Lanthanide-based Coordination Polymers Research Articles

Solvothermal self-assembly of seven lanthanide(III) coordination polymers using diphenic acid and 1,10-phenanthroline as co-ligands: Efficient detection of picric acid and Cu2+ ions in aqueous medium by europium based coordination polymer

Lanthanide based coordination polymers (Ln-CPs) act as efficient chemo-sensors on interaction with the target analyte and show a detectable variation in their optical properties. This work demonstrates interaction of metal ions and nitroaromatic compounds with Eu based CP resulting in quenching of luminescence emission intensity. Approaching towards this aim, seven iso-structural lanthanide coordination polymers having the formulae, [Ln(diphen)1.5(1,10-phen)(H2O)] where Ln = Sm (1), Gd (3), Dy (5), {[Ln(diphen)1.5(1,10-phen)(H2O)]·OH} Ln = Eu (2), Er (7) and {[Ln(diphen)1.5(1,10-phen)(H2O)]·CH3CN·H2O} Ln = Gd (4), Ho (6) (diphen = diphenic acid, 1,10-phen = 1,10 Phenanthroline), were assembled solvothermally by using diphenic acid and 1,10-Phenanthroline as ligands. These lanthanide coordination polymers were characterized by Single-crystal X-ray diffraction, FTIR, Powder X-ray diffraction, Thermogravimetric analysis, UV–visible spectroscopy and Photoluminescence. The CPs 1–7 possess one-dimensional (1D) infinite chain-like structures which crystallize in the monoclinic C2/c space group. The photoluminescence properties of CP 2 exhibit its sensing ability to detect some toxic nitroaromatic compounds and d-block metal ions. However, CP 2 shows highly sensitive behavior for the recognition of Cu2+ and picric acid as indicated by efficient luminescence quenching with the low limit of detection. Other metal ions (viz., Cr3+, Cu2+, Co2+, Zn2+, Mn2+, Ni2+, Cd2+, and Hg2+), and nitro compounds (viz., PA, m-DNB, p-NP, p-NA and NB) were also screened for sensing potential of CP 2.

Tunable valence tautomerism in lanthanide-organic alloys.

The inimitable electronic structures of the lanthanide (Ln) ions are key to advanced materials and technologies involving these elements. The trivalent ions are ubiquitous and are used much more widely than the divalent and tetravalent analogues, which possess vastly different optical and magnetic properties. Hence, alteration of the valence electron count by external stimuli can lead to dramatic changes in materials properties. Compounds exhibiting a temperature-induced complete Ln(III) ⇄ Ln(II) switch, referred to as a valence tautomeric (VT) transition, are rare. Here we present an abrupt and hysteretic VT transition in a lanthanide-based coordination polymer, SmI2(pyrazine)3, driven by the interconversion of Sm(II)-pyrazine(0) and Sm(III)-pyrazine(·-) redox pairs. Alloying SmI2(pyrazine)3 with Yb(II) yields isomorphous Sm1-xYbxI2(pyrazine)3 solid solutions with VT transition critical temperatures ranging widely from 200 K to ∼50 K at ambient pressure. These findings demonstrate a simple strategy to realize thermally switchable magnetic materials with chemically tunable transition temperatures.

Multifunctional 1D lanthanide-based coordination polymers exhibiting single-chain magnets and fluorescence detection

Given the extensive applications of lanthanide-based materials in optics, electricity, magnetism, biomedicine, and other fields, the strategic development of multifunctional lanthanide-based molecular materials through meticulous design of organic ligands and rational selection of Ln3+ ions with distinct characteristics holds significant importance. In this work, a series of 1D chain lanthanide-based polymers {Ln(L)3(H2O)2}n (Ln = Eu for 1, Gd for 2, Tb for 3, Dy for 4) were successfully synthesized by using monomethyl isophthalate (HL) to control the hydrolysis of Ln3+ ions. Magnetic results revealed a weak paramagnetic interaction in 2, an antiferromagnetic coupling in 3, and an intriguing single-chain magnets behavior in 4. Compound 4 characterized an effective energy barrier of 38.08 K without a direct current field. Additionally, compounds 1, 3 and 4 exhibited photoluminescence behaviors, and the photoluminescence quantum yield (PLQY) of 1 was as high as 56 %. Compound 3 exhibited efficient detection of acetylacetone (acac) and nitroarenes through luminescence quenching, achieving the low limits of detection (LOD) of 0.068 μM for acac, 0.142 μM for Nitrobenzene, 0.260 μM for 4-Chloronitrobenzene and 0.276 μM for p-Nitrobenzoic acid. This study successfully prepared multifunctional lanthanide polymers, incorporating magnetic, optical, and sensing properties, by precisely controlling the hydrolysis of Ln3+ ions using organic ligands. These findings not only enrich the repertoire of multifunctional lanthanide-based materials but also broaden their applications in diverse domains.

