Multifunctional lanthanide coordination polymers

Anisotropic Thermal Expansion of Structurally Related Lanthanide-Mercury(II) Cyanide Coordination Polymers

Three sets of related lanthanide-mercury(II) cyanide coordination polymers were synthesized by the reaction of LnCl3·xH2O (Ln = Ce, Nd, Eu, Gd, Tb, Dy, Ho, Tm, Yb, and Lu) with Hg(CN)2 and structurally characterized. [Ce(OH2)5][Hg(CN)2Cl]3·2H2O is a 3-D material with sheet-based architecture; its thermal expansion behavior shows uniaxial negative thermal expansion (-18.3(8), 39(2), and 68.3(16) ppm K-1 along the a, b, and c axes, respectively). This anisotropic thermal behavior is postulated to be driven elastically by weak Hg···Cl interactions: large area expansion of the sheets causes negative thermal expansion in the perpendicular direction. Using lanthanides heavier than Ce yielded 2-D sheet-based compounds with the formula [Ln(OH2)x]2[Hg(CN)2]5Cl6·2H2O (Ln = Nd and Eu, x = 7; Ln = Gd, Tb, Dy, Ho, Tm, Yb, and Lu, x = 6). Although there was also evidence for elastic behavior within these materials, both showed uniaxial zero thermal expansion (Ln = Nd: 27.9(17), 22.4(10), and 0.6(12) ppm K-1 along the I, II, and III principal axes, respectively; Ln = Tb: 39.6(12), 1.1(17), and 36.1(7) ppm K-1 along the a, b, and c axes, respectively). Despite their similar structural architecture, this zero thermal expansion was found to occur in different directions─within the plane of the 2-D sheets for [Nd(OH2)7]2[Hg(CN)2]5Cl6·2H2O but in the direction perpendicular to the 2-D sheets for [Tb(OH2)6]2[Hg(CN)2]5Cl6·2H2O. Overall, this system of compounds reveals the delicate relationship between coordination polymer structure and thermal expansion.

A facile fluorescence Eu MOF sensor for ascorbic acid and ascorbate oxidase detection

In this work, a facile fluorescence Eu3+-based metal-organic framework (Eu MOF) sensor for ascorbic acid (AA) and ascorbate oxidase (AAO) detection was developed. The fluorescence of the Eu MOF could be effectively quenched by Ce3+ but not by Ce4+ at an appropriate concentration, and thus, when the reductant AA was added into the solution containing Ce4+, Ce4+ was chemically reduced to Ce3+, which induced the decreased fluorescence signal of the Eu MOF. However, when AAO was introduced, AA was effectively oxidized to dehydroascorbic acid (DHAA) under the catalysis of AAO, and thus, Ce4+ could not be reduced, resulting in the fluorescence restoration of the Eu MOF. Hence, the concentration of AA and AAO could be determined by the fluorescence decrease and restoration of the Eu MOF. The fluorescent platform showed high sensitivity with a limit of detection of 0.32 μM for AA and 1.18 U L-1 for AAO, respectively. Moreover, the proposed method was successfully applied for AA and AAO determination in real samples, indicating great potential for biomedical application in complex matrices.

Portable and Recyclable Luminescent Lanthanide Coordination Polymer Film Sensors for Adenosine Triphosphate in Urine

Adenosine triphosphate (ATP) is a small molecule that is released to the urine from bladder urothelial cells and the bladder mucosal band of the human body. In certain cases, ATP can serve as a biomarker in bladder disease. For the practical applicability of luminescent sensors for ATP in urine, it is significant to find a new strategy for making the detection progress simple and available for in-field urine analysis. Here, a novel luminescent lanthanide coordination polymer (Tb-BPA) was designed and synthesized for quick and sensitive detection of ATP through luminescence quenching with a quenching constant of 4.90 × 103 M-1 and a detection limit of 0.55 × 10-6 M. Besides, Tb-BPA has excellent anti-interference ability and can detect ATP in simulated urine with a small relative standard deviation (<4%). Moreover, the luminescent polyacrylonitrile nanofiber films modified by Tb-BPA were prepared by electrospinning and were used for ATP visual detection. Notably, this film is easy to recover and reuse, and maintains good detection performance after at least 7 cycles.

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.

