Hydrothermal Synthesis, Structure, and Optical Properties of Two Nanosized Ln 26 @CO 3 (Ln=Dy and Tb) Cluster‐Based Lanthanide–Transition‐Metal–Organic Frameworks (Ln MOFs)

Self-Assembly of Lanthanide-Aluminum Cluster-Organic Frameworks with Magnetocaloric Effect and Luminescence

The self-assembly of the lanthanide metal-organic frameworks presents a formidable challenge but profound significance. Compared with the metal-organic frameworks based on 4f-3d ions, the chemistry of 4f-3p metal-organic frameworks has not been fully explored so far. In this study, two lanthanide-aluminum-based clusters [Ln6Al(IN)10(μ3-OH)5(μ3-O)3(H2O)8]·xH2O (x = 2, Ln = Gd, abbreviated as Gd6Al; x = 2.5, Ln = Eu, abbreviated as Eu6Al; HIN = isonicotinic acid) have been meticulously designed and obtained by hydrothermal reaction at low pH. The crystallographic study revealed that both Gd6Al and Eu6Al clusters exhibit an unprecedented sandwiched metal-organic framework holding a highly ordered honeycomb network. To our knowledge, it is the first case of Ln-Al-based cluster-organic frameworks. Furthermore, magnetic investigation of Gd6Al manifests a decent magnetic entropy change of -ΔSmmax = 28.8 J kg-1 K-1 at 2 K for ΔH = 7.0 T. Significantly, the introduction of AlIII ions into the lanthanide metal-organic frameworks displays excellent solid-state luminescent capability with a lifetime of 371.6 μs and quantum yield of 6.64%. The construction and investigation of these two Ln-Al clusters represent great progress in the 4f-3p metal-organic framework.

Gradual Size Enlargement of Aluminum-Oxo Clusters and the Photochromic Properties

Metallic clusters, assembled by functional motifs, possess the attribute of regulating the properties by changing inorganic and organic components. In this work, a series of aluminum-oxo clusters, [Al₆O(dmp)₄(Hdmp)₂]·2ⁱPrOH [Al₆-1, H₃dmp = 2,2-bis(hydroxymethyl)propionic acid], [Al₆(H₂thmmg)₆]·2DMF·2H₂O [Al₆-2, H₅thmmg = N-tris(hydroxymethyl)methylglycine], [Al₈(OH)₄(NAP-OH)₁₂(MeO)₇(MeOH)]Cl·7MeCN·3MeOH (Al₈, HNAP-OH = 3-hydroxy-2-naphthoic acid), and [Al₁₀(NA)₁₀(MeO)₂₀] (Al₁₀, HNA = nicotinic acid), were obtained based on different carboxylic acids, realizing metallic ring size enlargement from 5.91 to 9.32 Å. They all exhibit good chemical stability. Importantly, the Al₈ cluster displays obvious photochromic behavior from pale yellow to orange yellow, originating from the generation of photoinduced radicals in the metal-assisted ligand-ligand electron transfer process of 3-hydroxy-2-naphthoic acid (HNAP-OH). This work enriches the metal ring cluster chemistry and reports the example of the aluminum-oxo cluster-based photochromic material, developing a novel system of photochromic materials.

Discrete Arsonate-Grafted Inverted-Keggin 12-Molybdate Ion [Mo12O32(OH)2(4-N3C2H2-C6H4AsO3)4]2- and Formation of a Copper(II)-Mediated Metal-Organic Framework