It's not just the size that matters: crystal engineering of lanthanide-based coordination polymers.

Synthesis and characterization of Lewis base free coordination polymers of selected lanthanides are presented. For this purpose, the substituted CotTIPS ligand (CotTIPS = 1,4-bis-triisopropylsilyl-cyclo-octatetraendiide) was used to synthesize homoleptic, anionic multidecker compounds of the type [K{LnIII(ɳ8-CotTIPS)2}]n. Depending on the solvent used for crystallization and the ionic radii of the lanthanide cations, three different categories of one-dimensional heterobimetallic coordination polymers were obtained in the solid state. For the early lanthanides La and Ce a unique helical conformation was obtained by crystallization from toluene, while the ionic radius of Pr seems to be a turning point towards the crystallization of zigzag polymers. For Er a third structural motif, a trapezoidal wave polymer was observed. Additionally, the zigzag polymer for all compounds could be obtained by changing the solvent from toluene to Et2O, reavealing a correlation between solid-state structure and ionic radii as well as solvent. While photoluminescence (PL) properties of Cot-lanthanide compounds are scarce, the La complexes show ligand centered green luminescence, whereas the Ce complexes reveal deep red emission origin from d-f transitions. The Er-compounds are single-molecule magnets, in which the magnetic relaxation of each Er ion occurs isolated from its neighbors at temperatures above 10 K, while below 9 K a strong antiferromagnetic coupling between the Er ions was seen.

Gd(III)/Dy(III)-based coordination polymers for luminescent and magnetic properties

Two isostructural lanthanide-based coordination polymers, namely, {[Gd2(H2dhtp)3(DMF)2(H2O)4]·2DMF·H2On (1) and {[Dy2(H2dhtp)3(DMF)2(H2O)4]·2DMF·H2O}n (2) (H4dhtp = 2,5-dihydroxyterephthalic acid, DMF = N, N-dimethylformamide) were synthesized and structurally characterized by single-crystal X-ray diffraction, IR, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), and elemental analysis. Compounds 1 and 2 exhibited 3D networks and isostructures, except for the distinction of the metal ion. Magnetic measurements indicated that complex 1 exhibited the dominating contribution at low temperature of zero-field splitting for Gd(III) materials, and the complex 2 shown the depopulation of the excited excited state for Dy(III) material. The solid luminescent properties of H4dhtp, 1, and 2 displayed a blue emission band, while the solution state luminescent properties all demonstrated a green emission band. The combination of luminescence sensing and magnetism in single-phase coordination polymers may offer great potential applications in smart multitasking devices.

Enhancing the Circularly Polarized Luminescence of Europium Coordination Polymers by Doping a Chromophore Ligand into Superhelices.

Lanthanide-based molecular materials showing efficient circularly polarized luminescence (CPL) activity with a high quantum yield are attractive due to their potential applications in data storage, optical sensors, and 3D displays. Herein we present an innovative method to achieve enhanced CPL activity and a high quantum yield by doping a chromophore ligand into a coordination polymer superhelix. A series of homochiral europium(III) phosphonates with a helical morphology were prepared with the molecular formula S-, R-[Eu(cyampH)3-3n(nempH)3n]·3H2O (S/R-Eu-n, n = 0-5%). The doping of chromophore ligand S- or R-nempH2 into superhelices of S/R-Eu-0% not only turned on the CPL activity with the dissymmetry factor |glum| on the order of 10-3 but also increased the quantum yield by about 14-fold. This work may shed light on the development of efficient CPL-active lanthanide-based coordination polymers for applications.

A Doped Lanthanide-Based Coordination Polymer Exhibiting High Relative Sensitivity to Ratiometric Luminescent Thermometers at 440 K.

Ratiometric luminescent thermometers with excellent performance often require the luminescent materials to possess high thermal stability and relative sensitivity (Sr). However, such luminescent materials are very rare, especially in physiological (298-323 K) and high-temperature (>373 K) regions. Here we report the synthesis and luminescent property of [Tb0.995Eu0.005(pfbz)2(phen)Cl] (3), which not only exhibits high Sr in physiological temperature but also has a Sr up to 7.47% K-1 at 440 K, the largest Sr at 440 K in known lanthanide-based coordination compound luminescent materials.

