Transition Metal Coordination Polymers with Trans-1,4-Cyclohexanedicarboxylate: Acidity-Controlled Synthesis, Structures and Properties

Diamondoid Ni(II) Coordination Polymer as an Electrocatalyst for Hydrogen and Oxygen Evolution Reactions and Overall Water Splitting

We have successfully synthesized a new Ni(II)-based coordination polymer (CP) [Ni2(cis-1,4-chdc)2(4,4'-bpy)3(H2O)2] (1); (cis-1,4- H2chdc=cis-1,4-cyclohexanedicarboxylic acid and 4,4'-bpy=4,4'-bipyridine) employing slow diffusion method in a single pot technique. The connectivity of Ni(II) ions and bridging cis-1,4-chdc ligand gives rise to a three-dimensional (3D) framework with 2-fold interpenetrated diamondoid topology. Interestingly, the synthesized CP acts as efficient catalyst for electrocatalytic water splitting. The water oxidation activity of compound 1 exhibits Tafel slope equivalent to 361.48 mV.dec-1 for hydrogen evolution reaction (HER) and 353.53 mV.dec-1 for oxygen evolution reaction (OER) in an alkaline medium while almost similar values of Tafel slope for HER and OER equivalent to 287.33 mV.dec-1 and 289.93 mV.dec-1 respectively in acidic medium. Thus, the compound 1 has excellent efficacy in catalyzing HER and OER in acidic as well as alkaline medium, which is ascribed to its distinctive 3D architecture.

Ultrasound-Assisted Metal-Free Synthesis of Functionalized 1,2-Teraryls by Ring Transformation Methodology

The function of styryl acetate as a carbanion nucleophile source has been explored in the ring transformation reaction of 2H-pyranones. The ultrasound assisted carbanion induced ring transformation of 4-amino-6-aryl-3-cyano-2H-pyran-2-ones using (E)-styryl acetate in the presence of KOH and DMF at room temperature is presented as an alternative strategy for the synthesis of functionalized 1,2-teraryls in high yields. This metal-free methodology provides easy access to a series of 1,2-teraryls and features broad functional group tolerance and mild reaction condition. Single crystal X-ray diffraction analysis of 4-(piperidin-1-yl)-6-(thiophen-2-yl)-[1,1'-biphenyl]-3-carbonitrile indicated that the crystal belongs to monoclinic system with a P21 space group having twisted aryl rings.

New Coordination Polymers of Selected Lanthanides with 1,2-Phenylenediacetate Linker: Structures, Thermal and Luminescence Properties

Solvothermal reactions of lanthanide (III) salts with 1,2-phenylenediacetic acid in N,N'-dimethylformamide (DMF) solvent lead to the formation of the metal complexes of the general formula Ln₂(1,2-pda)₃(DMF)₂, where Ln(III) = Pr(1), Sm(2), Eu(3), Tb(4), Dy(5), and Er(6), 1,2-pda = [C₆H₄(CH₂COO)₂]^2-. The compounds were characterized by elemental analysis, powder and single-crystal X-ray diffraction methods, thermal analysis methods (TG-DSC and TG-FTIR), infrared and luminescence spectroscopy. They exhibit structural similarity in the two groups (Pr, Sm, and Eu; Tb, Dy, and Er), which was reflected in their thermal behaviours and spectroscopic properties. Single-crystal X-ray diffraction studies reveal that Sm(2) and Eu(3) complexes form 2D coordination polymers with four crystallographically independent metal centers. Every second lanthanide ion is additionally coordinated by two DMF molecules. The 1,2-phenylenediacetate linker shows different denticity being: penta- and hexadentate while carboxylate groups exhibit bidentate-bridging, bidentate-chelating, and three-dentate bridging-chelating modes. The infrared spectra reflect divergence between these two groups of complexes. The complexes of lighter lanthanides contain in the structure coordinated DMF molecules, while in the structures of heavier complexes, DMF molecules appear in the inner and outer coordination sphere. Both carboxylate groups are deprotonated and engaged in the coordination of metal centers but in different ways in such groups of complexes. In the groups, the thermal decomposition of the isostructural complexes occurs similarly. Pyrolysis of complexes takes place with the formation of such gaseous products as DMF, carbon oxides, ortho-xylene, ethers, water, carboxylic acids, and esters. The complexes of Eu and Tb exhibit characteristic luminescence in the VIS region, while the erbium complex emits NIR wavelength.

