensional (3D) lanthanide-based metal-organic frameworks [Ln2L(H2L)(NMP)2]·H2O (Ln=Sm ( 1 ), Eu ( 2 ), Gd ( 3 ); H4L=1,1′:4′,1″-terphenyl-2′,4,4″,5′-tetracarboxylic acid; NMP= N -methyl-2-pyrrolidone) have been synthesized and structurally characterized. In 1 – 3 , two Ln3+ ions are doubly-bridged by two oxygen atoms of two carboxylate groups to form the dinuclear Ln2(OCOO–)2 unit. Each Ln2(OCOO–)2 unit links with four H2L2− ligands and four L4− ligands to lead to the 3D framework, which can be rationalized as a new trinodal 4,4,8-connected (44.62)(45.6)(412.616) topological network by considering the dinuclear Ln2(OCOO–)2 units as 8-connected nodes and L4−/H2L2− ligands as planar 4-connected nodes, respectively. 1 and 3 exhibit blue emission originated from the ligand with the emission maximum at 384 nm, while 2 shows intense characteristic red emission of Eu3+ ions and weak ligand-centered emission. Moreover, 2 has fluorescent quenching response towards the aromatic nitro compounds, especially for the 3,4-dinitrotoluene (3,4-DNT) with the linear Stern-Volmer relationship in the concentration range of 0–1 mM and the quenching constant ( K sv) of 2.084×103 M−1.

Metal-Organic Frameworks with Tb4 Clusters as Nodes: Luminescent Detection of Chromium(VI) and Chemical Fixation of CO2.

Two multifunctional metal-organic frameworks based on cubane-like tetrahedron Tb4 clusters as nodes have been synthesized and characterized. Compound 1 exhibits a 2D lanthanide-organic framework with Tb4 clusters as nodes, and compound 2 possesses a 3D framework with Tb4 clusters and Mn2+ as nodes. Interestingly, luminescent investigations on them reveal that the two compounds can act as recyclable luminescent probes for chromium(VI) anion species and the corresponding detection limit can reach 10-7 mol/L. Furthermore, 1 and 2 own efficient catalytic activity for the chemical fixation of CO2 with epoxides under mild conditions. Importantly, they both can be recycled at least three times without compromising the activity.

Lanthanide organic frameworks for luminescence sensing of nitrobenzene and nitrophenol with high selectivity

A series of lanthanide(III)–organic frameworks, namely {[Ln2(L)3(H2O)4]·10H2O}n (Sm 1, Eu 2, Gd 3, Tb 4, Dy 5 and Ho 6, H2L = 5-(pyridine-4-ylmethoxy)isophthalic acid) have been synthesized under solvothermal conditions. Compounds 1–6 are isostructural and exhibit an interesting 3D pcu topology with binuclear [Ln2(CO2)6] units as 6-connected nodes, and free water molecules are filled in 3D coordination frameworks through hydrogen-bonding interactions. Compound 4 can be used as a fluorescent probe for sensing nitroaromatic compounds with high sensitivity and selectivity based on luminescence quenching effects arising from host−guest interactions in DMF system. In particular, compound 4 can sense nitrobenzene (NB) and nitrophenol isomers (2-, 3- and 4-NP) simultaneously. Thus, this material can be potentially used as a luminescent sensor for nitroaromatic compounds.

Improving the quantum efficiency of the lanthanide-organic framework [Eu2(MELL)(H2O)6] by heating: A simple strategy to produce efficient luminescent devices

