A Multifunctional Dysprosium-Carboxylato 2D Metall-Organic Framework

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.

Challenges for exploiting nanomagnet properties on surfaces

Molecular complexes with single-molecule magnet (SMM) or qubit properties, commonly called molecular nanomagnets, are great candidates for information storage or quantum information processing technologies. However, the implementation of molecular nanomagnets in devices for the above-mentioned applications requires controlled surface deposition and addressing the nanomagnets' properties on the surface. This Perspectives paper gives a brief overview of molecular properties on a surface relevant for magnetic molecules and how they are affected when the molecules interact with a surface; then, we focus on systems of increasing complexity, where the relevant SMMs and qubit properties have been observed for the molecules deposited on surfaces; finally, future perspectives, including possible ways of overcoming the problems encountered so far are discussed.

Recent advances in metal-organic frameworks: Synthesis, application and toxicity

Metal-organic frameworks (MOFs) are a new class of crystalline porous hybrid materials with high porosity, large specific surface area and adjustable channel structure and biocompatibility, which are being investigated with increasing interest for energy storage and conversion, gas adsorption/separation, catalysis, sensing and biomedicine. However, the practical applications of MOFs make them release into the environment inevitable, posing a threat to humans and organisms. In this article, we cover advances in the currently available MOFs synthesis methods and the emerging applications of MOFs, especially in the biomedical field (therapeutic agents and bioimaging). Additionally, after evaluating the current status of main exposure routes and affecting factors in the field of MOFs-toxicity, the molecular mechanism is also clarified and identified. Knowledge gaps are identified from such a summarization and frontier development are explored for MOFs. Afterwards, we also present the limitations, challenges, and future perspectives in the study of the entire life cycle of MOFs. This review emphasizes the need for a more targeted discussion of the latest, widely used and effective versatile material class in order to exploit the full potential of high-performance and non-toxicity MOFs in the future.

Turn-off luminescence sensing, white light emission and magnetic studies of two-dimensional lanthanide MOFs

The lanthanide metal organic framework compounds [Ln(BPTA)1.5(Bpy)]·0.5DMF (Ln = Y, Eu, Gd, Tb, Dy; 1a-5a) and [Ln(BPTA)1.5(Phen)]·0.5DMF (Ln = Y, Eu, Gd, Tb, Dy; 1b-5b) were prepared by employing 2,5-bis(prop-2-yn-1-yloxy)terephthalic acid (2,5-BPTA) as the primary ligand and 2,2'-bipyridine (1a-5a) and 1,10-phenanthroline (1b-5b) as the secondary ligands. Single-crystal structural studies on [Gd(BPTA)1.5(Bpy)]·0.5DMF (3a) and [Dy(BPTA)1.5(Phen)]·0.5DMF (5b) indicated that the compounds have a two-dimensional structure. The Y compound exhibits blue emission, and the other compounds exhibit emission in the expected regions (λex = 350 nm). White light emission was achieved by careful mixing of the red (Eu3+) and green (Tb3+) components in the blue emitting Y compound. Thus, Y0.96Tb0.02Eu0.02 (bpy) and Y0.939Tb0.06Eu0.001 (phen) were found to show white emission when excited using a wavelength of 350 nm. The introduction of N-N-containing ancillary ligands (i.e., bpy and phen) increased the overall quantum yield (QY) of white light emission to 31% and 43%, respectively. The high QY observed for the Tb and Eu compounds was found to be sensitive and selective for the fluorometric detection of azinphos-methyl pesticide and trinitrophenol (TNP) in an aqueous medium at the ppb level. The same behaviour was observed when utilising the compounds as onsite paper strip sensors. Their magnetic properties were also studied, revealing for the Tb and Dy derivatives slow relaxation of the magnetisation at low temperature. The present study highlights the usefulness of rigid π-conjugated molecules such as 2,2'-bipyridine and 1,10-phenanthroline in enhancing the many utilities of rare-earth-containing MOFs towards white light emission, the sensing of harmful and dangerous substances and magnetic properties.

First Ultrathin Pure Polyoxometalate 2D Material as a Peroxidase-Mimicking Catalyst for Detecting Oxidative Stress Biomarkers

