A Series of Lanthanide Metal-Organic Frameworks with Interesting Adjustable Photoluminescence Constructed by Helical Chains

A new family of boat-shaped Ln8 clusters exhibiting the magnetocaloric effect and slow magnetic relaxation

Designing and synthesizing lanthanide clusters have always been a research hotspot. Herein, three lanthanide clusters with the formula [Ln₈(IN)₁₄(μ₃-OH)₈(μ₂-OH)₂(H₂O)₈]·xH₂O (Ln = 1-Gd and x = 11; Ln = 2-Dy and x = 8; Ln = 3-Eu and x = 8) have been isolated in the presence of isonicotinic acid under solvothermal conditions. Structural analysis indicates that those three compounds are isostructural, featuring boat-shaped {Ln₈} metal frameworks. Magnetic measurements reveal that 1-Gd exhibits a larger MCE with the maximum -ΔS_m value of 31.77 J kg^-1 K^-1 at 2 K for ΔH = 7 T, while 2-Dy displays slow magnetization relaxation. Besides, the photoluminescence properties of 3-Eu were investigated.

Preparation and characterization of two lanthanide complexes with one-dimensional chain-like structures

Two novel RE–Hg (RE = rare earth) complexes [RE(IA)3(H3O)2]2 n·2 n(HgCl4)· n(HgCl5)· nH2O·3 nH3O (RE = Y, 1; Lu, 2; IA = isonicotinic acid anion) were synthesized through hydrothermal reactions and are structurally characterized by single-crystal X-ray diffraction. The two complexes are isostructures and are characteristic of a one-dimensional chain-like structure. Both complexes are characterized by a three-dimensional supramolecular network. Photoluminescence experiments using solid-state samples show that they possess emission bands in the blue or red region. They have remarkable CIE chromaticity coordinates of (0.1172, 0.182) and (0.623, 0.3765), respectively. As a result, they are potential candidates for light-emitting materials for light-emitting diodes. They show wide optical band gaps of 3.29 eV and 2.89 eV, as revealed by the solid-state UV/Vis diffuse reflectance spectra.

A Series Three-Dimensional Ln4Cr4 (Ln = Gd, Tb, Er) Heterometallic Cluster-Based Coordination Polymers Containing Interesting Nanotubes Exhibiting High Magnetic Entropy

A series of novel 3D 3d-4f heterometallic cluster-based coordination polymers, [Ln₄Cr₄(μ₃-O)₄(μ₄-O)₄(NA)₈(H₂O)₁₂]·xH₂O (Ln = 1-Gd, 2-Tb, 3-Er; HNA = nicotinic acid; x = 13 (1-Gd), 11.33 (2-Tb), 15 (3-Er)), have been successfully synthesized by hydrothermal method using nicotinic acid as bridging ligand. The single-crystal X-ray diffraction (SCXRD) analysis indicated that the basic unit of Ln₄Cr₄ shows a butterfly-shaped structure. Furthermore, each Ln₄Cr₄ cluster connects with other four Ln₄Cr₄ clusters by bridging NA^- ligands to form a 3D structure containing interesting 1D honeycomb-shaped coordination nanotubes. The variable temperature magnetic susceptibility measurements of compound 1 revealed that the existence of antiferromagnetic (AF) coupling between the metal ions in the Gd₄Cr₄ clusters. Field-dependent isothermal magnetization studies displayed that the magnetic entropy change (-ΔS_m) value of 1-Gd reached 22.05 J K^-1 kg^-1.

From IR to x-rays: gaining molecular level insights on metal-organic frameworks through spectroscopy

This topical review focuses on the application of several types of spectroscopy methods to a class of solid state materials called metal organic frameworks (MOFs). MOFs are self-assembled, porous crystalline materials composed of metal cluster nodes linked through coordination bonds with organic or organometallic molecular constituents. Their unique host-guest properties make them attractive for many adsorption-based applications such as gas storage and separation, catalysis, sensing and others. While much research focuses on the development and application of these materials, fundamental studies of MOF properties and molecular level host-guest interactions behind their functionality have become a significant research direction on its own. Spectroscopy methods are now ubiquitous tools in this pursuit. This review focuses on the application of three classes of spectroscopy methods to MOF materials: vibrational, optical electronic and x-ray spectroscopies. Following brief introductions to each method that include pertinent theory and experimental considerations, we present a broad overview of the types of MOF systems that have been studied, with specific examples and important new molecular level insights highlighted along the way. The current status of spectroscopic studies of MOFs is presented at the end along with some perspectives on the future directions in this area of research.

