Pillaring of CdCl2‐Like Layers in Lanthanide Metal–Organic Frameworks: Synthesis, Structure, and Photophysical Properties

Mixed-Ligand-Regulated Self-Enhanced Luminous Eu-MOF as an ECL Signal Probe for an Oriented Antibody-Decorated Biosensing Platform

The self-luminescence behavior of lanthanide MOFs (Ln-MOFs) due to the unique antenna effect is considered to be a promising electrochemiluminescence (ECL) emission for biosensors. It is more challenging for Ln-MOFs on account of the difficulty to stimulate Ln ions with the desired energy-transfer efficiency to produce stronger ECL emissions at a low potential. Here, guided by a second ligand-assisted energy-transfer strategy, we present an efficient self-enhanced luminescence mixed-ligand Eu-MOF as an ECL signal probe for an oriented antibody-decorated biosensing platform with a low detection limit and a broad detection range. Diamino terephthalic acid (NH₂-H₂BDC) and 1,10-phenanthroline (Phen) were selected as the first and second ligands, respectively, to form highly conjugated structures, as well as suppress the nonradiative energy transfer. Impressively, Phen precisely adjusts the energy gap between the triplet ligand and the excited state of Eu³⁺, realizing the self-enhancement of ECL efficiency of the Eu-MOF. The mixed ligand adjusted the molar ratio to obtain the stable and strong ECL signal at a lowered triggering potential (0.83 V). In addition, FeCo@CNT features densely active FeCo sites along with a rich hierarchy conductive carbon nanotube (CNT) network, which is efficiently a co-reaction accelerator to produce more TPA^•+ radicals to accelerate the reduction process of the Eu-MOF for achieving the ECL emission amplification. FeCo@CNT with heptapeptide HWRGWVC (HWR) constructed a matrix biosensing interface that allowed the fragment antigen-binding (Fab) regions to target specific antigens and enhance the incubation efficiency. The present study has gone some way toward designing a self-enhanced luminous Eu-MOF, thus giving new fresh impetus to develop high-performance ECL emitters for biological analysis.

Organic-inorganic one-dimensional hybrid aggregates constructed from aromatic-bisphosphonate-functionalized polyoxomolybdates

Five novel lanthanide-substituted polyoxomolybdates (NH₄)₅Na₃H₂[{Ln(H₂O)₇}₂{Mo₅O₁₅(1,4-O₃PCH₂C₆H₄CH₂PO₃)}₄]·nH₂O [Ln = Tb³⁺ (1), Ho³⁺ (2), Er³⁺ (3), Tm³⁺ (4), Yb³⁺ (5); n = 33, 32, 41, 30, 47] have been prepared in a conventional aqueous solution reaction of ammonium molybdate with Ln³⁺ ions and p-xylyenediphosphonic acid. Crystal structure analyses reveal that 1-5 are isomorphic. The prominent architecture characteristic is that their structural units consist of a tetrameric cyclic-shaped [{Mo₅O₁₅(1,4-O₃PCH₂C₆H₄CH₂PO₃)}₄]^16- segment stabilized by two [Ln(H₂O)₇]³⁺ cations, which are connected to propagate one-dimensional chain by Ln³⁺ ions. As is known, compounds 1-5 stand for the first Ln-substituted aromatic-bisphosphonate-functionalized polyoxomolybdates. The solid-state photoluminescence measurement of 1 has been performed at ambient temperature, and it displayed the characteristic emissions of Tb ions based on its 4f-4f transitions. In addition, the magnetic properties of 1-5 compounds show that they all exhibit anti-ferromagnetic interactions.

Luminescent lanthanide metal-organic framework nanoprobes: from fundamentals to bioapplications

Metal-organic frameworks (MOFs), a unique type of porous material characterized by high porosity, large internal surface area and remarkable structural tunability, have emerged as very attractive functional materials for a variety of applications. As a promising subclass of MOFs, lanthanide metal-organic frameworks (Ln-MOFs) integrate the unique advantages of MOFs and the intrinsic features of lanthanide ions, such as sharp emission bands, long luminescent lifetimes, large Stokes shifts, high color purity and high resistance to photobleaching. In this minireview, we provide a brief overview of the most recent advances in luminescent Ln-MOF nanoprobes, which covers from their chemical and physical fundamentals to bioapplications, including their synthetic strategies, optical properties and promising bioapplications in biodetection, bioimaging and therapy. Finally, some of the most important emerging trends and future efforts toward this rapidly evolving field are also envisioned.