Although two-dimensional (2D) materials with ultrathin geometry and extraordinary electrical attributes have attracted substantial concern, exploiting new-type 2D materials is still a great challenge. In this work, an unprecedented single-layer pure polyoxometalate (POM) 2D material (2D-1) was prepared by ultrasonically exfoliating a one-dimensional (1D)-chain heterometallic crystalline germanotungstate Na₄[Ho(H₂O)₆]₂[Fe₄(H₂O)₂(pic)₆Ge₂W₂₀O₇₂]·16H₂O (1) (Hpic = picolinic acid). The 1D polymeric chain of 1 is assembled from particular {Ge₂W₂₀}-based [Fe₄(H₂O)₂(pic)₆Ge₂W₂₀O₇₂]^10- segments through bridging [Ho(H₂O)₆]³⁺ cations. 2D-1 is formed by π-π interaction driving force among adjacent 1D polymeric chains of 1. Also, the peroxidase-mimicking properties of 2D-1 toward detecting H₂O₂ were evaluated and good detection result was observed with a limit of detection (LOD) of 58 nM. Density functional theory (DFT) calculation further confirms that 2D-1 displays outstanding catalytic activity and active sites are located on Fe centers and Hpic ligands. Under the catalysis of uricase, uric acid can be transformed to allantoin and H₂O₂, and then, H₂O₂ oxidizes TMB to its blue ox-TMB in the presence of 2D-1 as a catalyst. Then, we utilized this cascade reaction to detect uric acid, which also exhibits prominent results. This research opens a door to prepare ultrathin pure POM 2D materials and broadens the scope of potential applications of POMs in biology and iatrology.

A New Microporous Lanthanide Metal-Organic Framework with a Wide Range of pH Linear Response

Lanthanide metal-organic frameworks (Ln-MOFs) have attracted extensive attention because of their structural adjustability and wide optical function applications. However, MOFs with a wide linear pH response and stable framework structures in acidic or alkaline solutions are rare to date. Here, we used 4,4',4″-s-triazine-2,4,6-triyltribenzoate (H₃TATB) as an organic ligand, coordinated with lanthanide ions (Eu³⁺/Tb³⁺), and synthesized a new metal-organic framework material. The material has a porous three-dimensional square framework structure and emits bright red or green fluorescence under 365 nm UV light. The carboxyl group of the ligand is prone to protonation in an acidic environment, and negatively charged OH^- and ligand (TATB^3-) have a competitive effect in an alkaline environment, which could affect the coordination ability of ligand. The luminescence degree of the framework decreases with the increase in the degree of acid and base. In particular, such fluorescence changes have a wide linear response (pH = 0-14), which can be used as a potential fluorescence sensing material for pH detection.

Metal-Organic Frameworks and Their Composites for Environmental Applications

From the point of view of the ecological environment, contaminants such as heavy metal ions or toxic gases have caused harmful impacts on the environment and human health, and overcoming these adverse effects remains a serious and important task. Very recent, highly crystalline porous metal-organic frameworks (MOFs), with tailorable chemistry and excellent chemical stability, have shown promising properties in the field of removing various hazardous pollutants. This review concentrates on the recent progress of MOFs and MOF-based materials and their exploit in environmental applications, mainly including water treatment and gas storage and separation. Finally, challenges and trends of MOFs and MOF-based materials for future developments are discussed and explored.

Two-dimensional dysprosium(III) coordination polymer: Structure, single-molecule magnetic behavior, proton conduction, and luminescence

A new dysprosium (III) coordination polymer [Dy(Hm-dobdc) (H₂O)₂]·H₂O (Dy-CP), was hydrothermal synthesized based on 4,6-dioxido-1,3-benzenedicarboxylate (H₄m-dobdc) ligand containing carboxyl and phenolic hydroxyl groups. The Dy(III) center adopts an octa-coordinated [DyO₈] geometry, which can be described as a twisted square antiprism (D_4d symmetry). Neighboring Dy(III) ions are interconnected by deprotonated Hm-dobdc³⁻ ligand to form the two-dimensional infinite layers, which are further linked to generate three-dimensional structure through abundant hydrogen bonds mediated primarily by coordinated and lattice H₂O molecules. Magnetic studies demonstrates that Dy-CP shows the field-induced slow relaxation of magnetization and the energy barrier U_eff/k_B and relaxation time τ₀ are 35.3 K and 1.31 × 10^–6 s, respectively. Following the vehicular mechanism, Dy-CP displays proton conductivity with σ equal to 7.77 × 10^–8 S cm⁻¹ at 353 K and 30%RH. Moreover, luminescence spectra reveal that H₄m-dobdc can sensitize characteristic luminescence of Dy(III) ion. Herein, good magnetism, proton conduction, and luminescence are simultaneously achieved, and thus, Dy-CP is a potential multifunctional coordination polymer material.