The discrete inverted-Keggin ion [Mo₁₂O₃₂(OH)₂(4-N₃C₂H₂-C₆H₄AsO₃)₄]^2- (1) has been prepared in an aqueous acidic (pH 0.8) medium by the reaction of MoO₃ with the (4-triazolylphenyl)arsonic acid 4-N₃C₂H₂-C₆H₄AsO₃H₂ under hydrothermal conditions and was isolated as a sodium salt in 21% yield. The exact same reaction in the presence of Cu²⁺ ions resulted in the neutral metal-organic framework (MOF) Cu₂[Mo₁₂O₃₄(4-N₃C₂H₂-C₆H₄AsO₃)₄] (Cu-1) in 68% yield. The inverted-Keggin ion 1 comprises a metal-oxo core, which is capped by four organoarsonate groups, and in Cu-1, individual polyanions are linked in the solid state by coordination of the Cu²⁺ ions with the triazolyl groups. The discrete ion 1 was characterized by single-crystal X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and atomic absorption (AA) spectroscopy, as well as thermogravimetric analysis (TGA), and the POM-MOF Cu-1 was characterized by single-crystal and powder XRD, FT-IR, TGA, and gas sorption. Cu-1 has channels with a diameter of around ∼0.9 nm and exhibits a water-vapor adsorption capacity of 89.7 cm³ g^-1 (p/p₀ = 0.95).

Novel lanthanide nanoparticle frameworks for highly efficient photoluminescence and hypersensitive detection

Despite the excellent luminescent properties of lanthanide clusters (LnCs), their suprastructures that inherit their characteristic luminescent properties are scarcely reported. Herein, novel and highly luminescent suprastructures are synthesized via a two-step assembly method to incorporate LnCs in covalent organic frameworks (COFs). COFs are pre-synthesized and decorated with rigid anchoring groups on their nanochannel walls, which provide one-dimensional confined spaces for the subsequent in situ assembly of luminescent LnCs. The confined LnCs are termed nanoparticles (NPs) to distinguish them from the pure LnCs. Secondary micropores with predictable sizes are successfully formed between the walls of the nanochannels and the orderly aligned NPs therein. By using a small organic ligand that can efficiently sensitize Ln(iii) cations in the assembly processes, the obtained composites show high quantum yields above 20%. The fluorescence can even be effectively maintained across nine pH units. The secondary micropores further enable the unambiguous discrimination of six methinehalides and ultrasensitive detection of uranyl ions. This study provides a new type of luminescent material that has potential for sensing and light emitting.

A cyanometallate- and carbonate-bridged dysprosium chain complex with a pentadentate macrocyclic ligand: synthesis, structure, and magnetism

A novel one-dimensional polymeric cyanometallate- and carbonate-bridged dysprosium(iii) chain with a pentadentate macrocyclic ligand exhibits field-induced multiple-relaxation processes.

A robust 3D zinc(II)-organic framework for efficient dual detection of acetylacetone and Tb3+ ions

There has been broad attention to the recognition and detection of ions and organic small molecules due to their essential roles in environmental systems. However, dual-functional probes have seldom been developed for sensing organic constituents and lanthanide ions. A new 3D pillared Zn(ii)-organic framework [Zn3(L)(DCTP)3]n (1) (L = 1,4-di(1H-benzo[d]imidazol-2-yl)butane and H2DCTP = 2,5-dichloroterephthalic acid) was hydrothermally synthesized and structurally characterized, and features a unique 3D 4,4,4,6-connected framework containing approximately 9.99 × 9.78 Å2 cubic channels. 1 displays excellent thermal and pH stability and can act as a novel "turn-on" fluorescent probe for highly selectively sensitizing Tb3+ ions through an "antenna effect". Furthermore, 1 is a dual-response fluorescent sensor for monitoring acetylacetone and Tb3+ ions with rapid response times (within 1 min), low limits of detection (LOD) (5.02 × 10-6/1.15 × 10-8 M, separately) and great anti-interference ability and recyclability towards the analytes. The related sensing mechanisms for detecting analytes are also investigated in detail.

Assembly of Chiral Cluster-Based Metal-Organic Frameworks and the Chirality Memory Effect during their Disassembly