Syntheses of three new isostructural lanthanide coordination polymers with tunable emission colours through bimetallic doping, and their luminescence sensing properties

Tuning the emissive color changes of lanthanide (Ln) complexes is an important and appealing project for promoting the applications of Ln-complexes. A solvothermal reaction of 4-cyano-3-methylbenzoic acid (HL) and Ln(NO3)3·6H2O affords three isostructural Ln-complexes [Eu(L)3(H2O)2]n (1-Ln) (Ln = Eu, Gd and Tb) with one-dimensional chain structures. 1-Eu and 1-Tb show bright red and green emissions with absolute quantum yields of 3.06% and 11.96%, respectively, and the energy transfer was analyzed in detail through combined calculations. Interestingly, a series of heterometallic doped 1-TbxEu1-x coordination polymers were also obtained by mixing different ratios of Eu3+ and Tb3+ ions, which possess continuous luminescent color changes from green to yellow, orange and red. In addition, 1-Eu exhibits high quenching efficiency and low detection limit (∼10-4 M) for the simultaneous sensing of MnO4-, CrO42- and Cr2O72- ions in water.

Unprecedented three-dimensional hydrogen-bonded hex topological chiral lanthanide–organic frameworks built from an achiral ligand

The design and preparation of chiral metal–organic frameworks (CMOFs) from achiral ligands are a big challenge. Using 3-nitro-4-(pyridin-4-yl)benzoic acid (HL) as a new linker, a total of eight chiral lanthanide–organic frameworks (LOFs), namely poly[diaquatris[μ2-3-nitro-4-(pyridin-4-yl)benzoato-κ2 O:O′]lanthanide(III)], L- and D-[Ln(C12H7N2O4)3(H2O)2] n [(1), Ln = Eu; (2), Ln = Gd; (3), Ln = Dy; (4), Ln = Tb], were hydrothermally synthesized without chiral reagents and determined by X-ray crystallography. Crystal structure analyses show that L-(1)–(4) crystallize in the hexagonal P65 space group and are isomorphous and isostructural, while the enantiomers D-(1)–(4) crystallize in the hexagonal P61 space group. All LnIII ions are octacoordinated by six carboxyl O atoms of six 3-nitro-4-(pyridin-4-yl)benzoate ligands and two water molecules in a dodecahedral geometry. A one-dimensional neutral helical [Ln2(CO2)3] n chain is observed in (1)–(4) as a chiral origin. These helical chains are further interconnected via directional hydrogen-bonding interactions between pyridyl groups and water molecules to construct a three-dimensional (3D) homochiral network with hex topology. The present CMOF structure is the first chiral 3D hydrogen-bonded hex-net and shows good water stability. Solid-state circular dichroism (CD) signals revealed that (1)–(4) crystallized through spontaneous resolution. Furthermore, (1) and (4) display a strong red and green photoluminescence at room temperature, respectively, but their intensities reduce to almost half at 200 °C. Notably, upon excitation under visible light (463 nm), a circularly polarized luminescence (CPL) of (1) in the solid state is observed for the first time, with a g lum value of 2.61 × 10−2.

Slow relaxation of magnetization and luminescence properties of a novel dysprosium and pyrene-1,3,6,8-tetrasulfonate based MOF

A novel multifunctional Dy(iii) and pyrene-1,3,6,8-tetrasulfonate based MOF displays intense PL/ SIM behaviour.

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.

Synthesis, Structures and Luminescence Properties of Metal-Organic Frameworks Based on Lithium-Lanthanide and Terephthalate

Metal-organic frameworks assembled from Ln(III), Li(I) and rigid dicarboxylate ligand, formulated as [LiLn(BDC)₂(H₂O)·2(H₂O)] (MS1-6,7a) and [LiTb(BDC)₂] (MS7b) (Ln = Tb, Dy, Ho, Er, Yb, Y_0.96Eu_0.04, Y_0.93Tb_0.07, and H₂BDC = terephthalic acid), were obtained under hydrothermal conditions. The isostructural MS1-6 crystallize in monoclinic P2₁/c space group. While, in the case of Tb³⁺ a mixture of at least two phases was obtained, the former one (MS7a) and a new monoclinic C2/c phase (MS7b). All compounds have been studied by single-crystal and powder X-ray diffraction, thermal analyses (TGA), vibrational spectroscopy (FTIR), and scanning electron microscopy (SEM-EDX). The structures of MS1-6 and MS7a are built up of inorganic-organic hybrid chains. These chains constructed from unusual four-membered rings, are formed by edge- and vertex-shared {LnO₈} and {LiO₄} polyhedra through oxygen atoms O3 (vertex) and O6-O7 (edge). Each chain is cross-linked to six neighboring chains through six terephthalate bridges. While, the structure of MS7b is constructed from double inorganic chains, and each chain is, in turn, related symmetrically to the adjacent one through the c glide plane. These chains are formed by infinitely alternating {LiO₄} and {TbO₈} polyhedra through (O2-O3) edges to create Tb–O–Li connectivity along the c-axis. Both MS1-6,7a and MS7b structures possess a 3D framework with 1D trigonal channels running along the a and c axes, containing water molecules and anhydrous, respectively. Topological studies revealed that MS1-6 and MS7a have a new 2-nodal 3,10-c net, while MS7b generates a 3D net with unusual β-Sn topology. The photoluminescence properties Eu- and Tb-doped compounds (MS5-6) are also investigated, exhibiting strong red and green light emissions, respectively, which are attributed to the efficient energy transfer process from the BDC ligand to Eu³⁺ and Tb³⁺.