DFT mechanistic studies on the epoxidation of cyclohexene by non-heme tetraaza manganese complexes

2009 ◽  
Vol 87 (1) ◽  
pp. 33-38 ◽  
Author(s):  
Alicja Haras ◽  
Tom Ziegler
Keyword(s):  
Density Functional ◽  
Direct Transfer ◽  
Energy Landscapes ◽  
Olefin Epoxidation ◽  
Mechanistic Studies ◽  
Metal Centre ◽  
Functional Theory ◽  
Homolytic Decomposition ◽  
Experimental Findings ◽  
Epoxidation Of Cyclohexene

Herein, we report density functional calculations on the epoxidation of cyclohexene with H2O2 activated by (Me2EBC)MnCl2 (Me2EBC stands for 4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane). The computed energy landscapes for different interaction modes of cyclohexene with the MnIV-hydroperoxo complex and the MnV-oxo species support recent experimental findings by Busch and co-workers [J. Am. Chem. Soc. 127, 17170 (2005)], according to which the MnIV-hydroperoxo species is the active complex for olefin epoxidation. Thus, the dominant olefin epoxidation pathway is via direct transfer of the distal protonated oxygen of the hydroperoxo adduct without changes in the oxydation state of its tetravalent metal centre, i.e., the mechanism commonly observed in the uncatalyzed epoxidation by peracids. The homolytic decomposition of the O–OH bond in the active manganese complex leading to the MnV-oxo species is found to be the only epoxidation pathway that could possibly compete with the Oβ transfer from the hydroperoxo adduct. However, the generated MnV-oxo is shown to be a rather poor oxidant resulting in low yields of the target epoxy cyclohexane.Key words: epoxidation, density functional theory, permanganic acid, peracid.

scholarly journals Quasi-1D XY antiferromagnet Sr2Ni(SeO3)2Cl2 at Sakai-Takahashi phase diagram

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
E. S. Kozlyakova ◽  
A. V. Moskin ◽  
P. S. Berdonosov ◽  
V. V. Gapontsev ◽  
S. V. Streltsov ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Long Range ◽  
Density Functional ◽  
Uniaxial Anisotropy ◽  
Exchange Interactions ◽  
Spin Liquid ◽  
Functional Theory ◽  
One Dimensional ◽  
Ordered Phases ◽  
Experimental Findings

AbstractUniform quasi-one-dimensional integer spin compounds are of interest as a potential realization of the Haldane conjecture of a gapped spin liquid. This phase, however, has to compete with magnetic anisotropy and long-range ordered phases, the implementation of which depends on the ratio of interchain J′ and intrachain J exchange interactions and both uniaxial D and rhombic E single-ion anisotropies. Strontium nickel selenite chloride, Sr2Ni(SeO3)2Cl2, is a spin-1 chain system which passes through a correlations regime at Tmax ~ 12 K to long-range order at TN = 6 K. Under external magnetic field it experiences the sequence of spin-flop at Bc1 = 9.0 T and spin-flip transitions Bc2 = 23.7 T prior to full saturation at Bsat = 31.0 T. Density functional theory provides values of the main exchange interactions and uniaxial anisotropy which corroborate the experimental findings. The values of J′/J = 0.083 and D/J = 0.357 place this compound into a hitherto unoccupied sector of the Sakai-Takahashi phase diagram.

scholarly journals High-pressure studies of palladium and platinum thioether macrocyclic dihalide complexes

2014 ◽  
Vol 70 (3) ◽  
pp. 469-486 ◽  
Author(s):  
David R. Allan ◽  
Daniel Bailey ◽  
Nigel Bird ◽  
Alexander J. Blake ◽  
Neil R. Champness ◽  
...  
Keyword(s):  
High Pressure ◽  
Density Functional ◽  
Metal Centre ◽  
Functional Theory ◽  
Chain Polymer ◽  
Metal Interactions ◽  
Metal Interaction ◽  
High Pressure Studies ◽  
Distorted Octahedral ◽  
Halide Ligands

