scholarly journals Characterization and Structural Insights of the Reaction Products by Direct Leaching of the Noble Metals Au, Pd and Cu with N,N′-Dimethyl-piperazine-2,3-dithione/I2 Mixtures

Molecules ◽  
2021 ◽  
Vol 26 (16) ◽  
pp. 4721
Author(s):  
Angela Serpe ◽  
Luca Pilia ◽  
Davide Balestri ◽  
Luciano Marchiò ◽  
Paola Deplano
Keyword(s):  
Density Functional ◽  
Noble Metals ◽  
Density Functional Theory Calculations ◽  
Metal Powders ◽  
Reaction Products ◽  
Metal Recycling ◽  
Direct Leaching ◽  
Tetrahedral Complexes ◽  
Organic Solutions ◽  
Structural Insights

In the context of new efficient and safe leaching agents for noble metals, this paper describes the capability of the Me2pipdt/I2 mixture (where Me2pipdt = N,N′-dimethyl-piperazine-2,3-dithione) in organic solutions to quantitatively dissolve Au, Pd, and Cu metal powders in mild conditions (room temperature and pressure) and short times (within 1 h in the reported conditions). A focus on the structural insights of the obtained coordination compounds is shown, namely [AuI2(Me2pipdt)]I3 (1), [Pd(Me2pipdt)2]I2 (2a) and [Cu(Me2pipdt)2]I3 (3), where the metals are found, respectively, in 3+, 2+ and 1+ oxidation states, and of [Cu(Me2pipdt)2]BF4 (4) and [Cu(Me2dazdt)2]I3 (5) (Me2dazdt = N,N′-dimethyl-perhydrodizepine-2,3-dithione) compared with 3. Au(III) and Pd(II) (d8 configuration) form square–planar complexes, whereas Cu(I) (d10) forms tetrahedral complexes. Density functional theory calculations performed on the cationic species of 1–5 help to highlight the nature of the bonding in the different complexes. Finally, the valorization of the noble metals-rich leachates is assessed. Specifically, gold metal is quantitatively recovered from the solution besides the ligands, showing the potential of these systems to promote metal recycling processes.

scholarly journals Reactivity of β-Substituted Phosphoenol Pyruvates towards Alkoxides: A Theoretical and Experimental Study

2018 ◽  
Vol 43 (3-4) ◽  
pp. 211-218
Author(s):  
Djilali Bassou ◽  
Amina Ghomri ◽  
Abdelkrim Atmani
Keyword(s):  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Atomic Charges ◽  
Reaction Products ◽  
Functional Theory ◽  
Reactivity Indices ◽  
Population Analyses ◽  
Major Reaction ◽  
Practical Synthesis ◽  
Global And Local

A new, practical, synthesis of pyruvic orthoesters relying on the conversion of β-substituted phosphoenol pyruvates by the action of alkoxides is described. Our study of the reaction mechanism was done experimentally and also theoretically. Density functional theory calculations were used to explain the major reaction products found experimentally. Geometry optimisations and atomic charges obtained using different population analyses and the global and local reactivity indices, namely global electrophilicity and the Parr function, were obtained at the B3LYP/6-311G(d) level of theory. The experimental reactivity was correctly reproduced using the Parr function.

Tailoring the Surface Reactivity: Comparison of Pd/Nb(110) and Rh/Nb(110)

2008 ◽  
Vol 73 (6-7) ◽  
pp. 745-754
Author(s):  
Štěpán Pick
Keyword(s):  
Density Functional Theory ◽  
First Principles ◽  
Density Functional ◽  
Noble Metals ◽  
Density Functional Theory Calculations ◽  
Surface Reactivity ◽  
Metallic Surfaces ◽  
Functional Theory ◽  
Metal Overlayers ◽  
Electron Occupation

Ni, Pd and Pt overlayers deposited on many metallic surfaces show properties resembling those of noble metals. We pose the question whether a similar trend might occur also for other transition-metal overlayers. To this goal, we perform first-principles density-functional theory calculations for Pd(111), Rh(111) surfaces, Pd and Rh epitaxial monolayers deposited on Nb(110), and for CO chemisorption on these systems. Density functional calculations indicate that the behavior of the two overlayers is quite different. Whereas the Rh overlayer on Nb(110) resembles the Rh(111) surface, for the Pd overlayer the electronic structure around the Fermi level is strongly affected by hybridization with Nb electrons, which accounts for unique properties of the overlayer. We expect that the latter mechanism may be of importance just for Pd, Pt, Ni and not for other transition metals with lower d-electron occupation.

Field Effect Modulation of Electrocatalytic Hydrogen Evolution at Back-Gated Two-Dimensional MoS2 Electrodes

2019 ◽  
Author(s):  
Yan Wang ◽  
Sagar Udyavara ◽  
Matthew Neurock ◽  
C. Daniel Frisbie
Keyword(s):  
Electric Field ◽  
Hydrogen Evolution ◽  
Active Sites ◽  
Density Functional ◽  
Electrode Materials ◽  
Density Functional Theory Calculations ◽  
Electronic Charge ◽  
Back Side ◽  
Gate Electrode ◽  
Conventional Manner