Bifunctional Lanthanide-Based Coordination Polymers: Conversion of CO2 and Highly Selective Luminescence Sensing for Acetylacetone.

A series of bifunctional Ln(III)-based coordination polymers (CPs) {Ln(L)(DMA)2(NO3)}n [Ln(III) = Eu (1), Gd (2), and Dy (3); organic ligand H2L = 2,2'-(1,3,5,7-tetrahydroxyoctahydro-4,8-ethanopyrrolo[3,4-f]isoindole-2,6(1H,3H)-diyl)diacetic acid)] have been successfully synthesized. CPs 1-3 are isostructural and constructed from the dimeric Ln2 unit in which two adjacent LnIII ions are bridged by two μ3-carboxyl oxygens, and the Ln2 dimeric unit is connected by two NO3- ions, four DMA molecules, and four completely protonated L2- ligands forming a 2D layer structure. The magnetic research reveals that CP 2 shows a significant cryogenic magnetocaloric effect (-ΔSm = 22.9 J kg-1 K-1; T = 2.0 K and ΔH = 7.0 T), whereas CP 3 exhibits slow magnetic relaxation property under Hdc = 0 Oe field. Additionally, the luminescence explorations revealed that CP 1 can act as a recyclable luminescent probe for pollutant acetylacetone among various small organic solvent molecules, and the corresponding detection limit is 10-7 mol/L. More importantly, CP 1 also exhibits good catalytic performance in the cycloaddition reaction of CO2 and epoxides or cyanamides under mild conditions. As far as we know, CP 1 represents the first bifunctional lanthanide homogeneous catalyst that can efficiently catalyze the reaction of cyanamides/epoxides with CO2 simultaneously.

Thioflavin-T-Incorporated Cerium-ATP Coordination Polymer Nanoparticles: A Promising System for Detection of Uranyl Ion (UO22+) in Aqueous Medium.

Lanthanide-based coordination polymer nanoparticles (Ln-CPNs) are studied for analytical and biomedical sensing, mainly utilizing the luminescent properties of lanthanides. However, the inclusion of fluorescent guest molecules within the nanoparticles can lead to a stimuli-responsive system with modulated photo-physical properties that can be useful for detecting analytes. In this work, we have synthesized cerium(III) coordination polymer nanoparticles using adenosine triphosphate (ATP) molecules as the ligands. The porous polymeric structure enables CPNs for reversible inclusion and release of thioflavin-T (ThT), which is a weakly emissive dye in the free state but becomes highly emissive when incorporated into the Ce-ATP CPNs. Modulation of the photo-physical properties of ThT-incorporated CPNs in response to the radiotoxic and environmentally alarming uranyl ion (UO22+) has been used for its detection in aqueous medium in the range of 0-20 μM by fluorimetry with an LOD of 80 ng mL-1 (0.34 μM) in deionized water without interference from the most commonly occurring metal ions. Furthermore, the sensing platform has been successfully utilized for UO22+ determination in seawater sample without any pre-treatment and adjustment of pH.

Lanthanide-Based Coordination Polymers Molecular Alloys Stability: A Thermochemical Approach

In this study, we investigate the thermodynamics of lanthanide-based coordination polymer molecular alloys. We demonstrate that if lanthanide ions have many chemical similarities, the solubility of homo-lanthanide-based coordination polymers can vary significantly from one lanthanide ion to another. Indeed, we experimentally determine the solubility constants of a series of isostructural homo-lanthanide coordination polymers, with general chemical formula [Ln2(bdc)3(H2O)4]∞ with Ln = La-Er plus Y and where bdc2- symbolizes 1,4-benzene-di-carboxylate. Then, we extend the study to two series of isostructural molecular alloys with general chemical formula [Ln2xLn'2-2x(bdc)3(H2O)4]∞ with 0 ≤ x ≤ 1 based either on heavy ([Eu2xTb2-2x(bdc)3(H2O)4]∞) or light ( [Nd2xSm2-2x(bdc)3(H2O)4]∞) lanthanide ions. We found that whatever the solubility difference of the homo-nuclear compounds is, the configurational entropy is the main driving force of the stabilization of molecular alloys.

Luminance and Brightness: Application to Lanthanide-Based Coordination Polymers.