The Construction of a Microbial Synthesis System for Rare Earth Enrichment and Material Applications

Rare earth materials play an irreplaceable role in biomedical and high technology fields. However, typical mining and extraction approaches to rare earth elements (REEs) often lead to severe environmental problems and resource wastage due to the involvement of hazardous chemicals. Although biomining shows elegant alternatives, there are still grand challenges to sustainably isolate and recover REEs in nature because of insufficient metal-extracting microbes and RE-scavenging macromolecular tools. To obtain high-performance rare earth materials directly from rare earth ore, a new generation of biological synthesis strategies needs to be developed for the efficient preparation of REEs. The microbial synthesis system established here has achieved active biomanufacturing of high-purity rare earth products. Further, through employing robust affinity columns bioconjugated with structurally engineered proteins, outstanding separation of Eu/Lu and Dy/La is acquired with the purity of 99.9% (Eu), 97.1% (La), and 92.7% (Dy). More importantly, in situ one-pot synthesis of lanthanide-dependent methanol dehydrogenase is well harnessed and exclusively adsorbs La, Ce, Pr, and Nd in RE tailing for advanced biocatalysis, indicating high value-added application. Therefore, this novel biosynthetic platform provides an insightful roadmap to expand the scope of chassis engineering in terms of biofoundry and to manufacture valuable bioproducts related to REEs.

Tunable White Light Emission of a Metal-Organic Framework Based on a Bisquinoxaline Derivative by Introducing Red-Green Cationic Dyes

The unique structural advantages give metal-organic frameworks (MOFs) a special use as host substrates to encapsulate organic dyes, which would result in specific host-guest composites for white-light phosphors. In this work, an anionic MOF exhibiting blue emission was constructed using bisquinoxaline derivatives as photoactive centers, which could effectively encapsulate rhodamine B (Rh B) and acriflavine (AF) to form an In-MOF ⊃ Rh B/AF composite. By simply adjusting the amount of Rh B and AF, the emitting color of the resulting composite could be easily adjusted. The formed In-MOF ⊃ Rh B/AF composite exhibits broadband white light emission with ideal Commission International ed'Eclairage (CIE) coordinates of (0.34, 0.35), a color rendering index of 80.8, and a moderately correlated color temperature value of 5193.96 K. This strategy can be easily extended to other blue-emitting MOFs and dyes, thus opening up new prospects for the development of white-light-emitting materials.

Unveiling Structural Diversity of Uranyl Compounds of Aprotic 4,4'-Bipyridine N,N'-Dioxide Bearing O-Donors

As an aprotic O-donor ligand, 4,4'-bipyridine N,N'-dioxide (DPO) shows good potential for the preparation of uranyl coordination compounds. In this work, by regulating reactant compositions and synthesis conditions, diverse coordination assembly between uranyl and DPO under different reaction conditions was achieved in the presence of other coexisting O-donors. A total of ten uranyl-DPO compounds, U-DPO-1 to U-DPO-10, have been synthesized by evaporation or hydro/solvothermal treatment, and the possible competition and cooperation of DPO with other O-donors for the formation of these uranyl-DPO compounds are discussed. Starting with an aqueous solution of uranyl nitrate, it is found that an anionic nitrate or hydroxyl group is involved in the coordination sphere of uranyl in U-DPO-1 ((UO₂)(NO₃)₂(H₂O)₂·(DPO)), U-DPO-2 ((UO₂)(NO₃)₂(DPO)), and U-DPO-3 ((UO₂)(DPO)(μ₂-OH)₂), where DPO takes three different kinds of coordination modes, i.e. uncoordinated, monodentate, and biconnected. The utilization of UO₂(CF₃SO₃)₂ in acetonitrile, instead of an aqueous solution of uranyl nitrate, precludes the participation of nitrate and hydroxyl, and ensures the engagement of DPO ligands (4-5 DPO ligands for each uranyl) in a uranyl coordination sphere of U-DPO-4 ([(UO₂)(CF₃SO₃)(DPO)₂](CF₃SO₃)), U-DPO-5 ([UO₂(H₂O)(DPO)₂](CF₃SO₃)₂) and U-DPO-6 ([(UO₂)(DPO)_2.5](CF₃SO₃)₂). Moreover, when combined with anionic carboxylate ligands, terephthalic acid (H₂TPA), isophthalic acid (H₂IPA), and succinic acid (H₂SA), DPO works well with them to produce four mixed-ligand uranyl compounds with similar structures of two-dimensional (2D) networks or three-dimensional (3D) frameworks, U-DPO-7 ((UO₂)(TPA)(DPO)), U-DPO-8 ((UO₂)₂(DPO)(IPA)₂·0.5H₂O), U-DPO-9 ((UO₂)(SA)(DPO)·H₂O), and U-DPO-10 ((UO₂)₂(μ₂-OH)(SA)_1.5(DPO)). Density functional theory (DFT) calculations conducted to probe the bonding features between uranyl ions and different O-donor ligands show that the bonding ability of DPO is better than that of anionic CF₃SO₃ ^-, nitrate, and a neutral H₂O molecule and comparable to that of an anionic carboxylate group. Characterization of physicochemical properties of U-DPO-7 and U-DPO-10 with high phase purity including infrared (IR) spectroscopy, thermogravimetric analysis (TGA), and luminescence properties is also provided.