Rare-earth metal–organic frameworks: from structure to applications

In the past 30 years, rare-earth metal–organic frameworks (MOFs) have been gaining attention owing to their diverse chemical structures, and tunable properties.

H-shaped oxalate-bridging lanthanoid-incorporated arsenotungstates

A series of oxalate-bridging di-Ln³⁺-incorporated H-shaped polyoxometalates were synthesized and their stability in solution was evidenced by Raman spectroscopy.

Europium-Based Metal-Organic Framework as a Dual Luminescence Sensor for the Selective Detection of the Phosphate Anion and Fe3+ Ion in Aqueous Media

A new three-dimensional europium-based metal-organic framework has been synthesized with the newly designed ligand L (6-[1-(4-carboxyphenyl)-1 H-1,2,3-triazol-4-yl]nicotinic acid). This compound acts as a dual sensor for the phosphate anion and Fe³⁺ ion in aqueous media. The mechanistic aspect of this selectivity and sensitivity was explored through several spectroscopic methods and then correlated with the corresponding structure.

Synthesis and crystal structure of a new polymorph of potassium europium(III) bis(sulfate) mono-hydrate, KEu(SO4)2·H2O

In comparison with the known polymorph of KEu(SO₄)₂·H₂O (monoclinic, P2₁/c), the new polymorph crystallizes in the trigonal crystal system (space group P3₁21).

The mixed-metal sulfate, KEu(SO₄)₂·H₂O, has been obtained as a new polymorph using hydro­thermal conditions. The crystal structure is isotypic with NaCe(SO₄)₂·H₂O and shows a three-dimensional connectivity of the tetra­hedral sulfate units with Eu^III and K^I ions. Tricapped trigonal–prismatic EuO₉ units and square-anti­prismatic KO₈ units link the SO₄ tetra­hedra, building the three-dimensional structure. Topological analysis reveals the existence of two nodes with 6- and 10-connected nets. The compound was previously reported [Kazmierczak & Höppe (2010 ▸). J. Solid State Chem.183, 2087–2094] in the monoclinic space group P2₁/c with a similar structural connectivity and coordination environments to the present compound.

Preparation, characterization, and catalytic performances of a pyrazine dicarboxylate-bridging rare-earth-containing polytungstoarsenate aggregate for selective oxidation of thiophenes and deep desulfurization of model fuels

A new polytungstoarsenate, K₆LiH₆[Ce₄(H₂O)₁₄(pzdc)(H₂pzdc)As₃W₂₉O₁₀₃]·22H₂O (1), was synthesized via a conventional aqueous solution method.

Structure and efficient luminescence upconversion of Ln(iii) aromatic N-oxide coordination polymers

A series of lanthanide-based coordination polymers {[Yb1-xErx(4,4'-bpdo)3(H2O)2](CF3SO3)3}∞ were synthesised by solvent diffusion techniques, where 4,4'-bpdo = 4,4'-bipyridine-N,N'-dioxide, and using differing mole fractions of Yb(iii) and Er(iii) which were systematically varied (x = 0, 0.05, 0.20, 0.50 and 1). All of the materials obtained were characterised using elemental analyses, single-crystal X-ray diffraction (SXRD) and solid-state photoluminescence studies. Structurally, the coordination polymers crystallise as an isomorphous series of infinite 2D sheets, which contain two inner sphere water molecules, and are isostructural with a previously characterised homometallic Yb(iii) compound. In addition to the normal Near Infra-Red (NIR) luminescence, these compounds also demonstrate upconversion emission upon 980 nm excitation. Upconversion luminescence measurements reveal visible emission in the red, green, and blue regions corresponding to the (2)H11/2→(4)I15/2, (4)F9/2→(4)I15/2 and (2)H9/2→(4)I15/2 transitions of the Er(iii) cation upon two and three-photon excitation. We also observed weak emission from the Er(iii) cation in the UV region for the first time in a Ln-MOF based material.

