Polymorphism and Its Influence on Catalytic Activities of Lanthanide-Glutamate-Oxalate Coordination Polymers

To study the relationship between polymorphism and catalytic activities of lanthanide coordination polymers in the cycloaddition reactions of CO2 with epoxides, the monoclinic and triclinic polymorphs of [LnIII(NH3-Glu)(ox)]·2H2O, where LnIII = LaIII (I), PrIII (II), NdIII (III), SmIII (IV), EuIII (V), GdIII (VI), TbIII (VII), and DyIII (VIII), NH3-Glu- = NH3+ containing glutamate, and ox2- = oxalate, were synthesized and characterized. Factors determining polymorphic preference, the discrepancy between the two polymorphic framework structures, potential acidic and basic sites, thermal and chemical stabilities, active surface areas, void volumes, CO2 sorption/desorption isotherms, and temperature-programmed desorption of NH3 and CO2 are comparatively presented. Based on the cycloaddition of CO2 with epichlorohydrin in the presence of tetrabutylammonium bromide under solvent-free conditions and ambient pressure, catalytic activities of the two polymorphs were evaluated, and the relationship between polymorphism and catalytic performances has been established. Better performances of the monoclinic catalysts have been revealed and rationalized. In addition, the scope of monosubstituted epoxides was experimented and the outstanding performance of the monoclinic catalyst in the cycloaddition reaction of CO2 with allyl glycidyl ether under ambient pressure has been disclosed.

Blue-Emitting Ligand-Mediated Assembly of Rare-Earth MOFs toward White-Light Emission, Sensing, Magnetic, and Catalytic Studies

New lanthanide carboxylate compounds with two- (2D) and three-dimensional (3D) structures have been prepared by employing 2,5-bis(prop-2-yn-1-yloxy)terephthalic acid (2,5-BPTA) as an organic linker. The compounds, [Ln(C₁₄H₈O₆)(C₇O₃H₄)·2H₂O]·4(H₂O), Ln = Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy and [Ln(C₇O₃H₄)₃·(C₃H₇ON)·(H₂O)]·2(H₂O)(C₃H₇NO), Ln = La, Ce, Pr, have two- and three-dimensional structures, respectively. In all compounds, lanthanide ions are connected together, forming a dimer, which is connected by the 2,5-BPTA ligand. In the two-dimensional structure, there are two 2,5-BPTA moieties present, and in the three-dimensional structure, there are three 2,5-BPTA moieties present. The lanthanide centers are nine-coordinated, the 2D structure has a tricapped trigonal prismatic arrangement, and the 3D structure has a monocapped distorted square antiprismatic arrangement. The Pr compound forms in both 2D and 3D structures, whose formation depends on the time of the reaction (2 days─2D and 5-6 days─3D). The ligand emits in the blue region, and using the characteristic emission of Eu³⁺ (red) and Tb³⁺ (green) ions, we achieve white light emission in the (Y_0.96Tb_0.02Eu_0.02) compound. The overall quantum yield for the white light emission is 28%. The strong green luminescence of the Tb³⁺-containing compound was employed to selectively sense the Cr³⁺ and Fe³⁺ ions in aqueous solution with limits of detection (LODs) at 0.41 and 8.6 ppm, respectively. The Tb compound was found to be a good heterogeneous catalyst for the Ullman-type O-arylation reaction between phenol and bromoarene with yields of 95%. Magnetic studies on the Gd-, Tb-, and Dy-containing compounds showed weak exchange interactions within the dimeric Ln₂ units. The present work demonstrates the many utilities of the rare-earth-containing MOFs, especially toward white-light emission, metal-ion sensing, and heterogeneous catalysis.