Self-Assembly of a Two-Dimensional Coordination Polymer Based on Silver and Lanthanide Tetrakis-Acylpyrazolonates: An Efficient New Strategy for Suppressing Ligand-to-Metal Charge Transfer Quenching of Europium Luminescence

A new strategy for the easy polymerization of anionic [Ln(Q^cy)₄]^- (HQ^cy-4-(cyclohexanecarbonyl)-5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one) into two-dimensional layers of [AgLn(Q^cy)₄]_n (Ln = Sm, Eu, Gd, Tb and Dy) is proposed by binding the single molecular anions [Ln(Q^cy)₄]^- to silver cations through the coordination of the pyridinic nitrogen atoms of the pyrazolonate rings. The luminescent properties of [AgLn(Q^cy)₄]_n have been studied in detail, and it was shown that the previously described low photoluminescence quantum yield (PLQY) of [Eu(Q^cy)₄]^- is due to Ligand-To-Metal Charge Transfer (LMCT) quenching, which is effectively suppressed in the heterometallic [AgEu(Q^cy)₄]_n polymer. Sensibilization coefficients for H₃O[Eu(Q^cy)₄], [AgEu(Q^cy)₄]_n, and H₃O[Sm(Q^cy)₄] complexes (n ≈ 1) were estimated via theoretical analysis (also by using Judd-Ofelt theory for Sm³⁺) and PLQY measurements.

Synthesis, Crystal Structure, and Luminescence Properties of the Iso-Reticular Series of Lanthanide Coordination Polymers Synthesized from Hexa-Lanthanide Molecular Precursors

Microwave-assisted reactions in DMSO, between a hexa-lanthanide octahedral complex ([Ln₆(μ₆-O)(μ₃-OH)₈(NO₃)₆(H₂O)₁₂·2NO₃·2H₂O] with Ln = Nd-Yb plus Y) and either 3-halogenobenzoic acid (hereafter symbolized by 3-xbH with x = f or c for fluoro or chloro, respectively) or 4-halogenobenzoic acid (hereafter symbolized by 4-xbH with x = f, c, or b for fluoro, chloro, or bromo, respectively), lead to 1D lanthanide coordination polymers. These coordination polymers are almost iso-reticular. The crystal structure is described on the basis of the coordination polymer with chemical formula [Tb(4-fb)₃(DMSO)(H₂O)₂·DMSO]_∞ obtained from 4-fluorobenzoic acid (4-fbH) and the Tb³⁺-based octahedral complex: It crystallizes in the triclinic system, space group P1̅ (n°2), with the following cell parameters: a = 9.8561(9) Å, b = 10.5636(9) Å, c = 15.1288(15) Å, α = 100.840(3)°, β = 95.552(3)°, γ = 110.482(3)°, V = 1426.4(3) ų, and Z = 2. It can be described on the basis of 1D molecular chains. Luminescence properties of the Tb and Eu derivatives have been measured and compared vs the halogeno-function and its position (meta or para). Some molecular alloys have also been prepared to estimate the strength of the intermetallic energy transfers. To confirm that the hexa-nuclear complexes (and not the halogenated ligand) have a structuring effect for the formation of the straight chain-like molecular motif, another coordination polymer with chemical formula [Tb(4-npa)₃DMSO·DMSO·H₂O]_∞ where 4-npaH symbolizes 4-nitro-phenyl-acetic acid has been prepared. It crystallizes in the triclinic system, space group P1̅ (n°2) with the following cell parameters: a = 7.8784(8) Å, b = 14.8719(16) Å, c = 15.2753(17) Å, α = 73.612(4)°, β = 86.406(4)°, γ = 83.104(4)°, V = 1703.8(3) ų, and Z = 2. Its crystal structure can be described on the basis of a molecular motif that is similar to the one observed in the five previous crystal structures which confirms the structuring effect of the hexa-nuclear complexes.

Lanthanide europium MOF nanocomposite as the theranostic nanoplatform for microwave thermo-chemotherapy and fluorescence imaging

Backgrounds

Microwave sensitization nanoplatform, integrating multiple functional units for improving tumor selectivity, is of great significance for clinical tumor microwave treatment. Lanthanide europium metal organic framework (EuMOF) is expected to be a theranostic nanoplatform owing to its unique luminescent and microwave sensitization properties. However, it is difficult to be applied to complicated biological systems for EuMOF due to its rapid degradation induced by the solvent molecular and ionic environment. In this work, a luminescent EuMOF nanocomposite (EuMOF@ZIF/AP-PEG, named EZAP) was designed, which brought the multifunctional characteristics of microwave sensitization, fluorescence imaging and drug loading.