A nonanuclear triangular macrocycle and a linear heptanuclear heterometallic complex based on a 2-substituted imidazole-4,5-dicarboxylate ligand

A Cp*Rh-based nonanuclear triangular macrocycle complex [(Cp*Rh)9L3(NO3)4.5(MeOH)](OTf)4.5 (1), a Cp*Ir-based trinuclear complex [(Cp*Ir)3L(MeCN)4](OTf)3 (2) and a linear heptanuclear heterometallic complex [(Cp*Ir)6ZnL2(MeCN)8(MeOH)2](OTf)8 (3) (Cp* = η(5)-pentamethylcyclopentadienyl) have been synthesized from a 2-(4-(pyridin-4-yl)phenyl)-1H-imidazole-4,5-dicarboxylic acid proligand. These complexes were further characterized by X-ray crystallography, (1)H NMR, DOSY NMR, IR spectroscopy, and elemental analyses.

Metal-Organic Frameworks Modulated by Doping Er(3+) for Up-Conversion Luminescence

Here we present metal-organic frameworks prepared by a one-step synthesis method, possessing both architectural properties of MOF building and up-conversion luminescence of rare earth Er(3+) (hereafter denoted as Up-MOFs). Up-MOFs have characteristic up-conversion emissions at 520, 540, and 651 nm under the excitation of 980 nm owing to the multiple photon absorption. The up-conversion mechanism of these Up-MOFs has been discussed, and it can be attributed to the excited state absorption process. The design and synthesis of Up-MOF materials possessing near-infrared region excitation and up-conversion luminescence are fully expected to be candidates for the advancement of applications in bioimaging, sensors, optoelectronics, and energy conversion/storage devices.

Towards multifunctional lanthanide-based metal-organic frameworks

We report the synthesis, structure and physicochemical attributes of a new holmium(III)-based metal-organic framework whose 3D network structure gives rise to porosity; the reported structure-type can be varied using a range of different lanthanide ions to tune the photophysical properties and produce ligand-sensitised near-infrared (NIR) and visible light emitters.

First quadruple-glycine bridging mono-lanthanide-substituted borotungstate hybrids

A class of novel organic–inorganic hybrid quadruple-glycine lanthanide-substituted Keggin-type borotungstates have been synthesized and characterized.

Preparation, characterization, and properties of PMMA-doped polymer film materials: a study on the effect of terbium ions on luminescence and lifetime enhancement

Poly(methylmethacrylate) (PMMA) doped with Tb-based imidazole derivative coordination polymer {[Tb(3)(L)(μ(3)-OH)(7)]·H(2)O}(n) (1) (L = N,N'-bis(acetoxy)biimidazole) was synthesized and its photophysical properties were studied. The L'(L' = N,N'-bis(ethylacetate)biimidazole) ligand was synthesized by an N-alkylation reaction process followed by ester hydrolysis to produce ligand L. Polymer 1 and ligand L' have been characterized by (1)H NMR and IR spectroscopy, elemental analysis, PXRD and X-ray single-crystal diffraction. Coordination polymer 1 is the first observation of a CdCl(2) structure constructed with hydroxy groups and decorated by ligand L in lanthanide N-heterocyclic coordination polymers. In the 2D layered structure of 1, each Tb3 metal center is connected with three Tb1 and three Tb2 metal centers by seven hydroxyl groups in different directions, resulting in a six-membered ring. After doping, not only the luminescence intensity and lifetime enhanced, but also their thermal stability was increased in comparison with 1. When 1 was doped into poly(methylmethacrylate) (1@PMMA), polymer film materials were formed with the PMMA polymer matrix (w/w = 2.5%-12.5%) acting as a co-sensitizer for Tb(3+) ions. The luminescence intensity of the Tb(3+) emission at 544 nm increases when the content of Tb(3+) was 10%. The lifetime of 1@PMMA (914.88 μs) is more than four times longer than that of 1 (196.24 μs). All τ values for the doped polymer systems are higher than coordination polymer 1, indicating that radiative processes are operative in all the doped polymer films. This is because PMMA coupling with the O-H oscillators from {[Tb(3)(L)(μ(3)-OH)(7)]·H(2)O}(n) can suppress multiphonon relaxation. According to the variable-temperature luminescence (VT-luminescence) investigation, 1@PMMA was confirmed to be a stable green luminescent polymer film material.

