A new mode of luminescence in lanthanide oxalates metal–organic frameworks

Two lanthanide metal–organic frameworks [Ln-MOFs, Ln = Eu(III), Tb(III)] composed of oxalic acid and Ln building units were hydrothermally synthesized and fully characterized by powder X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscope, and energy-dispersive X-ray spectroscopy. Furthermore, their magnetic susceptibility measurements were obtained using SQUID based vibrating sample magnetometer (MPMS 3, Quantum Design). Both Ln-MOFs exhibited highly efficient luminescent property. Solid-state photoluminescence (PL) measurements revealed phosphorescence emission bands of Eu-MOF and Tb-MOF centered at 618 nm (red emission) and 550 nm (green emission) upon excitation at 396 nm and 285 nm, respectively. Eu-MOF and Tb-MOF displayed a phosphorescence quantum yield of 53% and 40%, respectively. Time-resolved PL analyses showed very long lifetime values, at 600 and 1065 ± 1 µs for Eu-MOF and Tb-MOF, respectively. Calculations performed by density functional theory indicated a charge transfer form metal centres to the ligand which was in good agreement with the experimental studies. Therefore, this new mode of highly photoluminescent MOF materials is studied for the first time which paves the way for better understanding of these systems for potential applications.

Alkali and alkaline earth coordination polymers constructed from benzene-1,2,4,5-tetracarboxylic acid and flexible dicarboxylate acid ligands: syntheses, structures and spectroscopic and thermal properties

Two new metal coordination complexes, namely, poly[aqua(μ₆-benzene-1,2,4,5-tetracarboxylic acid-κ⁸O¹:O¹,O²:O^2':O⁴:O⁴,O⁵:O^5')(μ-but-2-enedioato-κ²O¹:O⁴)potassium(I)], [K₂(C₄H₂O₄)(C₁₀H₆O₈)(H₂O)₂]_n or [K₂(fum)(H₄btec)(H₂O)₂]_n, (1), and poly[aqua(μ₈-2,5-dicarboxybenzene-1,4-dicarboxylato-κ¹²O¹:O^1',O²:O²,O^2':O^2':O⁴:O^4',O⁵:O⁵,O^5':O^5')(μ-ethanedioato-κ⁴O¹,O²:O^1',O^2')strontium(II)], [Sr₂(C₂O₄)(C₁₀H₄O₈)(H₂O)₂]_n or [Sr₂(ox)(H₂btec)(H₂O)₂]_n, (2) (H₄btec = benzene-1,2,4,5-tetracarboxylic acid, H₂btec = 2,5-dicarboxybenzene-1,4-dicarboxylate, fum = fumarate and ox = oxalate), have been obtained under hydrothermal conditions by reacting the different alkali and alkaline earth metal salts with H₄btec, fumaric acid (H₂fum) and oxalic acid (H₂ox). Complexes (1) and (2) were structurally characterized by single-crystal X-ray diffraction, IR and UV-Vis spectroscopy, powder X-ray diffraction (PXRD) and thermogravimetic analysis-differential scanning calorimetry (TGA-DSC). Complex (1) displays a two-dimensional (2D) layer with the K⁺ ion in a distorted pentagonal bipyramidal geometry and exhibits a uninodal 6-connected hxl/Shubnikov plane net (3,6) with {3⁶.4⁶.5³} topology. Complex (2) displays a three-dimensional (3D) network structure, in which the Sr²⁺ ion is in a distorted monocapped square antiprism geometry. The framework possess a binodal (5,8)-connected net with the Schläfli symbol {3².4¹⁰.5⁸.6⁴.7⁴}{3².4⁶.5²}₂. The 3D Hirshfeld surfaces and 2D fingerprint plots show that the main interactions are the O...H/H...O intermolecular interactions. Moreover, the thermal decompositions of (1) and (2) in the temperature range 303-1273 K revealed that they both decompose in three steps and transform to the corresponding metal oxide.