Results

Lamellar EuMOF was synthesized by a hydrothermal method. Through the charge adsorption mechanism, the zeolite imidazole framework (ZIF) structure was intensively assembled on the surface of EuMOF to realize the protection. Then, through in-situ Apatinib drug loading and PEG modification, EZAP nanocomposite was finally obtained. Apatinib (AP) was a kind of chemotherapy drug approved by Food and Drug Administration for targeted therapy of tumors. PEG modification increased long-term circulation of EZAP nanocomposite. The physical and chemical structure and properties of EuMOF@ZIF (EZ) were systematically represented, indicating the successful synthesis of the nanocomposite. The toxic and side effects were negligible at a safe dose. The growth of human liver cancer cells and murine liver cancer cells in vitro was significantly inhibited, and the combined microwave-thermal therapy and chemotherapy in vivo achieved high anti-cancer efficacy. Moreover, EZAP nanocomposite possessed bright red fluorescence, which can be applied for tumor imaging in tumor-bearing mice in vivo.

Conclusion

Therefore, EZAP nanocomposite showed high microwave sensitization, excellent fluorescence properties and outstanding drug loading capacity, establishing a promising theranostic nanoplatform for tumor therapy and fluorescence imaging. This work proposes a unique strategy to design for the first time a multifunctional nanoplatform with lanthanide metal organic frameworks for biological applications in tumor therapy and diagnosis.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01335-7.

Hexanuclear Molecular Precursors as Tools to Design Luminescent Coordination Polymers with Lanthanide Segregation

Solvothermal reactions between hexanuclear complexes with the general chemical formula [Ln₆(μ₆-O)(μ₃-OH)₈(NO₃)₆(H₂O)₁₂]·2NO₃·2H₂O and 2-bromobenzoic acid (2-bbH) lead to a series of isostructural one-dimensional coordination polymers with the general chemical formula [Ln₂(2-bb)₆]_∞ with Ln = Sm, Eu, Tb, Dy, and Y. These coordination polymers crystallize in the orthorhombic space group Fdd2 (No. 43) with the following cell parameters: a = 29.810(3) Å, b = 51.185(6) Å, c = 11.7913(14) Å, V = 17992(4) ų, and Z = 16. The europium- and terbium-based derivatives show sizable luminescence intensities under UV excitation. Isostructural heterolanthanide coordination polymers have also been prepared. Their luminescent properties suggest that during the synthetic process the starting hexanuclear complexes are destroyed but strongly influence the distribution of the different lanthanide ions over the metallic sites of the crystal structure. Indeed, it is possible to prepare heterolanthanide coordination polymers in which lanthanide-ion segregation is controlled.

New Coordination Polymers of Selected Lanthanides with 1,2-Phenylenediacetate Linker: Structures, Thermal and Luminescence Properties

Solvothermal reactions of lanthanide (III) salts with 1,2-phenylenediacetic acid in N,N'-dimethylformamide (DMF) solvent lead to the formation of the metal complexes of the general formula Ln₂(1,2-pda)₃(DMF)₂, where Ln(III) = Pr(1), Sm(2), Eu(3), Tb(4), Dy(5), and Er(6), 1,2-pda = [C₆H₄(CH₂COO)₂]^2-. The compounds were characterized by elemental analysis, powder and single-crystal X-ray diffraction methods, thermal analysis methods (TG-DSC and TG-FTIR), infrared and luminescence spectroscopy. They exhibit structural similarity in the two groups (Pr, Sm, and Eu; Tb, Dy, and Er), which was reflected in their thermal behaviours and spectroscopic properties. Single-crystal X-ray diffraction studies reveal that Sm(2) and Eu(3) complexes form 2D coordination polymers with four crystallographically independent metal centers. Every second lanthanide ion is additionally coordinated by two DMF molecules. The 1,2-phenylenediacetate linker shows different denticity being: penta- and hexadentate while carboxylate groups exhibit bidentate-bridging, bidentate-chelating, and three-dentate bridging-chelating modes. The infrared spectra reflect divergence between these two groups of complexes. The complexes of lighter lanthanides contain in the structure coordinated DMF molecules, while in the structures of heavier complexes, DMF molecules appear in the inner and outer coordination sphere. Both carboxylate groups are deprotonated and engaged in the coordination of metal centers but in different ways in such groups of complexes. In the groups, the thermal decomposition of the isostructural complexes occurs similarly. Pyrolysis of complexes takes place with the formation of such gaseous products as DMF, carbon oxides, ortho-xylene, ethers, water, carboxylic acids, and esters. The complexes of Eu and Tb exhibit characteristic luminescence in the VIS region, while the erbium complex emits NIR wavelength.