Many metal clusters are intrinsically chiral but are often synthesized as a racemic mixture. By taking chiral Ag₁₄(SPh(CF₃)₂)₁₂(PPh₃)₄(DMF)₄ (Ag₁₄) clusters with bulky thiolate ligands as an example, we demonstrate herein an interesting assembly disassembly (ASDS) strategy to obtain the corresponding, optically pure crystals of both homochiral enantiomers, R-Ag_14m and S-Ag_14m. The ASDS strategy makes use of two bidentate linkers with different chiral configurations, namely, (1R,2R,N¹E,N²E)-N¹,N²-bis(pyridin-3-ylmethylene)cyclohexane-1,2-diamine (LR) and the corresponding chiral analogue LS. For comparison, we also use the racemic mixture of equimolar of LR and LS (LRS). Three three-dimensional (3D) Ag₁₄-based metal-organic frameworks (MOFs) were characterized by X-ray crystallography to be [Ag₁₄(SPh(CF₃)₂)₁₂(PPh₃)₄(LR)₂]_n (Ag₁₄-LR), [Ag₁₄(SPh(CF₃)₂)₁₂(PPh₃)₄(LS)₂]_n (Ag₁₄-LS), and [Ag₁₄(SPh(CF₃)₂)₁₂(PPh₃)₄(LRS)₂]_n (Ag₁₄-LRS), respectively. As expected, the building blocks in Ag₁₄-LR or Ag₁₄-LS are homochiral R-Ag₁₄ or S-Ag₁₄, respectively. In contrast, Ag₁₄-LRS is achiral and crystallizes with a diamond-like structure containing alternate R-Ag₁₄ and S-Ag₁₄ clusters. During the assembly process, the racemic Ag₁₄ clusters were converted to homochiral building blocks, namely, R-Ag₁₄ for Ag₁₄-LR and S-Ag₁₄ for Ag₁₄-LS. Subsequently, the chiral linkers were removed from the crystals of Ag₁₄-LR and Ag₁₄-LS via hydrolysis with water, and from the disassembled solid material Ag₁₄-DR and Ag₁₄-DS, optically pure enantiomers R-Ag_14m and S-Ag_14m were obtained. It is hoped that this simple assembly strategy can be used to construct cluster-based chiral assemblage materials and that the subsequent disassembly protocol can be used to obtain optically pure chiral cluster molecules from as-prepared racemic mixtures.

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.

A highly selective and sensitive fluorescent sensor based on Tb3+-functionalized MOFs to determine arginine in urine: a potential application for the diagnosis of cystinuria

A unique metal-organic framework with the formula [Cd₄(H₂L)₂(L)·H₂O]·3H₂O (H₄L = 5,5'-(1H-1,2,4-triazole-3,5-diyl)diisophthalic acid) was successfully constructed under solvothermal conditions. The frameworks with multiple free Lewis base sites and Lewis acid sites exhibited easily sensitized properties. After the encapsulation of Tb³⁺ cations, the as-synthesized Tb³⁺@Cd-MOF demonstrated strong luminescence induced by the efficient energy transfer from the bridging ligands to the Tb³⁺ cations, with the potential to serve as a chemical sensor. Interestingly, Tb³⁺@Cd-MOF was proven to be a very promising and highly selective and sensitive luminescent platform for the quantitative detection of arginine, which is the biomarker of cystinuria. The fluorescent probe presented high selectivity to arginine in urine with strong luminescence quenching. Furthermore, a convenient fluorescence-based test paper for the visual detection of arginine in applications was prepared. For the first time, arginine was quantified and monitored in urine by a highly efficient recyclable fluorescent sensor based on Tb³⁺-functionalized MOF hybrids, which may be a potential candidate for the further development of clinical diagnostic tools.

Induced Aggregation and Synergistic Coordination Strategy in Cluster Organic Architectures