Lanthanide complexes based on a conjugated pyridine carboxylate ligand: structures, luminescence and magnetic properties

Three lanthanide compounds have been synthesized, namely, {[Dy₂(bpda)₃(H₂O)₃]₄·2H₂O}(Dy-1), {[Sm(bpda)₂·(H₂O)]·H₂O}_n (Sm-2) and {[Tb₂(bpda)₃(H₂O)₃]₄·2H₂O} (Tb-3) (H₂bpda = 2,2′-bipyridine-6,6′-dicarboxylic acid). Their structures were determined by single crystal X-ray diffraction and characterized by elemental analysis, infrared spectroscopy and thermogravimetric analysis. Dy-1 and Tb-3 are isostructural with a conjugate bimolecular four-nuclear cluster structure constructed with intramolecular hydrogen bonds and they form a 3D supramolecular structure with intermolecular hydrogen bonding. Sm-2 is a one-dimensional chain structure and is further connected by intricate hydrogen bonds into a three-dimensional supramolecular structure. These three compounds exhibit significant characteristic luminescence from the ligand to the central Ln(iii) ion, which is found by solid-state photoluminescence measurement. Sm-2 exhibits a long luminescence lifetime and high fluorescence quantum yield. A slow relaxation phenomenon is observed for the dysprosium compound by measuring the alternating-current susceptibility at low temperature and the underlying mechanism was further confirmed by theoretical calculations.

The structures, fluorescence and magnetic properties of series three lanthanide complexes have been investigated. Dysprosium complex exhibit the single-molecule behavior.

Enhanced luminescence and tunable magnetic properties of lanthanide coordination polymers based on fluorine substitution and phenanthroline ligand

A family of highly stable lanthanide coordination polymers incorporating fluorine-substituted carboxylate tectonics and the rigid ligand phenanthroline, namely, {[Ln m (Tfbda) n (Phen)2·2H2O]·2H2O} z , (Ln = Pr (1), Ho (4) and Gd (7), m = 2, n = 3); {[Ln3 (Tfbda) m 1 (Tfba) m 2 (Phen) n ·2H2O]·H2O} z (z > 1, Ln = Dy (3), Er (5) and Yb (6), m 1 = 4, m 2 = 1, n = 3); [Ln2(H2Tfbda)4(Phen)2·(H2O)2]·Phen (Ln = Nd (2)), Tfbda = 3,4,5,6-tetrafluoro-benzene-1,2-dioic acid, Tfba = 2,3,4,5-tetrafluorobenzoic acid have been afforded under hydrothermal conditions. The series of coordination polymers exhibited diverse structural motifs, from dinuclear cluster to 1-D chain arrary, displaying efficiently sensitized luminescence over a spectral range from visible to near-infrared (NIR) region and a long lifetime, due to efficient energy transfer from fluorine-substituted ligands to Ln(iii) centers in solid state. Slow relaxation magnetization and significant frequency- and temperature-dependent peaks were observed in trinuclear Dy(iii)-based coordination polymer 3. DC magnetic susceptibility studies reveal the existence of weak ferromagnetic interaction within 7.

Stable Lanthanide-Organic Framework Materials Constructed by a Triazolyl Carboxylate Ligand: Multifunction Detection and White Luminescence Tuning

Under hydrothermal conditions, we have successfully synthesized six isostructural lanthanide coordination polymers, [LnL_1.5(H₂O)₂]·1.75H₂O (1-6; Ln = Eu, La, Pr, Nd, Sm, Gd), by the reaction of 5-methyl-1-(4-carboxylphenyl)-1 H-1,2,3-triazole-4-carboxylic acid (H₂L) and Ln(NO₃)₃·6H₂O. Structural analysis shows that polymers 1-6 show novel three-dimensional supramolecular network structures. The luminescent properties for polymer 1 have been investigated at room temperature. The results have shown that polymer 1 can be used as a chemical sensor for multifunctional testing such as UO₂²⁺, Fe³⁺ ion detection, and small organic molecule detection because of its strong fluorescence properties. In particular, polymer 1 exhibits extremely high selectivity and sensitivity for the detection of Fe³⁺ ions. In addition, white-light emission is achieved through a reasonable tuning proportion by mixing Gd³⁺ and Eu³⁺.

Crystal structure of poly[tetraaqua-(μ4-oxalato-κ4 O,O′:O′′,O′′′)-(μ8-benzene-1,2,4,5-tetracarboxylato-κ8 O 1:O 2:O 3:O 4:O 5:O 6:O 7:O 8)yttrium(III)], C6H5O8Y

C6H5O8Y, triclinic, P1̄ (no. 2), a = 6.2090(17) Å, b = 8.573(4) Å, c = 8.863(2) Å, α = 111.018(6)°, β = 109.850(4)°, γ = 91.866(6)°, V = 407.8(2) Å3, Z = 2, R gt(F) = 0.0435, wR ref(F 2) = 0.1332, T = 296(2) K.