Effect of Different Synthesis Approaches on Structural and Thermal Properties of Lanthanide(III) Metal–Organic Frameworks Based on the 1H-Pyrazole-3,5-Dicarboxylate Linker

The impact of different synthetic procedures such as: hydrothermal, mechanochemical and precipitation on the structure and thermal properties of coordination polymers of 1H-pyrazole-3,5-dicarboxylic acid (H3pdca) with selected lanthanide ions was determined. The prepared complexes of the general formula: Ln2(Hpdca)3⋅nH2O, where Ln = Eu(III), Nd(III), Tb(III) and Er(III); n = 6 or 7 were fully investigated by: elemental analysis, Energy-Dispersive X-Ray (ED-XRF) and infrared (ATR-FTIR) spectroscopy, powder as well as single-crystal X-ray diffraction methods and thermal analysis (TG-DSC and TG-FTIR) in various atmospheres. It was proved that all used strategies offer high yields of reactions along with crystallinity of the obtained products. The X-ray diffraction methods allowed to conclude that the complexes with the same metal ions exhibit the same crystal structure despite different synthesis routes. On the other hand, the coordination polymers of Eu(III), Tb(III) and Er(III) prepared under different conditions are isomorphous. Only neodymium(III) compounds have a different crystal structure. Thermal stability of the produced complexes was correlated with the synthesis conditions, in particular with the way of energy supply. It was found that the highest thermal stability was exhibited by the complexes prepared under the hydrothermal conditions. Additionally, based on the volatile products of metal complexes decomposition, the mechanism of their pyrolysis was proposed in relation to their structures.

Applications of MOFs as Luminescent Sensors for Environmental Pollutants

The environmental pollution has become a serious issue because the pollutants can cause permanent damage to the DNA, nervous system, and circulating system, resulting in various incurable diseases, such as organ failure, malformation, angiocardiopathy, and cancer. The effective detection of environmental pollutants is urgently needed to keep them far away from daily life. Among the reported pollutant sensors, luminescent metal-organic frameworks (LMOFs) with tunable structures have attracted remarkable attention to detect the pollutants because of their excellent selectivity, sensitivity, and recyclability. Although lots of metal-organic framework (MOF)-based luminescent sensors have been summarized and discussed in previous reviews, the detection of environmental pollutants, especially radioactive ions and heavy metal ions, still have not been systematically presented. Here, the sensing mechanisms and construction principles of luminescent MOFs are discussed, and the state-of-the-art MOF-based luminescent sensors of environmental pollutants, including pesticides, antibiotics, explosives, VOCs, toxic gas, toxic small molecules, radioactive ions, and heavy metal ions are highlighted. This comprehensive review may further guide the development of luminescent MOFs and promote their practical applications for sensing environmental pollutants.

Doped Luminescent Lanthanide Coordination Polymers Exhibiting both White-Light Emission and Thermal Sensitivity

Multifunctional lanthanide coordination polymers (CPs) have the advantages of acting in two or more fields simultaneously. Herein, two single lanthanide CPs, formulated as LnL(D/L-Hlac)(H₂O)₂·0.5H₂O (Ln = Eu (1), Tb (2); H₂L = 4,4'-(pyridine-3,5-diyl)dibenzoic acid) and their doped lanthanide analogue Tb_0.9373Eu_0.0627L(D/L-Hlac)(H₂O)₂·0.5H₂O (3) were prepared through hydrothermal methods. Luminescence measurements reveal that 1 displays red photoluminescence and its Commission International ed'Eclairage (CIE) coordinates are almost invariant in the temperature range from 80 to 300 K, while the emission color of 2 changes from yellow to green and its CIE coordinates change from (0.36132, 0.56365) at 80 K to (0.30448, 0.45566) at 300 K. Significantly, 3 not only displays white-light emission with CIE coordinates of (0.32999, 0.33406) but also exhibits a thermal sensitivity of 2.27% K^-1 at 230-300 K. The obviously larger thermal sensitivity in 3 in comparison to that of 1.07% K^-1 for 2 demonstrates that lanthanide CPs with both a heat-sensitive fluorescent thermometer and high-efficiency white-light emission can be expected by doping Eu(III) ions into Tb(III)-based CPs.

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.

Multifunctional Binuclear Ln(III) Complexes Obtained via In Situ Tandem Reactions: Multiple Photoresponses to Volatile Organic Solvents and Anticounterfeiting and Magnetic Properties

The design and synthesis of simple lanthanide complexes with multiple functions have been widely studied and have faced certain challenges. Herein, we successfully synthesized the series of binuclear lanthanide complexes [Ln₂(L1)₂(NO₃)₄] (HL1 = 2-amino-1,2-bis(pyridin-2-yl)ethanol; Ln = Dy (Dy2), Tb (Tb2), Ho (Ho2) Er (Er2)) via the in situ self-condensation of Ln(NO₃)₃·6H₂O-catalyzed 2-aminomethylpyridine (16 steps) under solvothermal conditions. Dy2 was mixed with different volatile organic solvents, and photoluminescence tests demonstrated that it showed an excellent selective photoresponse to chloroform (CHCl₃). Sensing Tb2 on different organic solvents under the same conditions showed that it exhibited excellent selective photoresponse to methanol (CH₃OH). Even under EtOH conditions, Tb2 could selectively respond to small amounts of CH₃OH. To the best of our knowledge, achieving a selective photoresponse to various volatile organic compounds by changing the metal center of the complex is difficult. Furthermore, we performed anticounterfeiting tests on Tb2, and the results showed significant differences between the anticounterfeiting marks under white light and ultraviolet light conditions. The alternating current susceptibilities of Dy2 suggested that it was a typical single-molecule magnet (SMM) (U_eff = 93.62 K, τ₀ = 1.19 × 10^-5 s) under a 0 Oe dc field. Ab initio calculations on Dy2 indicated that the high degrees of axiality of the constituent mononuclear Dy fragments are the main reasons for the existence of SMM behavior.