Developments in strategies for the synthesis of oxo-hydroxo lanthanide (Ln) clusters during the past few decades have resulted in abundant relevant crystalline materials that exhibit attractive structures and interesting properties. The combination of these oxo-hydroxo Ln clusters and organic ligands has led to the formation of new extended arrays of Ln cluster organic frameworks (LnCOFs). In contrast to metal-organic frameworks, the incorporation of particular characteristics of clusters provides the opportunity to develop performances not available in single-metal compounds. Even with steady advances in oxo-hydroxo Ln clusters, progress in LnCOFs is less developed. To obtain LnCOFs, one premise is to induce the oxophilic Ln ions undergoing aggregation. Meanwhile, the organic ligands should have extra coordination sites for further expansion. Multidentate organic ligands like pyrazinecarboxylic acid and pyridinecarboxylic acid containing O and N donors will meet these two requirements. Their carboxyl groups will induce the aggregation of Ln ions, while the N donors can serve as potential extension sites. To make more open frameworks or if the oxo-hydroxo Ln clusters fail to be congregated or connected, then a second ligand is necessary. The introduction of the suitable second ligand may occupy a partial coordination sphere of Ln ions and ultimately benefit the connection process. In this Account, we introduce the origin and evolution of the induced aggregation and synergistic coordination strategy. According to the attributes of the organic ligands in the documented LnCOFs, we classify them into linear and nonlinear groups in the second and third parts. From the aspect of ligand-induced aggregation, isonicotinic acid (HIN) and lengthened 4-(4-pyridyl)benzoic acid (HPBA) ligands as well as their nonlinear analogues are settled as typical models. From the aspect of synergistic coordination, chelating ligands like 1,2-benzenedicarboxylic acid (1,2-H₂BDC) and acetic acid (HOAc) play significant roles. Moreover, three types of synergistic coordination are discussed in detail: synergistic coordination between two types of organic ligands, synergistic coordination between organic and inorganic ligands, and simultaneous synergistic coordination of aforementioned two types. From the aspect of LnCOF products, in addition to traditional pure LnCOFs, new types of heterometallic frameworks containing two types of cluster building units have been developed. Although this Account focuses on the nuclearity and coordination aspects of LnCOFs, we anticipate that it will stimulate more efforts in the further study of their properties beyond the exploratory synthesis. More importantly, synergistic coordination may be applied to other systems and inspire crystal design and targeted assembly of new functional materials.

Two novel bi-functional hybrid materials constructed from POMs and a Schiff base with excellent third-order NLO and catalytic properties

The first polyoxometalates modified by a porphyrin-resembling planar Schiff base have been successfully designed and synthesized under hydrothermal conditions. The third-order NLO responses indicated that they are excellent third-order NLO materials. Their catalytic performances are also investigated.

Photochromism, photoluminescence modulation and selective recognition of small molecules of two highly stable dynamic metal–organic frameworks

Two highly stable dynamic Ln-MOFs show photochromism, tunable photoluminescence, and selective recognition of small molecules.

Two hybrid polyoxometalates constructed from Preyssler P5W30 clusters and Schiff base exhibiting interesting third-order NLO properties

Two novel inorganic–organic hybrid NLO materials constructed from Preyssler-type P₅W₃₀ cluster anions and Schiff-base have been isolated under hydrothermal conditions.

Syntheses and crystal structures of two new silver–organic frameworks based on N-pyrazinesulfonyl-glycine: weak Ag···O/N interaction affecting the coordination geometry

Two new metal–organic frameworks, namely, [Ag2(L)] n (1) and {[Ag2.5(L)(bpy)2]·(NO3)0.5·(H2O)4.5} n (2), where H2L=N-pyrazinesulfonyl-glycine and bpy=4,4′-bipyridine, have been synthesized and characterized by single-crystal X-ray diffraction, IR spectroscopy, and elemental analysis. X-ray diffraction crystallographic analyses indicate that 1 displays a silver carboxylate-sulfonamide layer structure containing an uncommon heptanuclear [Ag7] cluster wherein four silver(I) atoms form an Ag4 plane with in a three-connected (6, 3) net. The molecular structure of 2 has three crystallographically independent two-coordinate Ag centers with an intersecting Ag-bpy chain structure in a six-connected (3, 6) or a four-connected (4, 4) topology. The L2− ligand serves as a μ 7-(η 2-O,N), (η 2-O′,N′), O,O″,O″′,N,N″ ligand in 1 and as a μ 3-(η 2-O,N), N,O′ ligand in 2. In the crystal, a 3D supramolecular architecture is formed by coordinative bonding in 1, but through O–H···O bonding as well as π···π stacking in 2. The two compounds show a combination of coordinative bonds, ligand-supported Ag···Ag interactions and weak Ag···O/N coordinative interactions in the solid state.