Luminescent materials have been widely studied due to the increasing number of applications in catalysis, biosensors and electro-optical devices. In this sense, the improvement of luminescent efficiency has been sought and several strategies have been proposed. In this work, experimental and theoretical approaches were used to achieve and understand the improvement of luminescent efficiency of lanthanide organic frameworks through a heating process. In this study, [Eu2(MELL)(H2O)6] (EuMELL) was synthesized and characterized by scanning electron and fluorescence microscopies, thermogravimetric analysis, powder X-ray diffraction and photoluminescence techniques. In parallel, theoretical simulations of the material in solid phase were carried out using semiempirical approaches. The comparison between experimental and theoretical results indicated that the more accurate structure was calculated using the Sparkle/PM3 model. The temperature effects on the structure as well as the photophysical properties were evaluated by measurements in situ heating and compared to theoretical simulations using the Sparkle/PM3 geometry. The excellent agreement between the computational and experimental results in this study opens up a series of possibilities for studying other systems, particularly when structural details are not easily available. Moreover, that the controlled heating contributes to improve its the quantum efficiency by approximately 45%, suggesting that this approach can be a valuable tool for technological applications.

Phosphonate MOFs Composite as Off-On Fluorescent Sensor for Detecting Purine Metabolite Uric Acid and Diagnosing Hyperuricuria.

The recent discovery of lanthanide organic frameworks (Ln-MOFs) offers the potential for biomarkers or metabolites sensing. This is another field that is closely connected with life science and medicine. In this work, a stable and luminescent phosphonate Ln-MOFs MIL-91(Al:Eu) and its derivatives composite Cu2+@MIL-91(Al:Eu) were synthesized. The rebound of luminescence of Cu2+@MIL-91(Al:Eu) that origin of Eu3+ is observed in the presence of uric acid. This On-Off-On pattern is utilized for detecting uric acid, which is the final metabolite of purine. The composite reveals excellent selectivity and sensitivity for sensing uric acid. The detection of uric acid in real urine is also investigated. The effective detection of uric acid and tentative diagnosis of hyperuricuria on the basis of test paper is demonstrated.

Photoluminescence and Hydrothermal Stability Correlations via Isoreticular/Structural fcu Rare-Earth Organic Frameworks Platform

Because of the discovery of a high-symmetry rare-earth hexanuclear secondary building unit, controllable design and assembly of rare-earth organic frameworks (REOFs) have become feasible. Subsequently, series of isoreticular/structural fcu REOFs platform was herein successfully produced by solvothermal reactions and reticular chemistry. After the crystal structural information and permanent porosity were confirmed, thorough investigations toward photoluminescence and hydrothermal stability were implemented. As a result, distinct and interesting luminescence behavior is observed among the series of REOFs. 1-Dy and 2-Dy mainly display ligand-centered emission, while 1-Eu and 2-Eu are predominated by metal-centered emission. More interestingly, 1-Eu reveals excitation dependent luminescence, generating the first example of a white light emission phosphor in single phase fabricated from a sole Eu3+ ion and sole organic linker. 2-Eu however does not exhibit such features and stays mostly unchanged upon the var...

Photoluminescent and Slow Magnetic Relaxation Studies on Lanthanide(III)-2,5-pyrazinedicarboxylate Frameworks.