Measuring the luminance of lanthanide-based coordination polymers under UV excitation is of prime importance for many technological applications. This study highlights that the quantum yield gives no information about the luminescence intensity of a solid-state compound. Indeed, compounds with high quantum yield can actually be poorly luminescent. Therefore, a brightness calculation or a luminance measurement are mandatory for a quantitative estimation of the luminescence intensity. The calculated brightness appears to be a convenient quantitative parameter for the estimation of the luminescence intensity in the infrared domain, in which luminance is senseless. It is also a useful parameter in the visible domain, but one must keep in mind that only compounds with similar colorimetric coordinates can be compared. For comparing the luminescence intensities of compounds that exhibit different emission colors, the luminance measurement seems to be the most efficient method. A home-made setup that allows this measurement with high reproducibility is described in detail. The luminance of several lanthanide-based coordination polymers with benzene-poly-carboxylate ligands is measured, and the results are compared with brightness and quantum yield measurements. A standard is suggested for calibration.

Application of three Ln(Ⅲ)-coordination polymers in fields of luminescence, antibacteria and detection of Fe3+ and 4-nitrophenol

Three lanthanide-based coordination polymers (Ln-CPs) with layered structure, {[La2(L)3(DMF) (H2O)3]·H2O}n (1), {[Eu2(L)3(DMF)2(H2O)]·(H2O)}n (2) {[Tb2(L)3(DMF)2(H2O)]·H2O}n (3) were successfully synthesized from H2L(N,N′-bis(4-carbozylbenzyl)aniline). Remarkably, compound 3 has extremely high sensitivity to 4-nitrophenol. When the concentration of 4-nitrophenol reaches 5.98 × 10−3 mmol/L, the fluorescence intensity of compound 3 is quenched by 59%. The calculated KSV is 7.56 × 104 and limit of detection (LOD) is 4.73 μg/L. 3 exhibits a highly sensitive detection towards Fe3+ and compound 2 shows outstanding antibacterial effects on Staphylococcus aureus, respectively. The white light emission was also investigated by changing the mixing ratio of LaNO3, EuNO3 and TbNO3 during the preparation of coordination polymers.

New lanthanide-based coordination polymers with 2,5-dihydroxyterephthalate

Crystal growths in gel medium of lanthanide-based coordination polymers with 2,5-dihydroxyterephthalate (dhbdc2−) as ligand lead to two different crystal structures depending on the lanthanide ion. Lanthanide-based coordination polymers that crystallize in these two structural type have respective chemical formulas [Ln2(dhbdc)3(H2O)12·6H2O]∞ with Ln = La-Nd, and [Ln2(dhbdc)3(H2O)8·6H2O]∞ with Ln = Sm-Yb plus Y. Only the Nd-based and the Yb-based coordination polymers exhibit luminescence properties in the near-infrared region.

Self-Assembly of 1D Double-Chain and 3D Diamondoid Networks of Lanthanide Coordination Polymers through In Situ-Generated Ligands: High-Pressure CO2 Adsorption and Photoluminescence Properties.

Two new lanthanide-based coordination polymers, [Sm2(bzz)(ben)6(H2O)3]·0.5H2O (1) and [Eu(bbz)(ben)3] (2), were synthesized and characterized. The described products were formed from in situ-generated benzoate (ben) and N’-benzoylbenzohydrazide (bbz) ligands, which were the products of transformation of originally added benzhydrazide (bzz) under hydrothermal conditions. Compound 1 exhibits a one-dimensional (1D) double-chain structure built up from the connection of the central Sm3+ ions with a mixture of bzz and ben ligands. On the other hand, 2 features a 3D network with a 4-connected (66) dia topology constructed from dinuclear [Eu2(ben)6] secondary building units and bbz linkers. High-pressure CO2 sorption studies of activated 1 show that maximum uptake increases to exceptionally high values of 376.7 cm3 g−1 (42.5 wt%) under a pressure of 50 bar at 298 K with good recyclability. Meanwhile, 2 shows a typical red emission in the solid state at room temperature with the decay lifetime of 1.2 ms.

Microwave-assisted synthesis of anhydrous lanthanide-based coordination polymers built upon benzene-1,2,4,5-tetracarboxylic acid

A series of trivalent lanthanide and group 3 metal coordination polymers with pyromellitic acid [M(Hbtec)]n (M = Eu, Dy, Sm, Nd, Ce, Er, Y) has been synthesized and structurally characterized. Contrary to most of coordination polymers, the reported compounds do not present any crystallized solvent molecules, and consequently they are thermally stable until 400–500 °C. Moreover, they also exhibit good stability in water on a wide pH range. Compounds were synthesized by hydrothermal route with conventional heating but also with microwave-assisted heating, allowing to noticeably reduce the synthesis time to 1 h max. Efforts have been done to obtain nanoparticles with this strategy. Finally, the luminescence properties of the lanthanide counterparts emitting in the visible range (Dy, Sm, Eu) were thoroughly investigated, and the Eu compound exhibit good quantum yield.