Temperature-dependent 3D structures of lanthanide coordination polymers based on dicarboxylate mixed ligands

Four families of fourteen three-dimensional (3D) lanthanide coordination polymers (CPs) with dicarboxylate mixed ligands have been synthesized hydrothermally at different temperatures.

Crystal structure of poly[di-chlorido-(μ-2,5-di-carb-oxy-benzene-1,4-di-carboxyl-ato-κ2O1:O4)bis-[μ-4'-(pyridin-3-yl)-4,2':6',4''-terpyridine-κ2N1:N4']dizinc]

In the title polymeric ZnII complex, [Zn2(C10H4O8)Cl2(C20H14N4)2] n , the ZnII cations are bridged by both 2,5-di-carb-oxy-benzene-1,4-di-carboxyl-ate dianions and 4'-(pyridin-3-yl)-4,2':6',4''-terpyridine ligands, forming ladder-like polymeric chains propagating along [1-10]. The Cl- anion further coordinates the ZnII cation to complete a distorted tetra-hedral environment. In the 4'-(pyridin-3-yl)-4,2':6',4''-terpyridine ligand, the three sideward pyridine rings are twisted with respect to the central pyridine ring by 39.27 (12), 14.89 (13) and 3.36 (13)°, respectively. In the crystal, classical O-H⋯N hydrogen bonds and weak C-H⋯O and C-H⋯Cl hydrogen bonds link the chains into a three-dimensional supra-molecular architecture. π-π stacking is observed between the pyridine and benzene rings of neighbouring polymeric chains, with a centroid-to-centroid distance of 3.7280 (14) Å.

Synthesis, crystal structure, photoluminescence property of a series of 3d-4f coordination supramolecular complexes

A series of 3d-4f heterobinuclear complexes were constructed by employing the 2,2'-bipy (2,2'-bipy=2,2'-bipyridine) ligand and corresponding metal ions (M(II)/Ln(III), M=Co(II), Cu(II) and Zn(II); Ln(III)=Nd(III), Sm(III), Eu(III) and Tb(III)). Elemental analyses, IR, UV-vis-NIR spectra, PXRD and single crystal X-ray diffraction analysis reveal that complexes 1-4, 5-8, and 9-12 are isomorphous, respectively. The zero-dimensional structures are further connected to 2D or 3D supramolecular network structures via extensive intermolecular hydrogen bonds. Luminescence studies for the heterobinuclear complexes containing Sm(III), Eu(III) and Tb(III) reveal that the chromophoric composed of Zn(II)/L may efficiently sensitize the luminescence of the rare earth cations which acts as an antenna, whereas the existence of Cu(II) leads to the quenching of the luminescence of Ln(III) ions.

Syntheses, structures and luminescence of a series of coordination polymers constructed with 4-substituted 1,2,4-triazole and biscarboxylate co-ligands

Eight coordination polymers were hydrothermal synthesized based on semi-rigid 4-substituted 1,2,4-triazole btpm and biscarboxylate ligands. 1–8 show the structural diversity based on mono-metal, bi-, tri- and tetra-nuclear metal clusters.

A microporous lanthanum metal–organic framework as a bi-functional chemosensor for the detection of picric acid and Fe3+ ions

A novel microporous lanthanum metal–organic framework 1 was synthesized by using the rigid unsymmetrical tricarboxylate ligand H₃TPT. This compound exhibits selective detection of picric acid (PA) and Fe³⁺ ion.

Straw-sheaf-like terbium-based coordination polymer architectures: microwave-assisted synthesis and their application as selective luminescent probes for heavy metal ions

Terbium-based coordination polymer architectures were successfully synthesized via a microwave heating approach and they showed highly sensitive and selective luminescence quenching to Pb²⁺ in aqueous solution.

Syntheses, topologies, and luminescence of four Ln–organic polymers constructed from aromatic tetracarboxylic acids

Four interesting Ln coordination polymers based on tetracarboxylate acids have been hydrothermally synthesized through the linker extension strategy.

Three novel d7/d10 metal complexes with N-heterocyclic ligand of 2,6-bis(3-pyrazolyl)pyridine: synthesis, structure, surface photovoltage spectroscopy and photocatalytic activity

We synthesized three novel d⁷/d¹⁰ metal complexes with 2,6-bis(3-pyrazolyl)pyridine and studied their surface photovoltage spectra and photocatalytic activities.