Preparation and Characterization of a Coordination Polymer Based on Iron (III)-Cyamelurate as a Superior Catalyst for Heterogeneous Fenton-Like Processes

We report on a new iron (iii)-cyamelurate-based coordination polymer. The new material based on a heptazine derivative was prepared in aqueous medium and characterized by a variety of techniques including TGA, FTIR, XRD, HRTEM, and STEM. Due to the high structural stability of the complex in aqueous media, its heterogeneous Fenton-like catalytic activity was evaluated using a model molecule. The results obtained showed a high catalytic activity in both in basic and acid media. The pseudo-first-order rate constants normalized by iron(III) concentrations was approximately 1000 times higher than the result obtained for traditional heterogeneous catalysts based on iron(III) oxyhydroxides. The best observed catalytic activities were attributed to the increase in the binding sites of Fe³⁺ ions, in parallel with the increased exposure of the catalytic sites, leading to a higher atomic efficiency of the reaction.

S-Heptazine N-ligand based luminescent coordination materials: synthesis, structural and luminescent studies of lanthanide-cyamelurate networks

Various series of lanthanide metal-organic networks denoted Ln-Cy (Ln = La, Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb), were synthesized under solvothermal conditions using potassium cyamelurate (K₃Cy) and lanthanide nitrate salts. All obtained materials were fully characterized, and their crystal structures were solved by single-crystal X-ray diffraction. Four types of coordination modes were elucidated for the Ln-Cy series with different Ln³⁺ coordination geometries. Structural studies were performed to compare the various coordination compounds of the Ln-Cy series. Moreover, the cyamelurate linkers of rich π-conjugated and uncoordinated Lewis basic sites were used as an absorbing chromophore to enhance the luminescence quantum efficiency, the band emission and the luminescence lifetime of the coordinated Ln metal centers. Solid-state UV-visible measurements combined with density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations were performed to further explore luminescent features of the Ln-Cy series and their origins.

Exploring Reversible Thermochromic Behavior in a Rare Ni(II)-MOF System

Thermochromic metal-organic frameworks (MOFs) are promising functional materials for a wide range of applications due to their ability to exhibit color variation under external temperature stimuli, yet the development of them with high cyclability and efficient regeneration processes remains challenging. Here, presented is a rare example of an ultrastable Ni(II)-MOF exhibiting an unprecedented reversible four-step color change between two complementary colors in a wide temperature range, which could be repeated for at least 500 cycles without losing crystallinity and thermochromic performance. Notably, the regeneration can be achieved within 1 min by simply letting the crystals cool naturally in the air, facilitated by the unique nature of the channels' inner surface. The reversible thermochromic behavior is owing to a series of reversible crystal structure changes with temperature, including the stepwise dehydration/rehydration process, and structural changes. This work facilitates the future development of more MOF-based reversible thermochromic materials with excellent performance and improved practical applicability.

State of the Art in the Preparation and Properties of Molecular Monomeric s-Heptazines: Syntheses, Characteristics, and Functional Applications

This review gives an account on the fast expanding field of monomeric (or molecular) heptazines, at the exclusion of their various polymeric forms, often referred to as carbon nitrides. While examples of monomeric heptazines were extremely limited until the beginning of this century, the field has started expanding quickly since then, as has the number of reports on polymeric materials, though previous reviews did not separate these fields. We provide here a detailed report on the synthetic procedures for molecular heptazines. We also extensively report on the different achievements realized from these new molecules, in the fields of physical chemistry, spectroscopy, materials preparation, (photo)catalysis, and devices. After a comprehensive summary and discussion on heptazines syntheses and characteristics, we show that starting from well-defined molecules allows a versatility of approaches and a wide tunability of the expected properties. It comes out that the field of monomeric heptazines is now emerging and possibly heading toward maturity, while diverging from the one of polymeric carbon nitrides. It is likely that this area of research will quickly surge to the forefront of the search for active organic molecules, with special attention to the domains of catalysis and organic-based functional materials and devices.

A Rational Design of Microporous Nitrogen-Rich Lanthanide Metal-Organic Frameworks for CO2/CH4 Separation

Three new lanthanide metal-organic frameworks IRHs-(1-3) supported by cyamelurate linkers have been synthesized and structurally characterized. The incorporation of numerous heteroatoms (N and O) into the pore walls and the relatively small microchannels of these porous solids enhance bonding force of the host-guest interactions, thus promoting the adsorption of carbon dioxide (CO₂) over methane (CH₄). The nonpolar covalent bonds in methane also favor the less uptake due to the hydrophilic walls of these frameworks. Grand canonical Monte Carlo simulations were performed to determine the origin of the adsorption. The density isocontour surfaces show that CO₂ is mainly adsorbed on the walls composed of organic linkers and around the metal sites, whereas no specific adsorption site is observed for CH₄, which indicates weak interactions between the framework and the adsorbed gas. As expected, the simulations show that CH₄ is not observed around the metal center due to the presence of H₂O molecules. The excellent selectivity of CO₂/CH₄ binary mixture was predicted by the ideal adsorbed solution theory (IAST) via correlating pure component adsorption isotherms with the Toth model. At 25 °C and 1 bar, the CO₂ and CH₄ uptakes for IRH-3 were 2.7 and 0.07 mol/kg, respectively, and the IAST predicated selectivity for CO₂/CH₄ (1:1) reached 27, which is among the best value for MOF materials.

Intercalated 2D+2D hydrogen-bonded sheets in co-crystals of cobalt salt with 1H,1′H-[3,3′]bipyridinyl-6,6′-dione

Co-crystals of Co(II) salt and 1H,1′H-[3,3′]bipyridinyl-6,6′-dione 1 with the composition 1·Co(CHOO)2(H2O)4 were obtained by mixing both reactants. The single-crystal structure reveals that the metal salt and organic ratio is 1:1. The supramolecular organization of the two components in the co-crystal was mainly dictated by hydrogen bonds between 1 and Co(II) complex. Infrared and powder X-ray diffraction were used to confirm the homogeneity and the phase purity of the bulk crystalline sample of 1·Co(CHOO)2(H2O)4. TGA/DTA was recorded to evaluate the thermal stability of the co-crystals.