Multidimensional Ln-Aminophthalate Photoluminescent Coordination Polymers.

The development of straightforward reproducible methods for the preparation of new photoluminescent coordination polymers (CPs) is an important goal in luminescence and chemical sensing fields. Isophthalic acid derivatives have been reported for a wide range of applications, and in addition to their relatively low cost, have encouraged its use in the preparation of novel lanthanide-based coordination polymers (LnCPs). Considering that the photoluminescent properties of these CPs are highly dependent on the existence of water molecules in the crystal structure, our research efforts are now focused on the preparation of CP with the lowest water content possible, while considering a green chemistry approach. One- and two-dimensional (1D and 2D) LnCPs were prepared from 5-aminoisophthalic acid and Sm3+/Tb3+ using hydrothermal and/or microwave-assisted synthesis. The unprecedented LnCPs were characterized by single-crystal X-ray diffraction (SCRXD), powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM), and their photoluminescence (PL) properties were studied in the solid state, at room temperature, using the CPs as powders and encapsulated in poly(methyl methacrylate (PMMA) films, envisaging the potential preparation of devices for sensing. The materials revealed interesting PL properties that depend on the dimensionality, metal ion, co-ligand used and water content.

Highly Luminescent Europium-Based Heteroleptic Coordination Polymers with Phenantroline and Glutarate Ligands.

Isostructural lanthanide-based coordination polymers with general chemical formula [Ln(phen)(glu)(NO3)]∞ with Ln = La-Tm (except Ce and Pm) have been synthesized by hydrothermal methods (H2glu stands for glutaric acid and phen stands for 1,10-phenantroline). They crystallize in the monoclinic system with the P21/c (no. 14) space group. The crystal structure has been solved on the basis of the La derivative. It can be described as the superimposition of molecular chains of dimeric La(phen)(NO3)-La(phen)(NO3) units bridged by glutarate ligands. Luminescent properties have been explored and show that the Eu derivative exhibits the highest luminance observed for Eu-based coordination polymers (85 to 105 cd·m-2). Effects of the dilution of the Eu3+ and Tb3+ luminescent ions by Gd3+ optically inactive ions are unexpected and to the best of our knowledge unprecedented. This could be related to the different intermetallic energy-transfer mechanisms in competition and to the nonisotropic distribution of the lanthanide ions in these molecular alloys. The investigation of molecular alloys with general chemical formula [Eu1-xTbx(phen)(glu)(NO3)]∞ with 0 ≤ x ≤ 1 highlights a very sizable and constant Eu3+ luminescence whatever the x value, which further confirms the existence of very strong intermetallic energy transfers in this family of compounds. It is also noticeable that some coordination polymers based on weakly emissive lanthanide ions exhibit very well defined emission spectra.

Highlights of the development and application of luminescent lanthanide based coordination polymers, MOFs and functional nanomaterials.

The development of lanthanide based coordination polymer and metal-organic framework (CPs and MOFs) nanomaterials as novel functional (e.g. luminescent and magnetic) materials has attracted significant attention in recent times. This is in part due to the wide, but yet unique coordination requirements that the f-metal ions possess, as well as their attractive physical properties, which are often transferred to the bulk material. Hence, there is no surprise, that the design, synthesis and characterisation of lanthanide based CP/MOF materials (featuring either 'pure' lanthanides, or a mixture of both f- and d-metal ions) for applications in gas and small molecule absorption, storage, conversion/catalysis, chemical sensing, bio-imaging, drug delivery, etc. has been a prominent feature in the scientific literature. In this review, we give a selected overview of some of the recent developments in the area of Ln CP/MOF based nanomaterials for sensing, optical materials and bio-medicine research, as well as making reference to some more established examples, with the view of introducing, particularly to new researchers to the field, the powerful and attractive features of lanthanide based materials.

Lanthanide-based molecular alloys with hydroxyterephthalate: a versatile system

Reactions in water between lanthanide chlorides and the di-sodium salt of 2-hydroxyterephthalic acid (H2hbdc) lead to six families of lanthanide-based coordination polymers depending on the lanthanide ion and the crystal growth method.

Colloidal suspensions of highly luminescent lanthanide-based coordination polymer molecular alloys for ink-jet printing and tagging of technical liquids

A series of lanthanide-based coordination polymer molecular alloy colloidal dispersions usable for ink-jet printing and tagging of technical liquids.