High Luminance of Heterolanthanide-Based Molecular Alloys by Phase-Induction Strategy

Reactions in water of lanthanide chlorides with the sodium salt of 4,5-dichlorophthalate (dcpa^2-) lead to two families of isostructural coordination polymers: family F1 that gathers compounds with the general chemical formula [Ln₂(dcpa)₃(H₂O)]_∞ with Ln = La-Gd (except Pm) and family F2 that gathers compounds with general chemical formula [Ln₂(dcpa)₃(H₂O)₅·3H₂O]_∞ with Ln = Tb-Lu plus Y. Heterolanthanide molecular alloys that contain both Eu³⁺ and Tb³⁺ ions have been prepared in both structural families. Their luminescence properties have been studied, especially from the brightness point of view. This study revealed that structural family F1 provides molecular alloys that are much more luminescent than those of structural family F2. Therefore, a phase-induction strategy was followed that allowed the design of some molecular alloys (La/Tb/Eu and La/Dy) that are, to the best of our knowledge, among the most luminescent coordination polymers reported so far. This study opens the way to bright luminescent bar codes as well as to bright white luminescent lanthanide-based coordination polymers.

Rational Design of Dual IR and Visible Highly Luminescent Light-Lanthanides-Based Coordination Polymers

A series of isostructural homo- and heterolanthanide coordination polymers of formula [Ln₂(dcpa)₃(H₂O)]_∞ with Ln = La-Gd have been obtained by reactions in water between the lightest lanthanide chlorides and the disodium salt of 4,5-dichlorophthalic acid (H₂dcpa). They present particularly high thermal stability for coordination compounds (up to 400 °C). Their luminescent properties have been studied in detail. Interestingly an insensitivity to water coordination as well as a very strong effect of optical dilution is observed. Therefore, molecular alloys with very high lanthanum concentration have been prepared. Some of them present highly tunable and very intense luminescence. For example, to the best of our knowledge, [Sm_0.04La_1.96(dcpa)₃(H₂O)]_∞ presents one of the highest overall quantum yields measured so far for a Sm³⁺-based coordination compound (Q_Sm^Ligand = 9.2%), and [Nd_0.03Sm_0.14Eu_0.03La_1.8(dcpa)₃(H₂O)]_∞ is one of the brightest (12 Cd·m^-2 under 0.75 mW·cm^-2 UV flux) multiemissive visible and near-infrared lanthanide-coordination polymers reported to date.

Magnetic and Luminescent Properties of Isostructural 2D Coordination Polymers Based on 2-Pyrimidinecarboxylate and Lanthanide Ions

A couple of isostructural coordination polymers with the general formula [Ln4(pymca)4(AcO)8]n have been obtained from reactions between pyrimidine-2-carboxylate (pymca) ligand and rare-earth ions (Ln = Dy (1), Nd (2)). These two-dimensional compounds have been characterized and the crystal structures have been solved by single-crystal X-ray diffraction technique, resulting in layers along the bc plane based on pymca and acetate anions that act as bridging ligands between metal atoms. Given that pymca and acetate anions possess carboxylate and hetero-nitrogen groups, it is possible to build a coordination polymer whose metal centers have a nine coordination. Furthermore, static and dynamic magnetic measurements of compound 1 reveal the lack of single molecule-magnet (SMM) behavior in this system due to the following two effects: (i) the ligand field does not stabilize magnetic ground states well separated from excited states, and (ii) anisotropy axes are not collinear, according to results with Magellan software. On another level, luminescent properties of compounds 1 and 2 are attributed to singlet π-π* transitions centered on pymca ligand as corroborated by time-dependent density functional theory (TD-DFT) calculations.