Layered Uranyl Phosphonates Encapsulating Co(II)/Mn(II)/Zn(II) Ions: Exfoliation into Nanosheets and Its Impact on Magnetic and Luminescent Properties

Layered heterometallic 5f-3d uranyl phosphonates can exhibit unique luminescent and/or magnetic properties, but the fabrication and properties of their 2D counterparts have not been investigated. Herein we report three heterobimetallic uranyl phosphonates, namely, [(UO₂ )₃ M(2-pmbH)₄ (H₂ O)₄ ] ⋅ 2H₂ O [MU, M=Co(II), CoU; Mn(II), MnU; Zn(II), ZnU; 2-pmbH₃ =2-(phosphonomethyl)benzoic acid]. They are isostructural and display two-dimensional layered structures where the M(II) centers are encapsulated inside the windows generated by the diamagnetic uranyl phosphonate layer. Each M(II) has an octahedral geometry filled with four water molecules in the equatorial positions and two phosphonate oxygen atoms in the axial positions. The uranium atoms adopt UO₇ pentagonal bipyramidal and UO₆ square bipyramidal geometries. The lattice and coordination water molecules can be released by thermal treatment and reabsorbed in a reversible manner, accompanied with changes of magnetic dynamics. Interestingly, the bulk samples of MU can be exfoliated in acetone via freezing and thawing processes forming nanosheets with single-layer or two-layer thickness (MU-ns). Magnetic studies revealed that the CoU and MnU systems exhibited field-induced slow magnetization relaxation at low temperature. Compared with crystalline CoU, the magnetic relaxation of the CoU-ns aggregates is significantly accelerated. Moreover, photoluminescence measured at 77 K showed slight red-shift of the five characteristic uranyl emission bands for ZnU-ns in comparison with those of the crystalline ZnU. This work gives the first examples of 2D materials based on 5f-3d heterometallic uranyl phosphonates and illustrates the impact of dimension reduction on their magnetic/optical properties.

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.

Dysprosium(III) Metal-Organic Framework Demonstrating Ratiometric Luminescent Detection of pH, Magnetism, and Proton Conduction

A multifunctional metal-organic framework, (Hdmbpy)[Dy(H₂dobdc)₂(H₂O)]·3H₂O (Dy-MOF, H₄dobdc = 2,5-dihydroxyterephthalic acid, dmbpy = 4,4'-dimethyl-2,2'-bipyridine), was synthesized and structurally characterized. The metal center Dy^III is connected by four carboxyl groups to form the [Dy₂(CO₂)₄] binuclear nodes, which are further interconnected by eight separate H₂dobdc^2- ligands to form a three-dimensional (3D) framework including hydrophilic triangular channels and abundant hydrogen-bonding networks. Dy-MOF has good stability in aqueous solution as well as in harsh acidic or alkaline solutions (pH range: 2.0-12.0). Furthermore, the luminescence signal of Dy-MOF undergoes a visualized color change as the acidity of the solution alters, which is the typical behavior of pH ratiometric probe. At a 100% relative humidity, Dy-MOF exhibits a high proton conductivity σ (1.70 × 10^-4 S cm^-1 at 303 K; 1.20 × 10^-3 S cm^-1 at 343 K) based on the proton hopping mechanism, which can be classified as a superionic conductor with σ exceeding 10^-4 S cm^-1. Additionally, the ferromagnetic interaction and magnetic relaxation behavior are simultaneously achieved in Dy-MOF. Herein, the combination of luminescence sensing, magnetism, and proton conduction in a single-phase 3D MOF may offer great potential applications in smart multitasking devices.

Photo-Induced Magnetic Hysteresis in a Cyanide-bridged Two-dimensional [Mn2W] Coordination Polymer

2D magnetic materials have been opening a new horizon in materials science. It is challenging to switch the magnetic hysteresis of 2D magnetic materials via light irradiation, applicable for future...

Multifunctional lanthanide MOF luminescent sensor built by structural designing and energy level regulation of a ligand

In order to reduce usage cost and simplify the detection process, it is necessary to develop multifunctional and multi-emitter Ln-MOF luminescent sensors.

Luminescent and Magnetic Tb-MOF Flakes Deposited on Silicon

The synthesis of a terbium-based 2D metal–organic framework (MOF), of formula [Tb(MeCOO)(PhCOO)₂] (1), a crystalline material formed by neutral nanosheets held together by Van der Waals interactions, is presented. The material can be easily exfoliated by sonication and deposited onto different substrates. Uniform distributions of Tb-2D MOF flakes onto silicon were obtained by spin-coating. We report the luminescent and magnetic properties of the deposited flakes compared with those of the bulk. Complex 1 is luminescent in the visible and has a sizeable quantum yield of QY = 61% upon excitation at 280 nm. Photoluminescence measurements performed using a micro-Raman set up allowed us to characterize the luminescent spectra of individual flakes on silicon. Magnetization measurements of flakes-on-silicon with the applied magnetic field in-plane and out-of-plane display anisotropy. Ac susceptibility measurements show that 1 in bulk exhibits field-induced slow relaxation of the magnetization through two relaxation paths and the slowest one, with a relaxation time of τ_lf ≈ 0.5 s, is assigned to a direct process mechanism. The reported exfoliation of lanthanide 2D-MOFs onto substrates is an attractive approach for the development of multifunctional materials and devices for different applications.