Design, synthesis and excellent third-order NLO properties of two new polyoxometalates constructed from Keggin polyanions bonded by a solvent molecule

Two new monosubstituted Keggin structural polyoxometalates [H5PMo11O39Zn(C5H5N)]·(C5H5N)5·H2O (1) and [H5PW11O39Co(C5H5N)]·(C5H5N)2·(C6H8N)2·1.5CH3OH (2) have been successfully synthesized under hydrothermal conditions. Structural analysis indicates that the polyoxoanion of compound 1 is a solvent molecule-bonded zinc-monosubstituted Keggin structural cluster, [PMo11O39Zn(C5H5N)](5-), while the polyoxoanion of compound 2 is a cobalt-monosubstituted phosphotungstate polyanion bonded with one pendant pyridine molecule. Both 1 and 2 show 3D supramolecular interpenetrating structures constructed of inorganic polyanion layers and organic layers. Very interestingly, compounds 1 and 2 exhibit excellent third-order NLO properties, and the TPA cross section σ of 1 and 2 is 2571.3 GM and 2876.3 GM, respectively.

pH-Dependent Self-Assembly of Ladder-Like Lanthanide Chains with Copper(I) Halide Clusters

Through adjustment of the pH value of the reaction system, two series of 3 D lanthanide(III)-copper(I) coordination polymers, namely [Ln₂ (na)₇ Cu₆ Br₅ (H₂ O)₂ ] [Ln=La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8)] and [La₂ (na)₇ Cu₃ Br₂ (H₂ O)₂ ]⋅H₂ O (9) (na^- =nicotinate), are synthesized hydrothermally and characterized fully. It is worth nothing that these two series of heterometallic compounds are constructed from similar ladder-like Ln-organic chains, but different copper(I) halide clusters. The luminescence properties of the compounds with Nd (4), Eu (6), and Tb (8) are also investigated.

Sodalite-like rare-earth carbonates: a study of structural transformation and diluted magnetism

A series of novel rare earth carbonates, RE3(OH)6(CO3)Cl (RE = Dy, Er, Y), with sodalite-like (SOD-like) zeolite topologies have been successfully synthesized by introducing an appropriate amount of CO3(2-) from NaCO3 or atmospheric carbon dioxide as a template. Single-crystal X-ray diffraction reveals that the structure consists of the RE3(OH)6(3+) cationic framework with a SOD-like topology built from vertex-sharing [RE4(μ3-OH)4] cubes. The CO3(2-) anions seal the 6-ring opening and Cl(-) anions situated in the channels to achieve charge balance. After calcination at 370 °C, the compound RE3(OH)6(CO3)Cl in situ transforms into a new phase formulated as RE3O4Cl. Interestingly, the structure of RE3O4Cl represents a new SOD-like open framework, associated with the removal of the CO3(2-) from RE3(OH)6(CO3)Cl. The samples are characterized by thermogravimetric analysis (TGA), elemental analysis, X-ray photoelectron spectroscopy and magnetic studies. Furthermore, single-molecule magnet behaviours can be observed for the diluted samples of Dy0.0068Y2.9932(OH)6(CO3)Cl and Dy0.0068Y2.9932O4Cl with a Dy/Y molar ratio of up to 1/440 as well as Er0.19Y2.81(OH)6(CO3)Cl with an Er/Y ratio of 1/15, showing dominant single-ion effects.

First tetrazole-bridged d–f heterometallic MOFs with a large magnetic entropy change

The first example of tetrazole-bridged 3d–4f heterometallic MOFs {(H₃O)₃[Gd₃Mn₂(Trz)₄]·12H₂O}_n was obtained, exhibiting a large magnetic entropy change.

Organically templated linear metal sulfites

Six novel organically-templated linear metal sulfite coordination polymers based on Zn(ii) and Mn(ii) ions are synthesized using different amines and the role of H-bonding to provide structures with increased dimensionalities are discussed.

Three novel polyoxoanion-supported compounds: confinement of polyoxoanions in Ni-containing rigid concave surfaces with enhanced NLO properties

Three new polyoxometalates confined in metal-containing rigid concave surfaces were developed. All of them gave a strong third-order NLO response.