The mononuclear macrocyclic PdIIcomplexcis-[PdCl2([9]aneS3)] ([9]aneS3= 1,4,7-trithiacyclo-nonane) converts at 44 kbar into an intensely coloured chain polymer exhibiting distorted octahedral coordination at the metal centre and an unprecedented [1233] conformation for the thioether ligand. The evolution of an intramolecular axial sulfur–metal interaction and an intermolecular equatorial sulfur–metal interaction is central to these changes. High-pressure crystallographic experiments have also been undertaken on the related complexes [PtCl2([9]aneS3)], [PdBr2([9]aneS3)], [PtBr2([9]aneS3)], [PdI2([9]aneS3)] and [PtI2([9]aneS3)] in order to establish the effects of changing the halide ligands and the metal centre on the behaviour of these complexes under pressure. While all complexes undergo contraction of the various interaction distances with increasing pressure, only [PdCl2([9]aneS3)] undergoes a phase change. Pressure-induced I...I interactions were observed for [PdI2([9]aneS3)] and [PtI2([9]aneS3)] at 19 kbar, but the corresponding Br...Br interactions in [PdBr2([9]aneS3)] and [PtBr2([9]aneS3)] only become significant at much higher pressure (58 kbar). Accompanying density functional theory (DFT) calculations have yielded interaction energies and bond orders for the sulfur–metal interactions.

Visible-light Photoresponse of Nitrogen-doped TiO2: Excited State Studies Using Time-dependent Density Functional Theory and Equation-of-Motion Coupled Cluster Methods

2010 ◽  
Vol 1263 ◽  
Author(s):  
Niranjan Govind ◽  
Roger Rousseau ◽  
Amity Andersen ◽  
Karol Kowalski
Keyword(s):  
Excited State ◽  
Density Functional ◽  
Equation Of Motion ◽  
Coupled Cluster ◽  
Functional Theory ◽  
Experimental Findings ◽  
High Level ◽  
Cluster Methods ◽  
Compare And Contrast

AbstractTo shed light on the nature of the electronic states at play in N-doped TiO2 nanoparticles, we have performed detailed ground and excited state calculations on pure and N-doped TiO2 rutile using an embedding model. We have validated our model by comparing ground-state embedded results with those obtained from periodic DFT calculations. Our results are consistent with periodic calculations. Using this embedding model we have performed B3LYP based TDDFT calculations of the excited state spectrum. We have also studied the lowest excitations using high-level equation-of-motion coupled cluster (EOMCC) approaches involving all single and inter-band double excitations. We compare and contrast the nature of the excitations in detail for the pure and doped systems using these calculations. Our calculations indicate a lowering of the bandgap and confirm the role of the N3- states on the UV/Vis spectrum of N-doped TiO2 rutile supported by experimental findings.

scholarly journals First principles calculations on theoretical band gap improvement of IIIA-VA zinc-blende semiconductor InAs

2020 ◽  
Vol 31 (12) ◽  
pp. 2050178
Author(s):  
Waqas Mahmood ◽  
Arfan Bukhtiar ◽  
Muhammad Haroon ◽  
Bing Dong
Keyword(s):  
Band Gap ◽  
Density Functional ◽  
Local Density ◽  
Lattice Parameter ◽  
First Principles Calculations ◽  
Functional Theory ◽  
Zinc Blende ◽  
Valence States ◽  
Direct Band ◽  
Experimental Findings

The structural, electronic, dielectric and vibrational properties of zinc-blende (ZB) InAs were studied within the framework of density functional theory (DFT) by employing local density approximation and norm-conserving pseudopotentials. The optimal lattice parameter, direct band gap, static dielectric constant, phonon frequencies and Born effective charges calculated by treating In-4d electrons as valence states are in satisfactory agreement with other reported theoretical and experimental findings. The calculated band gap is reasonably accurate and improved in comparison to other findings. This work will be useful for more computational studies related to semiconductor devices.