Probing Optical Anisotropy and Polymorph-Dependent Photoluminescence in [Ln2 ] Complexes by Hyperspectral Imaging on Single Crystals

Two homodinuclear and one heterodinuclear lanthanide (Ln)-based complexes of the general formula [Ln₂ (bpm)(tfaa)₆ ] (Ln=Eu (1), Tb (2), Eu-Tb (3), bpm=2,2'-bipyrimidine, tfaa^- =1,1,1-trifluoroacetylacetonate) were synthesized and characterized by single-crystal photoluminescence spectroscopy and hyperspectral imaging. Complexes 1 and 2 crystallize in two polymorphic structures, while three polymorphs were isolated for 3, namely having needle-, plate-, and block-like morphologies. Single-crystal photoluminescence spectroscopy and imaging on Eu³⁺ -containing 1 and 3 revealed polymorph-dependent J-splitting of the hypersensitive ⁵ D₀ →⁷ F₂ Eu³⁺ transition as well as electric-to-magnetic dipole emission intensity ratios. According to these observations, the lowest symmetry chemical environment was attributed to the Eu³⁺ ions present in the needle-like polymorph, also in agreement with single-crystal X-ray diffraction analysis. More importantly, hyperspectral imaging on all three single-crystal polymorphs of 3 exhibits optical anisotropy with photoluminescence enhancement at specific crystallographic faces. This behavior was ascribed to the distinct molecular packing of the Ln-Ln dimers in each polymorphic crystal as well as to face-specific local symmetry of the Eu³⁺ centers. Overall, opto-structural relationships of three Ln-Ln dimers and their single-crystal polymorphs were established as a particularly promising avenue for control of photoluminescence by chemical crystal engineering.

Synthesis of glycerol carbonate over a 2D coordination polymer built with Nd3+ions and organic ligands

The production of glycerol carbonate from glycerol and urea using a 2D coordination polymer as the heterogeneous catalyst.

Activation performance and mechanism of a novel heterogeneous persulfate catalyst: Metal Organic Framework MIL-53(Fe) with FeII/FeIII mixed-valence coordinative unsaturated iron center

In this work, a novel effective heterogeneous catalyst metal-organic framework MIL-53(Fe) has been synthesized for the purpose of activating persulfate (PS). Catalytic performance of MIL-53(Fe) activated under different vacuum conditions was investigated; stability and reusability of the catalyst were evaluated, and the activation mechanism was also investigated. The results indicated that vacuum activation could cause variation of the Fe^II/Fe^III relative amount ratio of the catalyst, and thus would change the catalytic activities of MIL-53(Fe), because Fe^II or Fe^III CUS (coordinative unsaturated metal site) are alternative active sites. It was found that MIL-53(Fe)-2 exhibits good performance for PS activation and could be used for multiple cycles. A removal rate of 98% for Orange G was obtained within 120min (95.7% mineralization efficiency), and 94.3% was attained in the fifth cycle. The mechanism of the activation of PS by MIL-53(Fe) was also suggested, which involves a predominant heterogeneous reaction and an auxiliary homogeneous reaction. The findings of this study provide new insight into the application of the reactive metal-organic frameworks in activating persulfate for the degradation of environmental contaminants.

Tuning the structure, dimensionality and luminescent properties of lanthanide metal–organic frameworks under ancillary ligand influence

Characterization and optical properties of a 1D coordination polymer and 2D and 3D Metal–Organic Frameworks obtained from lanthanide metals, 3-hydroxinaftalene-2,7-disulfonic acid.

Layered exfoliable crystalline materials based on Sm-, Eu- and Eu/Gd-2-phenylsuccinate frameworks. Crystal structure, topology and luminescence properties

New layered 2D MOFs based on 2-phenylsuccinate, Sm, Eu and Eu/Gd are a suitable platform for obtaining exfoliatable frameworks with luminescence properties for potential applications as thin films.

Mutual transformation between crystalline phases and dielectric properties of coordination polymers with the formula [Cd(N-methylimidazole)2(H2O)x(glutarate)]·nH2O (x = 0 or 1; n = 0 or 4)

Two pseudo-polymorphs obtained through controlling the crystallization temperature are mutual transformable via absorbing or losing water.