Structural and thermodynamic insights into the coordination preference of norbornadiene with the initiator complex [RuCl2(PPh3)2(piperidine)] in polymerization via olefin metathesis.

The metathesis reaction has been an important tool in both organic and inorganic synthetic chemistry. More specifically in polymer chemistry, ring opening metathesis polymerization (ROMP), via the formation of an active metal-carbene species (MCHR), has been widely used. The elucidation of the mechanism for ROMP opened the way for the development of well-defined catalysts, suited to local conditions. In the present study, we employed density functional theory (DFT) to investigate three reaction pathways for the formation of a species capable of activating ROMP. The active species is formed from the [RuCl2(PPh3)2(pip)] complex in the presence of norbornadiene (NBD) and the carbene source ethyl diazoacetate (EDA). Formation of a hexacoordinated intermediate [RuCl2(PPh3)2(pip)(NBD)] is favored in the first step, with NBD doubly coordinated to the [RuCl2(PPh3)2(pip)] moiety. Analysis of donation (X → Ru) and back-donation (Ru → X) processes in the [RuCl2(PPh3)2(pip)(NBD)] complex shows that piperidine behaves as a σ donor, while NBD behaves as a π donor and the PPh3 groups act as π acceptors. The intensity of the orbital component is predominant in relation to the steric component in the complex. Thus, we propose that the reaction occurs through the formation of a hexacoordinated complex, followed by the dissociation of a PPh3 group, thus forming a complex where NBD is doubly coordinated to the metal center. Coordination of EDA leads finally to the catalyst capable of forming the metallocyclobutane intermediate required for the ROMP reaction.

Structural and Optical Properties of Ca0.9Cu0.01WO4 Solid Solution Synthesized by Sonochemistry Method at Room Temperature.

In this work, we report the room-temperature synthesis of pure calcium tungstate (CaWO4) and copper-doped calcium tungstate solid solution (Ca0.99Cu0.01WO4) by using a sonochemistry method. These materials were structurally characterized by X-ray diffraction (XRD) and Raman spectroscopy. The obtained XRD patterns were submitted to a Rietveld refinement showing, in both materials, a tetragonal phase with space group and point group of I41/a and C4h6, respectively. Microscopy images of both materials, obtained by field emission scanning electron microscopy, showed spherical agglomerated structures composed by spherical nanoparticles, while calcium and tungstate elements were identified by energy-dispersive X-ray spectroscopy for pure calcium tungstate and copper, calcium, and tungstate for Ca0.99Cu0.01WO4 solid solution. The decrease of optical band gap (Egap) from 4.0 eV (CaWO4) to 3.45 eV (Ca0.99Cu0.01WO4) confirmed the substitution of calcium atoms for copper atoms in the clusters [CaO8]. Maximum photoluminescence (PL) emission was shifted from 522 nm in the pure CaWO4 to 475 nm in the Ca0.99Cu0.01WO4 solid solution. Consequently, there was an increase of PL emissions intensity in the blue and green regions of the visible spectrum, due to electronic transitions between the orbitals O 2p, Cu 3d, and W 5d.

Solvent Effect on the Structural, Optical, Morphology, and Antimicrobial Activity of Silver Phosphate Microcrystals by Conventional Hydrothermal Method.

The design of particle size and morphology are a promising approach to investigating the properties exhibited by different types of materials. In the present study, the silver phosphate microcrystals (Ag3PO4) were first time synthesized using the hydrothermal and solvothermal method by combination of the solvents water/isopropyl alcohol (SP-IA), water/acetone (SP-AC), water/ammonium hydroxide (AP-AH), all in a ratio of 1:1 (v/v). The synthesized materials were structurally characterized by X-ray diffraction (XRD), Rietveld refinement, and Raman vibrational spectroscopy, where it was confirmed that the pure phase was achieved for all prepared samples. The study of the optical properties by UV-vis diffuse reflectance spectroscopy (UV-vis/DRS) and colorimetry revealed that the obtained materials have an optical bandgap between 2.30 and 2.32 eV. The FE-SEM images collected revealed different morphologies for the synthesized materials, with a predominance of tetraploid-shaped microcrystals for the SP-AC sample, rods for the SP-IA sample, cubes and polyhedral for the SP-WT sample and condensed polyhedral for the SP-AH sample. The photocatalytic performance against the Rhodamine B dye (RhB) was 100%, 98.2%, 94.2%, and 87.8%, using the samples SP-AC, SP-IA, SP-WT, and SP-AH as photocatalyst at time of 12 min. On the other hand, the antimicrobial performance of SP-AC sample showed superior performance, resulting in the minimum inhibitory concentration-MIC of 7.81 µg mL-1 for the strain of E. coli, 7.81 µg mL-1 for the strain of E. aureus, 15.62 µg mL-1 for the strain of P. auruginosa, and 15.62 µg mL-1 for the strains of C. albicans. In this way, was synthesized a promissory antimicrobial and photocatalyst material, through an easy and cost-effective method.