In the series described in this work, the hydrothermal synthesis led to oxidation of the 5-methyl-pyrazinecarboxylate anion to the 2,5-pyrazinedicarboxylate dianion (2,5-pzdc) allowing the preparation of three-dimensional (3D) lanthanide(III) organic frameworks of formula {[Ln2(2,5-pzdc)3(H2O)4]·6H2O}n [Ln = Ce (1), Pr (2), Nd (3), and Eu (4)] and {[Er2(2,5-pzdc)3(H2O)4]·5H2O}n (5). Single-crystal X-ray diffraction on 1-5 reveals that they crystallize in the triclinic system, P1̅ space group with the series 1-4 being isostructural. The crystal structure of the five compounds are 3D with the lanthanide(III) ions linked through 2,5-pzdc2- dianions acting as two- and fourfold connectors, building a binodal 4,4-connected (4·648)(426282)-mog network. The photophysical properties of the Nd(III) (3) and Eu(III) (4) complexes exhibit sensitized photoluminescence in the near-infrared and visible regions, respectively. The photoluminescence intensity and lifetime of 4 were very sensitive due to the luminescence quenching of the 5D0 level by O-H oscillators of four water molecules in the first coordination sphere leading to a quantum efficiency of 11%. Variable-temperature magnetic susceptibility measurements for 1-5 reveal behaviors as expected for the ground terms of the magnetically isolated rare-earth ions [2F5/2, 2H4, 4I9/2, 7F0, and 4I15/2 for Ce(III), Pr(III), Nd(III), Eu(III), and Er(III), respectively] with MJ = 0 (2 and 4) and ±1/2 (1, 3, and 5). Q-band electron paramagnetic resonance measurements at low temperature corroborate these facts. Frequency-dependent alternating-current magnetic susceptibility signals under external direct-current fields in the range of 100-2500 G were observed for the Kramers ions of 1, 3, and 5, indicating slow magnetic relaxation (single-ion magnet) behavior. In these compounds, τ-1 decreases with decreasing temperature at any magnetic field, but no Arrhenius law can simulate such a dependence in all the temperature range. This dependence can be reproduced by the contributions of direct and Raman processes, the Raman exponent (n) reaching the expected value (n = 9) for a Kramers system.

Hydrophilic microporous lanthanide-organic frameworks based on 4,4′-biphenyldiacetate: Synthesis, crystal structures and sorption properties

Fifteen microporous coordination polymers of symmetrical and flexible 4,4′-biphenyldiacetate (bpda2–) with lanthanide(III) cations (Ln3+) of formula {[Ln2(bpda)3(H2O)]⋅2H2O}n (Ln=La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Ho (10), Er (11), Tm (12), Yb (13), Lu (14), Y (15)), have been synthesized and characterized. Single crystal X-ray diffraction (for 1, 3 and 4) in combination with powder X-ray diffraction showed isostructural compounds with an infinite secondary building unit (SBU). In this SBU, two crystallographically independent lanthanide ions are connected by three carboxylate groups in chelating-bridging mode to zig-zag Ln-carboxylate chains. These chains are assembled by the biphenyl part of the ligand to a 3D network with water molecules in channels with rectangular cross-sections of ∼1.6×3Å2. Thermogravimetric analysis indicates complete removal of the water molecules at 150°C and thermal stability up to 380°C. Stability studies on compound 1 show no degeneration in crystallinity after refluxing in water or different organic solvents. The dehydrated compound 1 exhibited no N2 or H2 uptake at 77K and no CH4 or CO2 uptake at 273K up to 1bar. High-pressure (17bar, 273K) CO2 uptake of dehydrated [Ln2(bpda)3]n corresponded to the formation of {[Ln2(bpda)3]·CO2}n with about 40% of the adsorbed CO2 retained upon desorption. Water vapor sorption of activated and hygroscopic [Ln2(bpda)3]n reformed {[Ln2(bpda)3(H2O)]·2H2O}n. 4,4′-Biphenyldiacetic acid (H2bpda) shows blue emission, its europium 6 and terbium 8 compounds show red and weak green luminescence under UV light irradiation, with the bpda2− ligand acting as an antenna ligand for the europium(III) ions.

A novel naphthalenediimide-based lanthanide-organic framework with polyoxometalate templates exhibiting reversible photochromism.

The first visible-light-responsive photochromic polyoxometalate-templated lanthanide-organic framework (LOF) has been constructed from a carboxyphenyl-substituted naphthalenediimide (NDI) derivative, which displays an unusual four-fold interpenetration of an srs topological network, featuring a variety of anion-π interactions between polyoxoanions and π-acidic NDI moieties, and undergoes a rapid reversible photochromic transformation upon blue light irradiation.

Two 3D nonlinear optical and luminescent lanthanide-organic frameworks with multidirectional helical intersecting channels

Two chiral 3D lanthanide-organic frameworks with multidirectional helical intersecting channels, [Ln(Hpzc)(Hida)]n were hydrothermally synthesized and characterized.

