Elucidating Structural Stability, Bandgap, and Photocatalytic Hydrogen Evolution of (H2 O/DMF)@HKUST-1 Host-guest Systems.

The H2 O@HKUST-1 and DMF@HKUST-1 systems were experimental and computationally assessed, employing XRD/TGA/FT-IR/DFT-calculations, evidencing that H2 O or DMF coordinated to Cu, modulating HKUST-1 photocatalytic properties. DMF@HKUST-1 has narrower bandgap promoting higher-crystallinity and light-harvesting. H2 O@HKUST-1 showed smaller particle sizing and sharp morphology. Theoretical models, (H2 O)1 @HKUST-1 and (DMF)1 @HKUST-1, containing one coordinated molecule, elucidated bandgap modulation associated with infiltration. H2 O@HKUST-1/DMF@HKUST-1 presented bandgaps [eV] of 3.6/3.4, by Tauc plots, and 3.55/3.26, by theoretical calculations, narrowing bandgap, compared with non-solvated HKUST-1(HKUST-1NS ). Both composites raised the valence band (VB) and lowered the conduction band (CB), but DMF@HKUST-1 most raised VB. Topological analysis revealed that guests i) with higher electronic density, raised VB, and ii) induced π-backbonding, lowering CB. DMF@HKUST-1 presented a higher photocatalytic hydrogen evolution (µmol), 26.45, in the first 30 min of the reaction, nevertheless, H2 O@HKUST-1 presented a competitive activity, of 17.32. In large periods, H2 O@HKUST-1/DMF@HKUST-1 showed practically the same hydrogen evolution, 45.50/49.03.

Experimental and Theoretical Studies on Acid Corrosion Inhibition of API 5L X70 Steel with Novel 1-N-α-d-Glucopyranosyl-1H-1,2,3-Triazole Xanthines.

A series of novel 1-N-α-d-glucopyranosyl-1H-1,2,3-triazole xanthines was synthesized from azido sugars (glucose, galactose, and lactose) and propargyl xanthines (theophylline and theobromine) using a typical copper (I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition. The corrosion inhibition activities of these new carbohydrate-xanthine compounds were evaluated by studying the corrosion of API 5 L X70 steel in a 1 M HCl medium. The results showed that, at 10 ppm, a 90% inhibition efficiency was reached by electrochemical impedance spectroscopy. The inhibitory efficiency of these molecules is explained by means of quantum chemical calculations of the protonated species with the solvent effect, which seems to better represent the actual situation of the experimental conditions. Some quantum chemical parameters were analyzed to characterize the inhibition performance of the tested molecules.

Adsorption and corrosion inhibition behaviour of new theophylline-triazole-based derivatives for steel in acidic medium.

The design and synthesis of a series of theophylline derivatives containing 1,2,3-triazole moieties are presented. The corrosion inhibition activities of these new triazole-theophylline compounds were evaluated by studying the corrosion of API 5 L X52 steel in 1 M HCl medium. The results showed that an increase in the concentration of the theophylline-triazole derivatives also increases the charge transference resistance (R ct) value, enhancing inhibition efficiency and decreasing the corrosion process. The electrochemical impedance spectroscopy under static conditions studies revealed that the best inhibition efficiencies (approx. 90%) at 50 ppm are presented by the all-substituted compounds. According to the Langmuir isotherm, the compounds 4 and 5 analysed exhibit physisorption-chemisorption process, with exception of the hydrogen 3, bromo 6 and iodo 7 substituted compounds, which exhibit chemisorption process. The corrosion when submerging a steel bar in 1 M HCl was studied using SEM-EDS. This experiment showed that the corrosion process decreases considerably in the presence of 50 ppm of the organic inhibitors. Finally, the theoretical study showed a correlation between EHOMO, hardness (η), electrophilicity (W), atomic charge and the inhibition efficiency in which the iodo 7 substituted compound presents the best inhibitor behaviour.

Composites of Anthraquinone Dyes@HKUST-1 with Tunable Microstructuring: Experimental and Theoretical Interaction Studies.