Synthesis, crystal structure, and properties of a 1-D terbium-substituted monolacunary Keggin-type polyoxotungstate

A new 1-D linear chainlike terbium-substituted polyoxometalate [Tb(H2O)2(α-PW11O39)](4-) (1) has been synthesized in aqueous solution and characterized by elemental analysis, inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray powder diffraction (XRPD), IR spectrum, thermal analysis, electrospray ionization mass spectrometry (ESI-MS), and X-ray single-crystal diffraction. X-ray structural analysis reveals that 1 displays a 1-D linear chain containing [Tb(H2O)2(α-PW11O39)](4-) moieties. The Tb(III) cation incorporated into the monolacunary Keggin-type [α-PW11O39](7-) unit resides in a distorted monocapped triangular prismatic geometry and acts as a linker to join two adjacent [α-PW11O39](7-) units to form a 1-D chain structure. Solid-state photoluminescent property of 1 has been investigated at room temperature and the photoluminescent emission mainly results from the synergistic effect of the Tb(III) cation and the Na7[α-PW11O39] precursor. The ESI-MS spectrum of 1 confirms that the polyanion [Tb(H2O)(HPW11O39)](3-) is stable in aqueous solution.

Hydrothermal synthesis, X-ray structure and DFT and magnetic studies of a (H2SiW12O40)2− based one-dimensional linear coordination polymer

In this paper, we report the synthesis and characterization of a novel POM-based inorganic–organic hybrid with an in situ transformation of pyridine-2,3-dicarboxylic acid into nicotinic acid and 2-hydroxynicotinic acid under hydrothermal conditions.

Magnetic and luminescent properties of lanthanide coordination polymers with asymmetric biphenyl-3,2′,5′-tricarboxylate

An asymmetric ligand was employed to construct eight (3,6)-connected lanthanide complexes exhibiting slow magnetization relaxation behaviour and characteristic luminescent properties.

A new two-dimensional manganese(II) coordination polymer based on thiophene-3,4-dicarboxylic acid

A novel manganese coordination polymer, poly[(μ5-thiophene-3,4-dicarboxylato)manganese(II)], [Mn(C6H2O4S)]n, was synthesized hydrothermally using 3,4-thiophenedicarboxylate (3,4-tdc(2-)) as the organic linker. The asymmetric unit of the complex contains an Mn(2+) cation and one half of a deprotonated 3,4-tdc(2-) anion, both residing on a twofold axis. Each Mn(2+) centre is six-coordinated by O atoms of bridging/chelating carboxylate groups from five 3,4-tdc(2-) anions, forming a slightly distorted octahedron. The Mn(2+) centres are bridged by 3,4-tdc(2-) anions to give an infinite two-dimensional layer which incorporates one-dimensional Mn-O gridlike chains, and in which the 3,4-tdc(2-) anion adopts a novel hexadentate chelating and μ5-bridging coordination mode. The fully deprotonated 3,4-tdc(2-) anion exhibits unexpected efficiency as a ligand towards the Mn(2+) centres, which it coordinates through all of its carboxylate O atoms to provide the novel coordination mode. The IR spectrum of the complex is also reported.

Hydrogen bonded-extended lanthanide coordination polymers decorated with 2,3-thiophenedicarboxylate and oxalate: synthesis, structures, and properties

Five new LnCPs decorated with H₂tdc and oxalate mixed ligands exhibit a 2D sql layer structure, then the 2D layers are further linked by intermolecule hydrogen bonds to form a 3D supramolecular network with sxb topology.

Rare-earth carboxylates, [Ln2(iii)(μ3-OH)(C4H4O5)2(C4H2O4)]·2H2O [Ln = Ce, Pr and Nd]: synthesis, structure and properties

Three new three-dimensional hybrid compounds, Ln₂(μ₃-OH)(C₄H₄O₅)₂(C₄H₂O₄)]·2H₂O, (Ln = Ce, Pr and Nd) (I²O¹-type) exhibiting proton conductivity and multi-photon up-conversion behaviour have been described.

A series of lanthanide–organic frameworks possessing arrays of 2D intersecting channels within a 3D pillar-supported packed double-decker network and Co2+-induced luminescence modulation

Intersecting channels are observed in the 3D network ofFJU6.