Tuning of the Network Dimensionality and Photoluminescent Properties in Homo- and Heteroleptic Lanthanide Coordination Polymers

The crystal structure of catena-[nitrato-κ 2 O,O′-(μ 3-3-iodobenzene-1,2-dicarboxylato-κ 4 O:O′:O″,O‴)-(2,2′:6′,2″-terpyridine-κ 3 N,N′,N″)lanthanum(III)], C23H14IN4O7La

C23H14IN4O7La, triclinic, P 1 ‾ $P\overline{1}$ (no. 2), a = 8.2438(3) Å, b = 12.3786(5) Å, c = 12.6230(5) Å, α = 111.802(1)°, β = 91.144(1)°, γ = 100.6470(10)°, V = 1169.86(8) Å3, Z = 2, R gt(F) = 0.0313, wR ref(F 2) = 0.1051, T = 296 K.

Metal-Organic Framework vs. Coordination Polymer—Influence of the Lanthanide on the Nature of the Heteroleptic Anilate/Terephtalate 3D Network

Metal-organic frameworks (MOFs), whose definition has been regularly debated, are a sub-class of coordination polymers (CPs) which may feature both an overall 3D architecture and some degree of porosity. In this context, MOFs based on lanthanides (Ln-MOFs) could find many applications due to the combination of sorption properties and magnetic/luminescent behaviors. Here we report rare examples of 3D Ln-CPs based on anilate linkers, obtained under solvothermal conditions using a heteroleptic strategy. The three compounds of formula [Yb2(μ-ClCNAn)2(μ-F4BDC)(H2O)4]·(H2O)3 (1), [Er2(μ-ClCNAn)2(μ-F4BDC)(H2O)4]·(H2O)4 (2) and [Eu2(μ-ClCNAn)2(μ-F4BDC)(H2O)6] (3) have been characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and optical measurements. Structural characterization revealed that compounds 1 and 2 present an interesting MOF architecture with extended rectangular cavities which are only filled with water molecules. On the other hand, compound 3 shows a much more complex topology with no apparent cavities. We discuss here the origins of such differences and highlight the crucial role of the Ln(III) ion nature for the topology of the CP. Compounds 1 and 2 now offer a playground to investigate the possible synergy between gas/solvent sorption and magnetic/luminescent properties of Ln-MOFs.

Turn-up Luminescent Sensing of Ultraviolet Radiation by Lanthanide Metal-Organic Frameworks

Here, we report a series of two-dimensional lanthanide metal-organic frameworks Ln-DBTPA (where DBTPA = 2,5-dibromoterephthalic acid and Ln = Tb (1), Eu (2), or Gd (3)) showing a unique turn-up responsiveness toward ultraviolet (UV) radiation. The luminescence enhancement was derived from the accumulated radicals that can promote the intersystem crossing process. The compound 1 shows an ultralow detection limit of 9.1 × 10^-9 J toward UV radiation, representing a new type of luminescent UV detectors.

Emergence of Thorium-Based Polyoxo Clusters as a Platform for Selective X-ray Dosimetry

A brand-new application of thorium-bearing clusters in the field of ionizing radiation detection is exemplified by two novel hexanuclear thorium clusters, Th-bppCOO-1 and Th-bppCOO-2, which incorporate carboxylate-functionalized 2,6-di(pyrazol-1-yl)pyridine ligands. Notably, Th-bppCOO-1 is composed of an unprecedented [Th₆(OH)₄O₄(H₂O)₅]¹²⁺ secondary building unit, the Th₆ core of which is decorated by five H₂O molecules. Furthermore, selective photoluminescence quenching responses of Th-bppCOO-1 and Th-bppCOO-2 toward X-ray over UV radiation have been demonstrated for the first time.

Combined Experimental/Theoretical Study on the Luminescent Properties of Homoleptic/Heteroleptic Erbium(III) Anilate-Based 2D Coordination Polymers

The synthesis, structural and photophysical characterization, and theoretical studies on homo/heteroleptic neutral 2D-layered coordination polymers (CPs), obtained by combining the Er^III ion with chlorocyananilate (ClCNAn) and/or tetrafluoroterephthalate (F₄BDC) linkers, are herein reported. The structure of the heteroleptic Er^III-based CP, formulated as [Er₂(ClCNAn)₂(F₄BDC)(DMSO)₆]_n (1) is also reported. 1 crystallizes in the triclinic P1̅ space group, and the structure consists of neutral 2D layers formed by Er^III ions linked through the two linkers oriented in such a way that the neighboring 2D layers are eclipsed along the a axis, leading to parallelogram-like cavities. Photophysical measurements highlight the prominent role of chlorocyananilate linkers as optical antennas toward lanthanide ions, while wave-function-theory analysis supports the experimental findings, providing evidence for the effect of ligand substitution on the luminescence properties of homo/heteroleptic 2D CPs.