The metal-organic framework (MOF) HKUST-1 was employed as an interaction matrix for fundamental loading studies of anthraquinone dyes. Chosen dyes were alizarin (A), alizarin S (AS), disperse blue 1 (B1), disperse blue 3 (B3), disperse blue 56 (B56) and purpurin (P). All materials were characterized by XRD, FTIR, TGA and SEM. Hence the interaction of dyes with the framework was characterized by theoretical-experimental differential analysis. One-pot loading strategy resulted in more efficient scavenging of dyes, and reached 100 % for B56 using 50 mg L-1 . SEM revealed important microstructural changes, the smaller crystals ranged 0.8-3 µm in size and almost all composite sizes were from this to higher values, reaching 70 µm, with varying shapes. Two composites were larger in size range (about 2500-1000 µm), and were shaped as rods, octahedrons and coffin lids. Indeed, the microstructure could be modulated depending on preparation conditions and type of loaded dye. For the higher loading series, N2 adsorption and XPS experiments were carried on to further evidence dye-MOF interactions. Ab initio prediction of structural properties for A@HKUST-1 and P@HKUST-1 were obtained by means of solid-state CRYSTAL14 code at the PBE0 level of theory. Computed findings evidenced two O→Cu coordinative bonds, one from O-ketone and the other from O-phenolate moiety as main interactions towards CuNET centers.

Roothaan's approach to solve the Hartree-Fock equations for atoms confined by soft walls: Basis set with correct asymptotic behavior.

In this report, we use a new basis set for Hartree-Fock calculations related to many-electron atoms confined by soft walls. One- and two-electron integrals were programmed in a code based in parallel programming techniques. The results obtained with this proposal for hydrogen and helium atoms were contrasted with other proposals to study just one and two electron confined atoms, where we have reproduced or improved the results previously reported. Usually, an atom enclosed by hard walls has been used as a model to study confinement effects on orbital energies, the main conclusion reached by this model is that orbital energies always go up when the confinement radius is reduced. However, such an observation is not necessarily valid for atoms confined by penetrable walls. The main reason behind this result is that for atoms with large polarizability, like beryllium or potassium, external orbitals are delocalized when the confinement is imposed and consequently, the internal orbitals behave as if they were in an ionized atom. Naturally, the shell structure of these atoms is modified drastically when they are confined. The delocalization was an argument proposed for atoms confined by hard walls, but it was never verified. In this work, the confinement imposed by soft walls allows to analyze the delocalization concept in many-electron atoms.

Katoite under pressure: an ab initio investigation of its structural, elastic and vibrational properties sheds light on the phase transition.

The evolution under pressures up to 65 GPa of structural, elastic and vibrational properties of the katoite hydrogarnet, Ca3Al2(OH)12, is investigated with an ab initio simulation performed at the B3LYP level of theory, by using all-electron basis sets with the Crystal periodic program. The high-symmetry Ia3d phase of katoite, stable under ambient conditions, is shown to be destabilized, as pressure increases, by interactions involving hydrogen atoms and their neighbors which weaken the hydrogen bonding network of the structure. The corresponding thermodynamical instability is revealed by anomalous deviations from regularity of its elastic constants and by numerous imaginary phonon frequencies, up to 50 GPa. Interestingly, as pressure is further increased above 50 GPa, the Ia3d structure is shown to become stable again (all positive phonon frequencies and regular elastic constants). However, present calculations suggest that, above about 15 GPa and up to at least 65 GPa, a phase of I4[combining macron]3d symmetry (a non-centrosymmetric subgroup of Ia3d) becomes more stable than the Ia3d one, being characterized by strengthened hydrogen bonds. At low-pressures (between about 5 GPa and 15 GPa), both phases show some instabilities (more so for I4[combining macron]3d than for Ia3d), thus suggesting either the existence of a third phase or a possible phase transition of second order.

Electronic charge density analysis of Li-doped polyacetylene: molecular vs periodic descriptions and nature of Li-to-chain bonding.