Interpenetrated Metal-Organic Frameworks with Topology and Versatile Functions

Through an "isoreticular expansion" strategy, a large number of highly porous zirconium-based metal-organic frameworks (Zr-MOFs) have been achieved using extended organic linkers in the past few years. However, interpenetrated Zr-MOFs with ftw topology have scarcely been reported, mainly owing to the used bulky tetratopic linkers that effectively prevent the network interpenetration. Here, we report a new family of zirconium and lanthanide (Ln) MOFs with ftw topology, constructed by hexanuclear Zr or Ln (Ln = Eu, Tb, Gd, Dy, Tm, Yb, Nd, and Er) clusters and a spirobifluorene-center tetracarboxylate linker. Our studies reveal that the isostructural Zr and Ln MOFs are all doubly interpenetrated with ultrahigh thermal and chemical stability. The observed unusual interpenetration can be attributed to the specific geometry of the spirobifluorene-center tetratopic linker. Gas adsorption studies show that the interpenetrated Zr-MOF is still highly porous and exhibits high performance for CO₂ storage, which can be attributed to the strong CO₂ binding environment contributed by the reduced pore size. In addition, the presented MOFs display strong characteristic luminescence in the UV-vis-NIR region. Moreover, the incorporation of the spiro-center linker into the framework can efficiently produce two-photon-excited photoluminescence with a large action cross-section value, which also benefited from the high packing density of the nonlinear optical chromophore linker in the interpenetrated structure.

Fluorescence Turn-On Detection of Ascorbic Acid Using a Self-Assembled Lanthanide Polymer Nanoparticle

Ascorbic acid (AA), or vitamin C, is an important reactive biological molecule in vivo, and an abnormal level of AA is associated with many diseases. Therefore, the rapid, sensitive, and selective detection of AA levels is of significance in cases of medical assay and diagnosis. Compared with other nanoparticles, lanthanide coordination polymer nanoparticles (Ln-CPs) have been demonstrated as the excellent biomolecule sensing platforms due to their unique optical properties and intrinsic porosities. In this work, the cerium coordination polymer nanoparticles ATP-Ce-Tris were synthesized in a simple and quick way. The synthesized ATP-Ce-Tris nanoparticle shows the characteristic peak of Ce³⁺ located at 365 nm, which is corresponding to the 4f→5d transition of Ce³⁺. In the presence of Fe³⁺, the fluorescence of ATP-Ce-Tris quenched, and the following added ascorbic acid (AA) makes it restoring effectively. Based on this, we constructed a fluorescence probe with excellent sensitivity for AA sensing in a wide linear relationship from 0.05 to 500 μM. The detection limit was as low as 18 nM (signal-to-noise ratio of three), which is one or two orders of magnitude lower than those of reported sensors. The proposed sensing systems also exhibits excellent sensitivity for AA detection in human serum sample, exploiting a valuable platform for AA analysis in clinic diagnostic and drug screening.

The chemistry of Ce-based metal-organic frameworks

Metal-organic frameworks (MOFs) have gained widespread attention due to their modular construction that allows the tuning of their properties. Within this vast class of compounds, metal carboxylates containing tri- and tetravalent metal ions have been in the focus of many studies due to their often high thermal and chemical stabilities. Cerium has a rich chemistry, which depends strongly on its oxidation state. Ce(iii) exhibits properties typically observed for rare earth elements, while Ce(iv) is mostly known for its oxidation behaviour. In MOF chemistry this is reflected in their unique optical and catalytic properties. The synthetic parameters for Ce(iii)- and Ce(iv)-MOFs also differ substantially and conditions must be chosen to prevent reduction of Ce(iv) for the formation of the latter. Ce(iii)-MOFs are usually reported in comprehensive studies together with those constructed with other RE elements and normally they are isostructural. They exhibit a greater structural diversity, which is reflected in the larger variety of inorganic building units. In contrast, the synthesis conditions of Ce(iv)-MOFs were only recently (2015) established. These lead selectively to hexanuclear Ce-O clusters that are well-known for Zr-MOFs and therefore very similar structural and isoreticluar chemistry is found. Hence Ce(iv)-MOFs exhibit often high porosity, while only a few porous Ce(iii)-MOFs have been described. Some of these show structural flexibility which makes them interesting for separation processes. For Ce(iv)-MOFs the redox properties are most relevant. Thus, they are intensively discussed for catalytic, photocatalytic and sensing applications. In this perspective, the synthesis, structural chemistry and properties of Ce-MOFs are summarized.

Water-stable LnIII-based coordination polymers displaying slow magnetic relaxation and luminescence sensing properties

Six Ln-CPs were synthesized: Dy-CP shows slow magnetic relaxation, and Eu-CP and Tb-CP exhibit recyclable and multi-responsive sensing for Fe³⁺, MnO₄⁻, Cr^VI-anions (CrO₄²⁻, Cr₂O₇²⁻) and TNP in an aqueous system.

Self-assembly of a terbium(III) 1D coordination polymer on mica

The terbium(III) ion is a particularly suitable candidate for the creation of surface-based magnetic and luminescent devices. In the present work, we report the epitaxial growth of needle-like objects composed of [Tb(hfac)₃·2H₂O] _n (where hfac = hexafluoroacetylacetonate) polymeric units on muscovite mica, which is observed by atomic force microscopy. The needle-like shape mimics the structure observed in the crystalline bulk material. The growth of this molecular organization is assisted by water adsorption on the freshly air-cleaved muscovite mica. This deposition technique allows for the observation of a significant amount of nanochains grown along three preferential directions 60° apart from another. The magnetic properties and the luminescence of the nanochains can be detected without the need of surface-dedicated instrumentation. The intermediate value of the observed luminescence lifetime of the deposits (132 µs) compared to that of the bulk (375 µs) and the CHCl₃ solution (13 µs) further reinforces the idea of water-induced growth.

