On-the-Fly Ring-Polymer Molecular Dynamics Calculations of the Dissociative Photodetachment Process of the Oxalate Anion

The dissociative photodetachment dynamics of the oxalate anion, C2O4H− + hν → CO2 + HOCO + e−, were theoretically studied using the on-the-fly path-integral and ring-polymer molecular dynamics methods, which can account for nuclear quantum effects at the density-functional theory level in order to compare with the recent experimental study using photoelectron–photofragment coincidence spectroscopy. To reduce computational time, the force acting on each bead of ring-polymer was approximately calculated from the first and second derivatives of the potential energy at the centroid position of the nuclei beads. We find that the calculated photoelectron spectrum qualitatively reproduces the experimental spectrum and that nuclear quantum effects are playing a role in determining spectral widths. The calculated coincidence spectrum is found to reasonably reproduce the experimental spectrum, indicating that a relatively large energy is partitioned into the relative kinetic energy between the CO2 and HOCO fragments. This is because photodetachment of the parent anion leads to Franck–Condon transition to the repulsive region of the neutral potential energy surface. We also find that the dissociation dynamics are slightly different between the two isomers of the C2O4H− anion with closed- and open-form structures.

Crystal-to-Crystal Transformation from K2[Co(C2O4)2(H2O)2]·4H2O to K2[Co(μ-C2O4)(C2O4)]

Crystal-to-crystal transformation is a path to obtain crystals with different crystal structures and physical properties. K2[Co(C2O4)2(H2O)2]·4H2O (1) is obtained from K2C2O4·2H2O, CoCl2·6H2O in H2O with a yield of 60%. It is crystallized in the triclinic with space group P1 and cell parameters: a = 7.684(1) Å, b = 9.011(1) Å, c = 10.874(1) Å, α = 72.151(2)°, β = 70.278(2)°, γ = 80.430(2)°, V = 670.0(1) Å3, Z = 2 at 100 K. 1 is composed of K+, mononuclear anion [Co(C2O4)2(H2O)22−] and H2O. Co2+ is coordinated by two bidentated oxalate anion and two H2O in an octahedron environment. There is a hydrogen bond between mononuclear anion [Co(C2O4)2(H2O)22−] and H2O. K2[Co(μ-C2O4)(C2O4)] (2) is obtained from 1 by dehydration. The cell parameters of 2 are a = 8.460(5) Å, b = 6.906 (4) Å, c = 14.657(8) Å, β = 93.11(1)°, V = 855.0(8) Å3 at 100 K, with space group in P2/c. It is composed of K+ and zigzag [Co(μ-C2O4)(C2O42−]n chain. Co2+ is coordinated by two bisbendentate oxalate and one bidentated oxalate anion in trigonal-prism. 1 is an antiferromagnetic molecular crystal. The antiferromagnetic ordering at 8.2 K is observed in 2.

New chromium(III)-based catalysts for ethylene oligomerization

The report focuses on the new precatalysts for ethylene oligomerization. The five chromium(III) complex compounds containing the following ligands: dipicolinate anion, oxalate anion, 5-aminopyridine-2-carboxylate anion, 2,2′-bipyridine and 4,4′-dimethoxy-2,2′-bipyridine have been examined towards catalytic activity for ethylene oligomerization. The chromium(III) complexes have been activated by modified methylaluminoxane. The obtained oligomers have been investigated by MALDI-TOF–MS, thermal analysis and infrared spectroscopy. The results revealed that the examined chromium(III) complexes are highly active catalysts for ethylene oligomerization. The values of catalytic activities of the examined complexes are in the range 1860 – 3798 g∙mmol-1∙h-1∙bar-1.

Evaluation of the Corrosion Inhibiting Capacity of Silica/Polypyrrole-Oxalate Nanocomposite in Epoxy Coatings

Silica/Polypyrrole nanocomposites (SiO2/PPy) incorporating oxalate as counter anion (SiO2/PPyOx) were chemically polymerized in the solution with the presence of pyrrole, silica, and sodium oxalate. Nanocomposites SiO2/PPyOx at different concentrations of oxalate anion were characterized with FTIR, XRD, EDX, TGA, and TEM. The corrosion protective properties for carbon steel of nanocomposites in epoxy coating were studied by electrochemical techniques including electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP). FTIR results of nanocomposites show a slightly red-shift in terms of wavelength compared with the case of PPy and SiO2 spectra. It may be due to a better conjugation and interactions between PPy and SiO2 in nanocomposite structure. TEM image indicated that nanocomposites have spherical morphologies with diameters between 100 and 150 nm. The EIS results showed that |Z| modulus values of epoxy coatings containing SiO2/PPyOx composites reached about 109.7 Ω.cm2, always higher than that of epoxy coating. These results are also confirmed by OCP results. It proves that the presence of oxalate anion can enhance the resistance against corrosion and it has been shown that the content of counter anion strongly affects the anticorrosion ability.

Tl2C2O4·H2C2O4: a new crystalline form of thallium(I) oxalate

The title compound was prepared by reaction, in aqueous solution, of Tl2CO3 and H2C2O4·2H2O in a molar ratio of 1:2. Its crystal structure was solved by X-ray diffraction methods. It crystallizes in the monoclinic space group P21/a with Z = 2 molecules per unit cell. The oxalic acid molecule and the oxalate anion are planar, residing on crystallographic inversion centers, and linked to each other by strong O–H···O hydrogen bonds giving rise to a polymeric structure. The Tl(I) ion is in a distorted polyhedral coordination with nine neighboring O atoms, five of oxalate anions and four others of oxalic acid molecules. The FTIR and FT-Raman spectra of the compound were also recorded and are briefly discussed.

Carbonate coprecipitation preparation of Li-rich layered oxides using the oxalate anion ligand as high-energy, high-power and durable cathode materials for lithium-ion batteries

A green, highly efficient and low cost ligand oxalate anion is successfully introduced to prepare spherical precursors for high-energy, high-power and durable cathode materials.