A detailed analysis of the electronic structure and charge distribution around the trigonal site of Li-doped polyacetylene is reported using finite chain and periodic descriptions of the polymer. Atoms-in-molecules (AIM) analysis is done to characterize the nature of the bond between Li and the polymer backbone through the location of the bond critical points and computation of the total charge on the atomic basins around the doping site. We find that the Li atom donates practically one electron to the π-system, in accordance with the classical Su-Schriffer-Heeger model. However, despite that the Li atom is equidistant from the three closest C atoms in the geometric soliton, a single Li-C bond critical point is found. The AIM quantitative analysis of the electronic density reveals that the Li(+) ion is immersed into the polymer π-cloud in a way that resembles a metallic bonding interaction.

Hydrolysis of TiCl(4): initial steps in the production of TiO(2).

The hydrolysis of titanium tetrachloride (TiCl(4)) to produce titanium dioxide (TiO(2)) nanoparticles has been studied to provide insight into the mechanism for forming these nanoparticles. We provide calculations of the potential energy surfaces, the thermochemistry of the intermediates, and the reaction paths for the initial steps in the hydrolysis of TiCl(4). We assess the role of the titanium oxychlorides (Ti(x)O(y)Cl(z); x = 2-4, y = 1, 3-6, and z = 2, 4, 6) and their viable reaction paths. Using transition-state theory and RRKM theory, we predicted rate constants including the effect of tunneling. Heats of formation at 0 and 298 K are predicted for TiCl(4), TiCl(3)OH, TiOCl(2), TiOClOH, TiCl(2)(OH)(2), TiCl(OH)(3), Ti(OH)(4), and TiO(2) using the CCSD(T) method with correlation consistent basis sets extrapolated to the complete basis set limit and compared with the available experimental data. Clustering energies and heats of formation are calculated for neutral clusters. The calculated heats of formation were used to study condensation reactions that eliminate HCl or H(2)O. The reaction energy is substantially endothermic if more than two HCl molecules are eliminated. The results show that the mechanisms leading to formation of TiO(2) nanoparticles and larger ones are complicated and will have a strong dependence on the experimental conditions.

The Kohn-Sham kinetic energy density as indicator of the electron localization: atomic shell structure.

In this report, it is shown that the Kohn-Sham (KS) kinetic energy density (KED) contains the average local electrostatic potential (ALEP) and the average local ionization energy (ALIE); the shell structure in atomic systems is presented as one application of the KS-KED. By writing the KS-KED from the KS equations, this quantity was divided in three contributions: orbital, Coulomb, and exchange correlation. By studying several closed and open shell atoms, the shell structure was established by the maxima presented by the Coulomb contribution and the minima in the orbital contribution of the KS-KED. The exchange-correlation contribution to the KS-KED does not show maxima or minima, but this quantity shows bumps where the division between shells is expected. The results obtained in this work were compared with other shell structure indicators such as the electron localization function, the ALEP, the ALIE, and the radial distribution function. The most important result in this work is related to the fact that even when the ALEP and the ALIE functions were built with different arguments to each other, they are contained in the KS-KED. In this way, the KS-KED shows its importance to reveal the electron localization in atomic systems.

Relationship between the critical points found by the electron localization function and atoms in molecules approaches in adducts with hydrogen bonds.

In this work, 11 adducts with hydrogen bonds were studied by using the B3LYP exchange-correlation functional of the Kohn-Sham approach and the Møller-Plesset second-order perturbation theory MP2. With both approaches, the geometry of each adduct was optimized with the aug-cc-pVTZ basis set. The binding energies of the considered systems, found by the MP2 method, range from 1.2 to 8.3 kcal/mol. By using the atoms in molecules (AIM) analysis and the electron localization function (ELF) we found that the critical points positions characteristic of hydrogen bonds obtained by AIM and ELF are very similar each other. Besides, we found a linear correlation between the critical points positions found by AIM and those obtained by ELF with the B3LYP method and also with the MP2 method. The slope of such a linear relationship was close to 1 and the y-intercept close to 0.