Waste PET as a Reactant for Lanthanide MOF Synthesis and Application in Sensing of Picric Acid

In this study, a lanthanide metal organic framework based on the ligand of terephthalic acid derived from waste polyethylene terephthalate (PET) bottles was designed and synthesized. The structure and morphology of the Tb-BDC was investigated by X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The Tb-BDC displays a high selectivity and sensitivity towards picric acid (TNP). The luminescence intensities exhibit a linear relation, with a concentration of TNP over the range of 1 × 10^-5-1 × 10^-4 M, with a limit of detection of 1 × 10^-5 M. The sensing mechanism is also discussed. This is the first time that waste PET materials have been used as the starting precursor of terephthalic acid (BDC) for the fabrication of lanthanide MOF (metal organic framework), which is applied in sensing TNP.

Comprehensively understanding the steric hindrance effect on the coordination sphere of Pb2+ ions and photophysical nature of two luminescent Pb(ii)-coordination polymers

New luminescent Pb(ii)-coordination polymers (Pb(ii)-CPs), [Pb(2-anc)₂]_n (1) and [Pb(3-qlc)₂(H₂O)₂]_n (2) (2-anc = 2-aminonicotinate, 3-qlc = 3-quinolinecarboxylate), were synthesized by a solvothermal reaction and characterized using microanalysis, IR spectrometry and thermogravimetric analysis. Single crystal structure analysis revealed that the Pb²⁺ ion displays a hemi-directed coordination geometry in 1 and a holo-directed coordination geometry in 2. The difference between the coordination spheres of 1 and 2 is related to the steric hindrance effect of the ligands. A two-dimensional (2D) corrugated layer structure is formed in 1, and the neighboring layers are further extended into a three-dimensional (3D) van der Waals crystal by ππ interactions between the pyridyl rings in the neighboring layers. In contrast, a one-dimensional (1D) coordination polymeric chain is formed in 2, and the adjacent chains are connected in a 2D network by hydrogen bonds. The photophysical properties of 1 and 2 were studied at ambient conditions, disclosing that 1 emits phosphorescence at 548 nm with a millisecond-scale emission lifetime and an absolute quantum yield of 2.2%; 2 emits only blue fluorescence with an absolute quantum yield of 3.5% and nanosecond-scale emission lifetime. The reasons for the difference in the photophysical nature of 1 and 2 are discussed in regards to the electron band structure and density of states analysis.

Structural investigation of one- and three-dimensional lanthanide(III) coordination polymers based on functionalized terpyridine carboxylate and aromatic dicarboxylate ligands

Three series of lanthanide coordination polymers, namely catena-poly[[lanthanide(III)-μ2-(benzene-1,2-dicarboxylato)-μ2-[2-(2,2′:6′,2′′-terpyridin-4′-yl)benzoato]] monohydrate], {[Ln(C8H4O4)(C22H14N3O2)]·H2O} n or {[Ln(1,2-bdc)(L)]·H2O} n , with lanthanide (Ln) = dysprosium (Dy, 1), holmium (Ho, 2) and erbium (Er, 3), poly[bis(μ2-benzene-1,3-dicarboxylato)bis[μ2-2-(2,2′:6′,2′′-terpyridin-4′-yl)benzoato]dilanthanide(III)], [Ln2(C8H4O4)2(C22H14N3O2)2] n or [Ln2(1,3-bdc)2(L)2] n , with Ln = gadolinium (Gd, 4), Ho (5) and Er (6), and poly[(μ2-benzene-1,4-dicarboxylato)[μ2-2-(2,2′:6′,2′′-terpyridin-4′-yl)benzoato]lanthanide(III)], [Ln(C8H4O4)(C22H14N3O2)] n or [Ln(1,4-bdc)(L)] n , with Ln = Dy (7), Ho (8), Er (9) and ytterbium (Yb, 10), were synthesized under hydrothermal conditions and characterized by elemental analysis, IR and single-crystal X-ray diffraction. Compounds 1–3 possess one-dimensional loop chains with Ln2(COO)2 units, which are extended into three-dimensional (3D) supramolecular structures by π–π interactions. Isostructural compounds 5 and 6 show 6-connected 3D networks, with pcu topology consisting of Ln2(COO)2 units. Compounds 7–10 display 8-connected 3D frameworks with the topological type rob, consisting of Ln2(COO)2 units. The influence of the coordination orientations of the aromatic dicarboxylate groups on the crystal structures is discussed.