scholarly journals Ultrafast optically induced spin transfer in ferromagnetic alloys

2020 ◽  
Vol 6 (3) ◽  
pp. eaay8717 ◽  
Author(s):  
M. Hofherr ◽  
S. Häuser ◽  
J. K. Dewhurst ◽  
P. Tengdin ◽  
S. Sakshath ◽  
...  
Keyword(s):  
Density Functional ◽  
Spin Dynamics ◽  
Research Area ◽  
Spin Transfer ◽  
Optical Manipulation ◽  
Functional Theory ◽  
Control Schemes ◽  
All Optical ◽  
Spin Excitations ◽  
Experimental Findings

The vision of using light to manipulate electronic and spin excitations in materials on their fundamental time and length scales requires new approaches in experiment and theory to observe and understand these excitations. The ultimate speed limit for all-optical manipulation requires control schemes for which the electronic or magnetic subsystems of the materials are coherently manipulated on the time scale of the laser excitation pulse. In our work, we provide experimental evidence of such a direct, ultrafast, and coherent spin transfer between two magnetic subsystems of an alloy of Fe and Ni. Our experimental findings are fully supported by time-dependent density functional theory simulations and, hence, suggest the possibility of coherently controlling spin dynamics on subfemtosecond time scales, i.e., the birth of the research area of attomagnetism.

Accurate predictions of C–SO2R bond dissociation enthalpies using density functional theory methods

2014 ◽  
Vol 16 (38) ◽  
pp. 20964-20970 ◽  
Author(s):  
Hai-Zhu Yu ◽  
Fang Fu ◽  
Liang Zhang ◽  
Yao Fu ◽  
Zhi-Min Dang ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Mechanistic Studies ◽  
Functional Theory ◽  
Bond Dissociation

M06-2X/6-31G(d) was found to be accurate in calculating C–S BDEs, and preliminary mechanistic studies were performed using it.

scholarly journals Symmetry/Asymmetry of the NHN Hydrogen Bond in Protonated 1,8-Bis(dimethylamino)naphthalene

Symmetry ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 1924
Author(s):  
Patrycja Piękoś ◽  
Aneta Jezierska ◽  
Jarosław J. Panek ◽  
Eugene A. Goremychkin ◽  
Alexander F. Pozharskii ◽  
...  
Keyword(s):  
Density Functional ◽  
Inelastic Neutron Scattering ◽  
Inelastic Neutron ◽  
Functional Theory ◽  
Protonated Forms ◽  
Motional Dynamics ◽  
Proton Dynamics ◽  
Experimental Findings ◽  
Bridge Vibrations ◽  
Theoretical Results

Experimental and theoretical results are presented based on vibrational spectra and motional dynamics of 1,8-bis(dimethylamino)naphthalene (DMAN) and its protonated forms (DMANH+ and the DMANH+ HSO4− complex). The studies of these compounds have been performed in the gas phase and solid-state. Spectroscopic investigations were carried out by infrared spectroscopy (IR), Raman, and incoherent inelastic neutron scattering (IINS) experimental methods. Density functional theory (DFT) and Car–Parrinello molecular dynamics (CPMD) methods were applied to support our experimental findings. The fundamental investigations of hydrogen bridge vibrations were accomplished on the basis of isotopic substitutions (NH → ND). Special attention was paid to the bridged proton dynamics in the DMANH+ complex, which was found to be affected by interactions with the HSO4− anion.

scholarly journals Fluorescent Calix[4]arene-Carbazole-Containing Polymers as Sensors for Nitroaromatic Explosives

Chemosensors ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 128
Author(s):  
Patrícia D. Barata ◽  
José V. Prata
Keyword(s):  
Density Functional ◽  
Picric Acid ◽  
High Sensitivity ◽  
Functional Theory ◽  
Sensitivity And Selectivity ◽  
Polymer Models ◽  
Photo Induced Electron Transfer ◽  
Experimental Findings ◽  
Detection Of Explosives