<div> <div> <div> <p> </p><div> <div> <div> <p>Electrocatalytic activity for hydrogen evolution at monolayer MoS2 electrodes can be enhanced by the application of an electric field normal to the electrode plane. The electric field is produced by a gate electrode lying underneath the MoS2 and separated from it by a dielectric. Application of a voltage to the back-side gate electrode while sweeping the MoS2 electrochemical potential in a conventional manner in 0.5 M H2SO4 results in up to a 140-mV reduction in overpotential for hydrogen evolution at current densities of 50 mA/cm2. Tafel analysis indicates that the exchange current density is correspondingly improved by a factor of 4 to 0.1 mA/cm2 as gate voltage is increased. Density functional theory calculations support a mechanism in which the higher hydrogen evolution activity is caused by gate-induced electronic charge on Mo metal centers adjacent the S vacancies (the active sites), leading to enhanced Mo-H bond strengths. Overall, our findings indicate that the back-gated working electrode architecture is a convenient and versatile platform for investigating the connection between tunable electronic charge at active sites and overpotential for electrocatalytic processes on ultrathin electrode materials.</p></div></div></div><br><p></p></div></div></div>

A New Phase of the Na+ Ion Conductor Na3PS4

2019 ◽  
Author(s):  
Theodosios Famprikis ◽  
James Dawson ◽  
François Fauth ◽  
Emmanuelle Suard ◽  
Benoit Fleutot ◽  
...  
Keyword(s):  
Solid Electrolytes ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Orthorhombic Crystal ◽  
Orthorhombic Crystal Structure ◽  
Ion Conductor ◽  
Solid State Batteries ◽  
Density Analysis ◽  
Two Phases ◽  
Dynamics Simulations

<div> <p>Solid electrolytes are crucial for next‑generation solid‑state batteries and Na<sub>3</sub>PS<sub>4</sub> is one of the most promising Na<sup>+</sup> conductors for such applications. At present, two phases of Na<sub>3</sub>PS<sub>4</sub> have been identified and it had been thought to melt above 500 °C. In contrast, we show that it remains solid above this temperature and transforms into a third polymorph, γ, exhibiting superionic behavior. We propose an orthorhombic crystal structure for γ‑Na<sub>3</sub>PS<sub>4</sub> based on scattering density analysis of diffraction data and density functional theory calculations. We show that the Na<sup>+</sup> superionic behavior is associated with rotational motion of the thiophosphate polyanions pointing to a rotor phase, based on <i>ab initio</i> molecular dynamics simulations and supported by high‑temperature synchrotron and neutron diffraction, thermal analysis and impedance spectroscopy. These findings are of importance for the development of new polyanion‑based solid electrolytes.</p> </div>

On the Linear Geometry of Lanthanide Hydroxide (Ln—OH, Ln=La-Lu)

2019 ◽  
Author(s):  
Hassan Harb ◽  
Lee Thompson ◽  
Hrant Hratchian
Keyword(s):  
Triple Bond ◽  
Density Functional ◽  
Valence Electron ◽  
Density Functional Theory Calculations ◽  
Electron Configuration ◽  
Functional Theory ◽  
Key Species ◽  
Pi Orbitals ◽  
Lanthanide Hydroxide ◽  
Linear Geometry

Lanthanide hydroxides are key species in a variety of catalytic processes and in the preparation of corresponding oxides. This work explores the fundamental structure and bonding of the simplest lanthanide hydroxide, LnOH (Ln=La-Lu), using density functional theory calculations. Interestingly, the calculations predict that all structures of this series will be linear. Furthermore, these results indicate a valence electron configuration featuring an occupied sigma orbital and two occupied pi orbitals for all LnOH compounds, suggesting that the lanthanide-hydroxide bond is best characterized as a covalent triple bond.

On the Linear Geometry of Lanthanide Hydroxide (Ln—OH, Ln=La-Lu)

2019 ◽  
Author(s):  
Hassan Harb ◽  
Lee Thompson ◽  
Hrant Hratchian
Keyword(s):  
Triple Bond ◽  
Density Functional ◽  
Valence Electron ◽  
Density Functional Theory Calculations ◽  
Electron Configuration ◽  
Functional Theory ◽  
Key Species ◽  
Pi Orbitals ◽  
Lanthanide Hydroxide ◽  
Linear Geometry

Lanthanide hydroxides are key species in a variety of catalytic processes and in the preparation of corresponding oxides. This work explores the fundamental structure and bonding of the simplest lanthanide hydroxide, LnOH (Ln=La-Lu), using density functional theory calculations. Interestingly, the calculations predict that all structures of this series will be linear. Furthermore, these results indicate a valence electron configuration featuring an occupied sigma orbital and two occupied pi orbitals for all LnOH compounds, suggesting that the lanthanide-hydroxide bond is best characterized as a covalent triple bond.

A New Interpretation of the Structure and Solvent Dependence of the Far UV Circular Dichroism Spectrum of Short Oligopeptides

2019 ◽  
Author(s):  
Anshuman Kumar ◽  
Reinhard Schweitzer-Stenner ◽  
Bryan Wong
Keyword(s):  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Cd Spectra ◽  
Functional Theory ◽  
Polyproline Ii ◽  
Solvent Dependence ◽  
Explicit Consideration ◽  
New Interpretation ◽  
Implicit And Explicit ◽  
Explicit Water

In this work, we carry out new time-dependent density functional theory calculations on the cationic tripeptide GAG in implicit and explicit water to determine the transitions that give rise to the observed CD signals of polyproline II and β-strand conformations. Our results reveal a plethora of electronic transitions that are governed by configurational interactions between multiple molecular orbital transitions of comparable energy. We also show that reproducing the CD spectra of polyproline II and β-strand conformations requires the explicit consideration of water molecules. The structure dependence of delocalized occupied orbitals contributes to the experimentally-observed invalidation of Flory’s isolated pair hypothesis.

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