Achieving colour tuneable and white-light luminescence in a large family of dual-emission lanthanide coordination polymers

Expanding the family of lanthanide terpyridine coordination polymers has yielded eighteen new complexes with two different phases, Ln(TPC)₂(HCOO)(H₂O) (Ln-1) and Ln(TPC)(HCOO)₂ (Ln-2) (Ln = Sm-Lu, except Tm). Both structures are composed of lanthanide cations interconnected by 2,2':6',2''-terpyridine-4'-carboxylate ligands to yield one-dimensional chain topologies. However, the incorporation of an additional crystallographically unique decorative TPC ligand into Ln-1 gives rises to a distinct phase. The encapsulation of both metal- and ligand-based phosphors within single coordination polymers leads to dual-emission of the afforded materials. Furthermore, judicious lanthanide doping in heterometallic Ln-1 and Ln-2 allows for fine-tuning the photoluminescent colours over a wide range of gamut. Such a combination showcases the capability to fine-tune the emission colours from deep green, to red, and to blue. In addition, direct white-light emission upon UV excitation can be achieved in the Sm_xGd_1-x-1 system.

The coordination chemistry of benzhydrazide with lanthanide(iii) ions: hydrothermal in situ ligand formation, structures, magnetic and photoluminescence sensing properties

The influence of synthetic conditions on the solid-state structural formation of lanthanide(iii) complexes based on a hydrazide ligand have been investigated and reported. Depending on the solvents and reaction temperatures, the reactions of hydrated Ln(NO3)3 with a benzohydrazide (bzz) ligand afforded three classes of lanthanide(iii) coordination complexes viz. [Ln(bzz)(NO3)](NO3)2 (1Ln; Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5)), [Ln(bzz)(ben)3(H2O)]·H2O (2Ln; Ln = Pr (6), Nd (7), Sm (8), Eu (9), Gd (10), Tb (11), Dy (12), Er (13)), and [Ln3(ben)3] (3Ln; Ln = Eu (14), Gd (15), Tb (16), Dy (17), Er (18), Tm (19), Yb (20), Lu (21)). Complexes 1-5 in series 1Ln were isolated by slow evaporation of their isopropanol solutions at ambient temperature, and the complexes display similar discrete structures bearing distinct intermolecular N-H⋯O hydrogen bonds to generate a three-dimensional (3D) supramolecular architecture. Complexes 6-13 in series 2Ln were obtained under hydrothermal conditions at 110 °C where the in situ generated benzoate (ben) ligands participated in the formation of one-dimensional (1D) coordination polymers (CPs) with the bzz ligands. At a temperature of 145 °C the hydrothermal conditions result in the formation of the thermodynamically more stable products of 14-21 in series 3Ln, in which the bzz ligand underwent complete in situ hydrolysis to create the ben ligand. These coordination assemblies feature 1D zigzag chains that are formed by unusual low coordination numbers of the six- and seven-fold coordinated Ln3+ centers bridged by the ben ligands in μ 2- and μ 3-coordination modes. Notably, the chain structures of 2Ln can be transformed into the zigzag tape-like structures of 3Ln upon heating the crystalline samples to 400 °C in air. In the solid state at room temperature, the Eu- (2, 9, 14) and Tb- (4, 11, 16) containing complexes emit red and green light, respectively. The luminescence investigations show that the Eu- (9, 14) and Tb-(11, 16) based CPs could be used as fluorescent probes for acetone and Co2+ ions via an energy competition mechanism. Meanwhile, the Gd- (10, 15) and Dy- (12, 17) based CPs show typical antiferromagnetic interactions.

Structure-Property Relationships in Photoluminescent Bismuth Halide Organic Hybrid Materials

Seven novel bismuth(III)-halide phases, Bi₂Cl₆(terpy)₂·0.5(H₂O) (1), Bi₂Cl₄(terpy)₂(k₂-TC)₂(2) (TC = 2-thiophene monocarboxylate), BiCl(terpy)(k₂-TC)₂ (3A-Cl), BiBr(terpy)(k₂-TC)₂ (3A-Br), BiCl(terpy)(k₂-TC)₂ (3B-Cl), [BiCl(terpy)(k₂-TC)₂][Bi(terpy)(k₂-TC)₃]·0.55(TCA) (4), [BiBr₃(terpy)(MeOH)] (5), and [BiBr₂(terpy)(k₂-TC)][BiBr_1.16(terpy)(k₂-TC)_1.84] (6), were prepared under mild synthetic conditions from methanolic/aqueous solutions containing BiX₃ (X = Cl, Br) and 2,2':6',2″-terpyridine (terpy) and/or 2-thiophene monocarboxylic acid (TCA). A heterometallic series, 3A-Bi_1-xEu_xCl, with the general formula Bi_1-xEu_xCl(terpy)(k₂-TC)₂ (x = 0.001, 0.005, 0.01, 0.05) was also prepared through trace Eu doping of the 3A-Cl phase. The structures were determined through single-crystal X-ray diffraction and are built from a range of molecular units including monomeric and dimeric complexes. The solid-state photoluminescent properties of the compounds were examined through steady-state and time-resolved methods. While the homometallic phases exhibited broad green to yellow emission, the heterometallic phases displayed yellow, orange, and red emission that can be attributed to the simultaneous ligand/Bi-halide and Eu centered emissions. Photoluminescent color tuning was achieved by controlling the relative intensities of these concurrent emissions through compositional modifications including the Eu doping percentage. Notably, all emissive homo- and heterometallic phases exhibited rare visible excitation pathways that based on theoretical quantum mechanical calculations are attributed to halide-metal to ligand charge transfer (XMLCT). Through a combined experimental and computational approach, fundamental insight into the structure-property relationships within these Bi halide organic hybrid materials is provided.