Synthesis, structure, characterization, and multifunctional properties of a family of rare earth organic frameworks

A series of isomorphic 3D layered rare earth hydroxide (LREH) frameworks RE3(OH)7(1,5-NDS) (RE = Y (1), Gd (2), Er (3), Yb (4); 1,5-NDS = 1,5-naphthalenedisulfonate) has been synthesized under hydrothermal conditions. The crystal structures, thermal stabilities, photoluminescence, and magnetic properties of these compounds have been investigated. The results demonstrate that the compounds are highly stable even at 351 °C and emit strong purple fluorescence, whose colour can be tuned by the coordinated rare earth ions. Their magnetic susceptibilities have also been measured, leading the compounds to be promising multifunctional materials.

NIR emission and luminescent sensing of a lanthanide-organic framework with Lewis basic imidazole and pyridyl sites.

A series of lanthanide-organic frameworks [Ln(Himdc)(ina)(H2O)]n (Ln = Eu 1a; Sm 1b; and Nd 1c, H3imdc = imidazole-4,5-dicarboxylic acid, Hina = isonicotinic acid) were synthesized under hydrothermal conditions. All compounds 1a-1c consist of a 3D microporous lanthanide carboxylate ([Eu(COO)3]n) framework and uncoordinated Lewis basic pyridyl and imidazole groups hung in the channels. The luminescence investigations show that the compound 1c displays an interesting NIR luminescence property. The compound 1a exhibits a good potential as a luminescent multi-responsive sensing material for Fe3+ ions and Cr2O72- anions.

A fluorescent lanthanide-organic framework for highly sensitive detection of nitroaromatic explosives

A lanthanide-organic framework constructed from a new π-electron rich ligand 5,5′-(9H-carbazole-3,6-diyl)diisophthalic acid (H4L) and Tb(NO3)3·6H2O, namely, [(CH3)2NH2][TbL] (1), has been synthesized under solvothermal condition. X-ray diffraction analysis reveals that complex 1 exhibits a 3D porous framework featuring a (4,8)-connected sqc net. The solid sample of 1 exhibits strong green fluorescence in the visible region upon excitation at 354nm. The fine grinding particles of 1 dispersed in ethanol shows good sensitivity for picric acid (PA), which can be reused at least five times for detecting PA. The good sensitivity and recyclability of 1 make it a potential fluorescent sensor for explosives detection.

Multifunctional Luminescent Eu(III)-Based Metal-Organic Framework for Sensing Methanol and Detection and Adsorption of Fe(III) Ions in Aqueous Solution.

A novel lanthanide-organic framework (Eu-HODA), consisting of 2,2',3,3'-oxidiphthalic acids as efficient sensitizing units, is assembled and characterized. Eu-HODA features rare chiral helical channels despite the achiral nature of H4ODA. It is found that this MOF shows a unique luminescent response to methanol, in contrast to n-propanol and ethanol. Eu-HODA reveals a turn-off luminescence switching initiated by acetone molecules with an EC50 of 0.03 vol %, which is below the occupational exposure limit of acetone stipulated by the American Conference of Governmental Industrial Hygienists. Furthermore, it also exhibits high sensitivity (Stern-Volmer constant KSV = 2.09 × 104 L/mol) and low detection limit (6.4 ppb) for Fe3+ ions in pure water because of the existence of uncoordinated carboxyl groups within open frameworks. Eu-HODA-based test paper provides a simple and reliable detection method for Fe3+ in practical applications.