Cinnamal Sensing and Luminescence Color Tuning in a Series of Rare-Earth Metal-Organic Frameworks with Trans-1,4-cyclohexanedicarboxylate

Three isostructural metal-organic frameworks ([Ln2(phen)2(NO3)2(chdc)2]·2DMF (Ln3+ = Y3+ for 1, Eu3+ for 2 or Tb3+ for 3; phen = 1,10-phenanthroline; H2chdc = trans-1,4-cyclohexanedicarboxylic acid) were synthesized and characterized. The compounds are based on a binuclear block {M2(phen)2(NO3)2(OOCR)4} assembled into a two-dime nsional square-grid network containing tetragonal channels with 26% total solvent-accessible volume. Yttrium (1)-, europium (2)- and terbium (3)-based structures emit in the blue, red and green regions, respectively, representing the basic colors of the standard RGB matrix. A doping of Eu3+ and/or Tb3+ centers into the Y3+-based phase led to mixed-metal compositions with tunable emission color and high quantum yields (QY) up to 84%. The bright luminescence of a suspension of microcrystalline 3 in DMF (QY = 78%) is effectively quenched by diluted cinnamaldehyde (cinnamal) solutions at millimolar concentrations, suggesting a convenient and analytically viable sensing method for this important chemical.

Intense multi-colored luminescence in a series of rare-earth metal-organic frameworks with aliphatic linkers

Two series of highly luminescent yttrium(iii), europium(iii) and terbium(iii) metal-organic frameworks containing diimine aromatic ligands and the dicarboxylate linker trans-1,4-cyclohexanedicarboxylate (chdc^2-) which can be described by the general formulas [M₂(bpy)₂(chdc)₃], where M = Y³⁺ (1), Eu³⁺ (2), and Tb³⁺ (3) and bpy = 2,2'-bipyridyl, and [M₂(phen)₂(chdc)₃], where M = Y³⁺ (4), Eu³⁺ (5), and Tb³⁺ (6) and phen = 1,10-phenanthroline, were synthesized and characterized. All compounds are based on the same dinuclear {M₂(L)₂(OOCR)₆} building blocks and possess a similar topology of the 3D framework with narrow pores. The chelate aromatic ligands act as efficient light-harvesting antennas for subsequent energy transfer to the emitting metal center (M = Eu³⁺, Tb³⁺) or intraligand photoemission (M = Y³⁺). As a result, the reported compounds display intense emission in the red (Eu³⁺), green (Tb³⁺) or blue (Y³⁺) regions representing three basic colors (RGB) of visible light. The measured quantum yields (QYs) of the solid-state luminescence for individual compounds were found to be 63% (1), 46% (2), 59% (3), 2.3% (4), 55% (5) and 49% (6). The drastic reduction of the luminescence efficiency for 4 is explained by the strong disorder of phen ligands. The high thermal stability (up to 300 °C) and exceptional moisture resistance of the bpy-based frameworks 1-3 were confirmed by TG and PXRD measurements. Various bimetal or trimetal compositions were also prepared for the bpy-series. The luminescence properties of these mixed-metal compounds depend on both the chemical composition and excitation wavelength (λ_ex). Remarkably, pure white emission with color temperature = 6126 K was achieved for [Y_1.68Eu_0.08Tb_0.24(bpy)₂(chdc)₃] at λ_ex = 360 nm with QY = 20%. The reported results suggest that the obtained coordination framework series is a convenient platform for the design of highly efficient light emitting materials with tunable properties.