Two highly fluorescent calix[4]arene-containing phenylene-alt-ethynylene-carbazolylene polymers (Calix-PPE-CBZs) were used in the detection of explosives from the nitroaromatic compounds (NACs) family, in solution and in vapour phases. Both fluorophores exhibit high sensitivity and selectivity towards NACs detection. The quenching efficiencies in solution, assessed through static Stern-Volmer constants (KSV), follow the order picric acid (PA) >> 2,4,6-trinitrotoluene (TNT) > 2,4-dinitrotoluene > (2,4-DNT) > nitrobenzene (NB). These correlate very well with the NACs electron affinities, as evaluated from their lowest unoccupied molecular orbitals (LUMOs) energies, indicating a photo-induced electron transfer as the dominant mechanism in fluorescence quenching. Moreover, and most interesting, detection of TNT, 2,4-DNT and NB vapours via thin-films of Calix-PPE-CBZs revealed a remarkably sensitive response to these analytes, comparable to state-of-the-art chemosensors. The study also analyses and compares the current results to previous disclosed data on the detection of NACs by several calix[4]arene-based conjugated polymers and non-polymeric calix[4]arenes-carbazole conjugates, overall highlighting the superior role of calixarene and carbazole structural motifs in NACs’ detection performance. Density functional theory (DFT) calculations performed on polymer models were used to support some of the experimental findings.

Systematic first principles calculations of the effects of stacking faults defects on the 4H-SiC band structure

2010 ◽  
Vol 1246 ◽  
Author(s):  
Massimo Camarda ◽  
pietro delugas ◽  
Andrea Canino ◽  
Andrea Severino ◽  
nicolo piluso ◽  
...  
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Stacking Faults ◽  
Perfect Crystal ◽  
First Principles Calculations ◽  
Electronic Band ◽  
Functional Theory ◽  
Experimental Findings ◽  
Electronic Band Structures ◽  
Formation Energies

AbstractShockley-type Stacking faults (SSF) in hexagonal Silicon Carbide polytypes have received considerable attention in recent years since it has been found that these defects are responsible for the degradation of forward I-V characteristics in p-i-n diodes. In order to extend the knowledge on these kind of defects and theoretically support experimental findings (specifically, photoluminescence spectral analysis), we have determined the Kohn-Sham electronic band structures, along the closed path Γ-M-K-Γ, using density functional theory. We have also determined the energies of the SSFs with respect to the perfect crystal finding that the (35) and (44) SSFs have unexpectedly low formation energies, for this reason we could expect these two defects to be easily generated/expanded either during the growth or post-growth process steps.

scholarly journals Quantum plasmonics: from jellium models to ab initio calculations

Nanophotonics ◽  
2016 ◽  
Vol 5 (3) ◽  
pp. 409-426 ◽  
Author(s):  
Alejandro Varas ◽  
Pablo García-González ◽  
Johannes Feist ◽  
F.J. García-Vidal ◽  
Angel Rubio
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Plasmonic Nanostructures ◽  
Functional Theory ◽  
Fundamental Understanding ◽  
Invaluable Tool ◽  
Classical Models ◽  
Light Matter Interaction ◽  
Experimental Findings ◽  
The Impact

AbstractLight-matter interaction in plasmonic nanostructures is often treated within the realm of classical optics. However, recent experimental findings show the need to go beyond the classical models to explain and predict the plasmonic response at the nanoscale. A prototypical system is a nanoparticle dimer, extensively studied using both classical and quantum prescriptions. However, only very recently, fully ab initio time-dependent density functional theory (TDDFT) calculations of the optical response of these dimers have been carried out. Here, we review the recent work on the impact of the atomic structure on the optical properties of such systems. We show that TDDFT can be an invaluable tool to simulate the time evolution of plasmonic modes, providing fundamental understanding into the underlying microscopical mechanisms.

Sign in / Sign up

Export Citation Format

Share Document