Visible‐Light Excited Luminescent Thermometer Based on Single Lanthanide Organic Frameworks

Isostructural lanthanide organic frameworks (Me2NH2)3[Ln3(FDC)4(NO3)4]·4H2O (Ln = Eu (1), Gd (2), Tb (3), H2FDC = 9‐fluorenone‐2,7‐dicarboxylic acid), synthesized under solvothermal conditions, feature a Ln‐O‐C rod‐packing 3D framework. Time‐resolved luminescence studies show that in 1 the energy difference between the H2FDC triplet excited state (17794 cm−1) and the 5D0 Eu3+ level (17241 cm−1) is small enough to allow a strong thermally activated ion‐to‐ligand back energy transfer. Whereas the emission of the ligand is essentially constant the 5D0→7F2 intensity is quenched when the temperature increases from 12 to 320 K, rendering 1 the first single‐lanthanide organic framework ratiometric luminescent thermometer based on ion‐to‐ligand back energy transfer. More importantly, this material is also the first example of a metal organic framework thermometer operative over a wide temperature range including the physiological (12‐320 K), upon excitation with visible light (450 nm).

A Bifunctional Europium-Organic Framework with Chemical Fixation of CO2 and Luminescent Detection of Al3.

A novel three-dimensional lanthanide-organic framework {[Eu(BTB)(phen)]·4.5DMF·2H2O}n (1) has been synthesized. Structural characterization suggests that framework 1 possesses one-dimensional channels with potential pore volume, and the large channels in the framework can capture CO2. Interestingly, investigations on the cycloaddition reaction of CO2 and epoxides reveal that compound 1 can be considered as an efficient catalyst for CO2 fixation with epoxides under 1 atm pressure. Importantly, 1 can be reused at least five times without any obvious loss in catalytic activity. Furthermore, the luminescent explorations of 1 reveal that 1 can act as a recyclable sensor of Al3+, and the corresponding detection limit can reach 5 × 10-8 M (1.35 ppb), which is obviously lower than the United States Environmental Protection Agency's recommended level of Al3+ in drinking water (200 ppb). These results show that 1 has a level of sensitivity higher than that of other reported MOF-based sensors of Al3+.

The Uncommon Channel-Based Ln-MOFs for Highly Selective Fe3+ Detection and Superior Rhodamine B Adsorption.

Two new isostructural 3D lanthanide-organic frameworks [H2 N(Me)2 ] [Ln3 (OH)(bpt)3 (H2 O)3 ] (DMF)2 ⋅(H2 O)4 (1-Ln; Ln=Sm and Eu) with a 1D channel (25 Å) have been successfully assembled from the rare trinuclear [Ln3 (OH)(COO)9 ] clusters and biphenyl-3,4',5-tricarboxylic acid (H3 bpt) and exhibit high stability towards water in the pH range 3-10. MOF 1-Eu is a promising luminescent probe for sensing Fe3+ in aqueous solution and is also selective towards rhodamine B (RhB) with a superior adsorption capacity of 735 mg g-1 , which is the highest among the reported Ln-MOFs for RhB removal so far. Periodic DFT calculations further confirmed the selective adsorption of rhodamine B over other dyes.

Lanthanide Chemistry: From Coordination in Chemical Complexes Shaping Our Technology to Coordination in Enzymes Shaping Bacterial Metabolism

Lanthanide chemistry has only been extensively studied for the last 2 decades, when it was recognized that these elements have unusual chemical characteristics including fluorescent and potent magnetic properties because of their unique 4f electrons.1,2 Chemists are rapidly and efficiently integrating lanthanides into numerous compounds and materials for sophisticated applications. In fact, lanthanides are often referred to as "the seeds of technology" because they are essential for many technological devices including smartphones, computers, solar cells, batteries, wind turbines, lasers, and optical glasses.3-6 However, the effect of lanthanides on biological systems has been understudied. Although displacement of Ca2+ by lanthanides in tissues and enzymes has long been observed,7 only a few recent studies suggest a biological role for lanthanides based on their stimulatory properties toward some plants and bacteria.8,9 Also, it was not until 2011 that the first biochemical evidence for lanthanides as inherent metals in bacterial enzymes was published.10 This forum provides an overview of the classical and current aspects of lanthanide coordination chemistry employed in the development of technology along with the biological role of lanthanides in alcohol oxidation. The construction of lanthanide-organic frameworks will be described. Examples of how the luminescence field is rapidly evolving as more information about lanthanide-metal emissions is obtained will be highlighted, including biological imaging and telecommunications.11 Recent breakthroughs and observations from different exciting areas linked to the coordination chemistry of lanthanides that will be mentioned in this forum include the synthesis of (i) macrocyclic ligands, (ii) antenna molecules, (iii) coordination polymers, particularly nanoparticles, (iv) hybrid materials, and (v) lanthanide fuel cells. Further, the role of lanthanides in bacterial metabolism will be discussed, highlighting the discovery that lanthanides are cofactors in biology, particularly in the enzymatic oxidation of alcohols. Finally, new and developing chemical and biological lanthanide mining and recycling extraction processes will be introduced.

Lanthanide-Organic Frameworks (LnOFs) Containing 1D Metal/Oxygen Ribbons with Cubane-like and Triangle Motifs: Synthesis, Structure, Luminescence and Slow Magnetic Relaxation

Four lanthanide-based three-dimensional(3D) complexes {[Ln5(μ2-O)(μ3-OH)5(TCA)2(NO3)(CH3COO)(H2O)2]⋅NH(CH3)2⋅DMA⋅(H2O)3}n (H3TCA=4,4′,4′′-tricarboxytriphenylamine; DMA=N,N-dimethylacetamide; Ln=Dy(1), Y(2)) and {[Ln2(μ2-OH)(μ3-OH)2(TCA)(H2O)]⋅DMA⋅H2O}n (Ln=Er(3), Yb(4)) have been hydrothermally synthesized based on a flexible tricarboxylate ligand H3TCA. Single-crystal X-ray diffraction studies reveal that complexes 1–4 exhibit a 3D framework constructed through well-isolated one-dimensional(1D) metal/oxygen ribbons. Therein, the unusual pentanuclear unit comprised of cubane-like [Ln4O4] cluster and the additional Ln (III) center can be observed in complexes 1 and 2, while lanthanide triangle motifs appear in complexes 3 and 4. Static and dynamic magnetic measurements of 1 and 3 have been performed. Both complexes reveal frequency dependence of the out-of-phase signals, suggesting the slow magnetic relaxation behavior for 1 and 3. 3 and 4 exhibit characteristic emissions of the corresponding Er3+ and Yb3+ ions in the NIR region, respectively.

Solvent- and metal-directed lanthanide-organic frameworks based on pamoic acid: observation of slow magnetization relaxation, magnetocaloric effect and luminescent sensing

Two types of lanthanide coordination polymers, namely, [Ln(PA)(NO3)(DMA)3] n (Ln=Gd (1), Dy (2), Eu (3), Tb (4)) (type I), and {[Ln2(PA)3(DMF)4]·2DMF} (Ln=Eu (5), Tb (6)) (type II) (PA=Pamoic acid, DMA=dimethylacetamide, DMF=N,N-dimethylformamide), have been synthesized by the reaction of Ln(NO3)3·6H2O with pamoic acid through layer diffusion method. These complexes were characterized by single crystal X-ray diffraction, infrared spectroscopy (IR), thermogravimetric analysis (TGA), fluorescence and magnetic measurements. Solvents and lanthanide atoms in the reaction play an important role in controlling different structures. Type I demonstrated 1-D linear chain structure connected by Ln atoms and PA ligands. Type II exhibited non-interpenetrating 3-D 6-connected 43612 nets based on binuclear [Ln2(CO2)6(DMF)4] cores. Magnetic properties of complexes 1–4 were investigated in details. Complex 1 shows significant magnetocaloric effect with–ΔSm=20.37 J kg–1 K–1 at 3.0 K and 7 T. Complex 2 exhibits slow relaxation of the magnetization. Complexes 3–6 exhibit both ligand- and metal-centered fluorescent properties. Complex 6 demonstrates fluorescent sensing of DMF and Cu2+ ion.